Antibacterial biological graphene food packaging wrapping film and preparation process thereof

Abstract

The invention discloses an antibacterial biological graphene food packaging wrapping film and a preparation process of the antibacterial biological graphene food packaging wrapping film, and belongs to the technical field of functional food packaging materials. Silver zinc oxide composite functionalized graphene oxide and quaternary ammonium salt chitosan grafted reduced graphene oxide are introduced to serve as key functional filler, and the composite film is prepared through blending dispersion and casting film forming processes. The preparation method is characterized in that two fillers are respectively prepared at first, wherein the former filler is obtained by co-reducing and depositing silver and zinc oxide nanoparticles on graphene oxide through sodium borohydride; the quaternary ammonium salt chitosan is grafted to graphene oxide through an amidation reaction, and then reduction is carried out through ascorbic acid to obtain the quaternary ammonium salt chitosan / graphene oxide composite material. Through the synergistic effect of the two fillers, the film is endowed with high-efficiency broad-spectrum antibacterial performance, and the mechanical strength and barrier property are remarkably improved. The technology is safe and environmentally friendly, the obtained wrapping film is biodegradable and suitable for fresh food fresh-keeping packaging, and the shelf life is effectively prolonged.

Description

Technical Field

[0001] This invention relates to the field of functional food packaging materials technology, specifically to an antibacterial bio-graphene food packaging stretch film and its preparation process. Background Technology

[0002] With increasing global emphasis on environmental protection and food safety, developing new biodegradable food packaging materials with active preservation functions has become an important research direction in the fields of packaging science and materials engineering. Traditional petroleum-based plastic packaging films are difficult to degrade, causing serious "white pollution," and their single function cannot effectively inhibit microbial spoilage and oxidative deterioration of food during storage and transportation, failing to meet the social demands for green and sustainable development. Therefore, bio-based biodegradable polymers, such as plant-derived starch, animal or fungal-derived chitosan, and polyhydroxyalkanoates synthesized by microbial fermentation, are highly favored due to their renewable sources and ultimate return to the natural cycle. However, these materials face significant bottlenecks in their practical application: their mechanical properties are generally inferior to traditional plastics, their ability to block oxygen and water vapor is generally insufficient, and, more importantly, most natural biopolymers themselves do not possess sufficient or long-lasting antibacterial activity. These shortcomings make it difficult for simple bio-based packaging films to replace traditional plastics in harsh preservation environments, hindering their industrialization and commercialization.

[0003] To overcome the aforementioned performance shortcomings, researchers have extensively explored the introduction of various nanofillers into biopolymer matrices to construct composite materials. Among numerous nanomaterials, graphene and its derivatives, especially graphene oxide, demonstrate great application potential due to their extremely high specific surface area, excellent intrinsic mechanical strength, and certain natural antibacterial potential. Existing technologies show that adding graphene oxide or reduced graphene oxide to matrices such as chitosan and polyvinyl alcohol can improve the mechanical and barrier properties of composite films to a certain extent. However, this simple physical blending faces fundamental challenges: the strong van der Waals forces between graphene sheets cause them to easily aggregate in the polymer matrix, making it difficult to achieve uniform dispersion at the nanoscale. This not only limits the full realization of its reinforcing effect but may also cause film defects. Furthermore, unmodified graphene mainly exerts its antibacterial effect by physically disrupting bacterial cell membranes, which has limited efficiency, a narrow antibacterial spectrum, and a passive mechanism of action, making it difficult to cope with complex food contamination environments. Therefore, effectively functionalizing graphene to improve its dispersibility, interfacial compatibility, and endow it with stronger and more active antibacterial functions has become the key to technological breakthroughs in this field.

[0004] To address the shortcomings of existing technologies, this invention aims to provide an innovative solution. The core of this invention lies in the design and preparation of two novel, functionally synergistic modified graphene materials, which are then simultaneously introduced into a biopolymer matrix. The first material, through a clever chemical process, simultaneously constructs a composite antibacterial system on graphene oxide sheets, where silver nanoparticles and zinc oxide nanoparticles coexist, achieving a synergistic effect of multiple antibacterial mechanisms, including metal ion release and photocatalytic reactive oxygen species generation. The second material, through covalent grafting technology, firmly anchors quaternary ammonium salt-modified chitosan molecular chains with long-lasting cationic antibacterial properties onto the reduced graphene oxide backbone. This significantly improves the compatibility and dispersibility of the nanofiller with the matrix while introducing positively charged antibacterial groups. Using these two modified materials together to reinforce a polyvinyl alcohol and starch composite system not only significantly enhances the mechanical strength and shielding performance against water vapor and oxygen through the physical barrier and reinforcing effects of graphene, but also constructs a three-dimensional antibacterial network combining "rapid contact sterilization" and "long-lasting sustained-release antibacterial action." This technical solution uses aqueous solvents and commercially available raw materials throughout the entire process, making it safe and environmentally friendly. The resulting stretch film has excellent comprehensive performance, significant antibacterial effect, and good biodegradability, providing a practical new path for developing next-generation high-performance active food packaging materials. Summary of the Invention

[0005] The purpose of this invention is to provide an antibacterial bio-graphene food packaging wrapping film and its preparation process, which solves the technical problems that existing biodegradable food packaging films cannot meet the requirements for fresh food preservation due to poor mechanical and barrier properties, single or inefficient antibacterial functions, and the difficulty in balancing high performance and green safety.

[0006] The present invention achieves the above objectives through the following technical solutions: A process for preparing an antibacterial bio-graphene food packaging stretch film, comprising the following steps: S1. By weight, add 60-80 parts of polyvinyl alcohol and 20-40 parts of starch to a three-necked flask containing a mixed solvent of 400-600 parts of deionized water and 15-25 parts of glycerol. Stir continuously in a water bath at 88-92℃ and cool to 58-62℃ to obtain a gel. Add a deionized water dispersion containing 0.5-3.0 parts of silver-zinc oxide composite functionalized graphene oxide to the gel and shear emulsify. Add 2.0-8.0 parts of quaternary ammonium salted chitosan-grafted reduced graphene oxide, continue shearing, and then transfer to an ice-water bath for ultrasonic treatment to obtain a composite casting solution. S2. Vacuum degas the composite casting liquid and then pour it onto a polytetrafluoroethylene (PTFE) casting plate. Use a scraper to control the thickness of the wet film. Place the PTFE casting plate in a forced-air drying oven and dry it at a constant temperature of 34-36℃. After the wet film is formed, peel it off from the substrate to obtain a thin film. Place the thin film at 24-26℃ to equilibrate.

[0007] In this invention, during the film-forming process of the antibacterial bio-graphene food packaging stretch film, the biopolymer adhesive, the deionized aqueous dispersion of silver-zinc oxide composite functionalized graphene oxide, and the reduced graphene oxide grafted with quaternized chitosan are uniformly dispersed at the nanoscale through the synergistic action of high-speed shearing and ice-bath ultrasonication. During the drying stage, moisture evaporates slowly, and hydrogen bonds and physical entanglements are formed between the polymer molecular chains and the nanofillers, constructing a dense three-dimensional network. Nano-silver and zinc oxide in the film exert broad-spectrum antibacterial effects through ion slow-release, while the quaternary ammonium salt groups destroy microbial cell membranes with positive charges, achieving contact sterilization. These three elements synergistically enhance antibacterial efficacy. The graphene sheets significantly improve mechanical strength and gas barrier properties, while the bio-matrix ensures environmental friendliness. The entire process is aqueous, leaving no toxic solvent residues, resulting in a safe, biodegradable stretch film suitable for food preservation.

[0008] According to a preferred embodiment of the present invention, in step S1, the stirring time in a water bath at 88-92°C is 3-4 hours.

[0009] According to a preferred embodiment of the present invention, in step S2, the drying time at a constant temperature of 34-36°C is 24-36 hours.

[0010] According to a preferred embodiment of the present invention, the method for preparing the deionized aqueous dispersion of the silver-zinc oxide composite functionalized graphene oxide includes: A1. The deionized aqueous dispersion of graphene oxide was ultrasonically treated in an ice-water bath; under stirring and nitrogen protection, silver nitrate and zinc nitrate hexahydrate were added to obtain a mixture; the mixture was heated to 58-62℃, and pre-cooled sodium borohydride aqueous solution was added dropwise under stirring, and the reaction was continued at 58-62℃ to obtain a reaction mixture. A2. Cool the reaction mixture to room temperature, centrifuge to obtain a solid precipitate, wash the solid precipitate alternately with deionized water and anhydrous ethanol to obtain a washed solid precipitate; redisperse the washed solid precipitate in deionized water.

[0011] In this invention, the preparation of the deionized aqueous dispersion of the silver-zinc oxide composite functionalized graphene oxide is based on the abundant oxygen-containing functional groups on the surface of the graphene oxide sheets. Under an inert atmosphere, the metal cations of soluble silver and zinc salts are selectively adsorbed onto the sheet surface through electrostatic interactions. Upon introduction of a reducing agent, the system becomes alkaline due to hydrolysis, where silver ions are reduced in situ to silver nanoparticles, and zinc ions are converted to zinc oxide nanoparticles via a zinc hydroxide intermediate under thermal action. Both are synergistically anchored to the graphene oxide sheets, forming a stable composite structure. The product is centrifuged, repeatedly washed with water and ethanol to remove impurities, and finally redispersed in deionized water to obtain a uniformly dispersed, non-agglomerated aqueous dispersion system of the functional filler, providing a highly active antibacterial unit for subsequent composite processing.

[0012] According to a preferred embodiment of the present invention, in step A1, the reaction is continued at 58-62°C for 4-6 hours.

[0013] According to a preferred embodiment of the present invention, in step A2, the centrifugation time is 20-40 min.

[0014] According to a preferred embodiment of the present invention, the method for preparing the quaternized chitosan-grafted reduced graphene oxide includes: B1. Chitosan was dissolved in an aqueous acetic acid solution, glycidyltrimethylammonium chloride was added, and the mixture was stirred in a water bath at 68-72℃ to obtain a reaction solution. The reaction solution was precipitated with acetone, filtered, washed with ethanol, and vacuum dried to obtain quaternized chitosan solid. A deionized aqueous dispersion of graphene oxide was added to 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide and activated at room temperature. Quaternized chitosan solid dissolved in acetic acid solution was added, and the pH was adjusted to 5.4-5.6 with sodium hydroxide solution. The mixture was stirred in a nitrogen atmosphere at 58-62℃ to obtain an intermediate mixture. B2. Add ascorbic acid to the intermediate mixture and continue the reaction at 78-82℃ to obtain a reaction mixture; centrifuge the reaction mixture to obtain a solid precipitate, wash the solid precipitate with dilute hydrochloric acid and deionized water, and freeze-dry it.

[0015] In this invention, the preparation of reduced graphene oxide grafted with quaternized chitosan involves two steps: First, chitosan is modified with a quaternizing agent to generate quaternized chitosan with enhanced water solubility and a positive charge. Separately, a separately prepared graphene oxide dispersion is activated with a carboxyl activator, and then undergoes a condensation reaction with the amino groups of the quaternized chitosan under weakly acidic conditions, achieving covalent grafting through amide bonds to form an intermediate. Subsequently, a reducing agent is added to reduce the graphene oxide to reduced graphene oxide under mild conditions, while effectively maintaining the integrity of the amide bond structure. The product is washed with a weakly acidic solution to remove physically adsorbed components, then washed with water until neutral, and freeze-dried to obtain a black powder. This material combines the mechanical reinforcing properties of graphene with the contact bactericidal ability of quaternary ammonium salts, and the grafted structure is stable.

[0016] According to a preferred embodiment of the present invention, in step B1, the stirring reaction is carried out for 12-14 hours at a nitrogen atmosphere and a temperature of 58-62°C.

[0017] According to a preferred embodiment of the present invention, in step B2, the reaction continues at 78-82°C for 6-8 hours.

[0018] The present invention also provides an antibacterial bio-graphene food packaging stretch film prepared according to the preparation process of the aforementioned antibacterial bio-graphene food packaging stretch film.

[0019] The beneficial effects of this invention are as follows: The antibacterial bio-graphene food packaging stretch film and its preparation process provided by this invention have produced significant and synergistic multiple technical effects, successfully overcoming a series of bottlenecks in the functionality, durability and safety of existing bio-based packaging materials.

[0020] First, the core effect of this invention lies in achieving highly efficient, broad-spectrum, and long-lasting antibacterial performance. By innovatively designing and introducing two functionally complementary modified graphene materials, a multi-dimensional, three-dimensional active antibacterial system is constructed within the film. Specifically, the silver-zinc oxide composite functionalized graphene oxide plays a "rapid elimination" role; its loaded silver nanoparticles effectively release antibacterial ions, interfering with the respiratory chain of microorganisms and damaging cell membranes. Meanwhile, the zinc oxide nanoparticles generate reactive oxygen free radicals under light or humid conditions, killing bacteria through oxidative stress. The synergistic effect of these two components on the graphene carrier significantly enhances immediate antibacterial efficiency. Simultaneously, the quaternized chitosan-grafted reduced graphene oxide plays a "long-lasting protection" role. Its grafted quaternized chitosan long chains carry a large number of cationic groups, which can firmly adsorb negatively charged bacterial cells through electrostatic interactions, disrupting their cell wall integrity. Furthermore, this positively charged antibacterial effect is less likely to induce microbial resistance, thus providing continuous protection. These two mechanisms work together to ensure that the resulting stretch film exhibits near-complete inhibition against common foodborne pathogens, such as Escherichia coli and Staphylococcus aureus, greatly extending the shelf life of packaged fresh food.

[0021] Secondly, this invention demonstrates outstanding performance in significantly improving the overall physical properties of the film, successfully overcoming the inherent defects of traditional bio-based materials, such as insufficient strength and poor barrier properties. Two modified graphene materials, acting as nano-reinforcers, play a crucial skeletal support role in the polymer matrix. In particular, the reduced graphene oxide grafted with quaternized chitosan forms dense hydrogen bonds and physical entanglements between the long polymer chains on its surface and the polyvinyl alcohol and starch molecular chains, greatly improving interfacial compatibility and promoting the uniform dispersion of the nanosheets. This effectively transfers and disperses stress, resulting in a revolutionary enhancement of the film's tensile strength and toughness. Furthermore, the highly dispersed graphene sheets construct a complex, labyrinthine barrier within the matrix, effectively extending the permeation paths of small molecules such as oxygen and water vapor, leading to an order-of-magnitude improvement in the film's gas and water vapor barrier properties. Therefore, the resulting wrapping film is not only flexible and easy to wrap, providing a superior user experience, but also creates a low-oxygen, low-humidity microenvironment for food, physically delaying oxidative rancidity and moisture loss.

[0022] Finally, the technical solution of this invention, while ensuring high performance, embodies the design concepts of green safety and feasibility, and possesses excellent industrialization prospects. The entire preparation process, from the synthesis of modified fillers to the final casting film, primarily uses deionized water as the reaction and dispersion medium, completely eliminating the use of toxic and harmful organic solvents and avoiding the risk of solvent residue migration into food, fully complying with the most stringent safety standards for food contact materials. All raw materials used, including graphite, silver nitrate, chitosan, and various chemical modifiers, are commercially available industrial-grade products with stable sources and controllable costs. The final product uses biodegradable polyvinyl alcohol and starch as the main base materials, and can gradually decompose under the action of microorganisms in the natural environment after disposal, fundamentally solving the "white pollution" problem of traditional plastic packaging. In summary, this invention successfully integrates excellent antibacterial function, superior mechanical barrier properties, reliable safety in use, and environmental friendliness, providing the market with a high-end solution that can practically replace traditional plastic preservation films, with broad application potential in fresh food logistics, retail packaging, and other fields. Detailed Implementation

[0023] The following detailed embodiments are only used to further illustrate this application and should not be construed as limiting the scope of protection of this application. Those skilled in the art can make some non-essential improvements and adjustments to this application based on the above application content.

[0024] Example 1 Preparation of deionized aqueous dispersion of silver-zinc oxide composite functionalized graphene oxide: A 500 mL three-necked flask was filled with 400 mL of a 2 mg / mL graphene oxide (GO) aqueous dispersion. The flask was placed in an ice-water bath, ensuring the bath temperature was maintained at 0°C. An ultrasonic cell disruptor equipped with a 6 mm diameter titanium alloy probe was used, with the output power set to 300 W and the operating mode set to continuous ultrasonication, to sonicate the GO dispersion for 30 min. This process aimed to fully exfoliate the GO sheets, forming a homogeneous and stable dispersion system. After ultrasonication, a mechanical stirrer, thermometer, and nitrogen inlet tube were installed. The mechanical stirrer was turned on, and the stirring speed was set to 300 rpm. Simultaneously, a high-purity nitrogen cylinder was opened, and the nitrogen flow rate was precisely adjusted to 50 mL / min using a pressure reducing valve and flow meter. The nitrogen was introduced into the bottom of the flask and continuously purged for at least 5 min to replace the air inside the flask. Nitrogen gas coverage was maintained throughout the entire reaction process. Under stirring and nitrogen protection, 0.680 g of silver nitrate and 1.190 g of zinc nitrate hexahydrate were weighed using an analytical balance accurate to 0.001 g. Silver nitrate powder was slowly added to the flask through a solid feeding funnel to avoid dust generation; zinc nitrate hexahydrate crystals were then added in the same manner. After the addition was complete, the flask was wrapped with aluminum foil to protect it from light, and the reaction was stirred for 120 min at room temperature (approximately 25°C) to allow the metal ions to be fully adsorbed onto the oxygen-containing functional groups of the GO sheets via electrostatic attraction. Then, the ice-water bath was removed, and the three-necked flask was transferred to a constant-temperature oil bath preheated to 60°C. Once the reaction mixture temperature stabilized at 60°C, 50 mL of a pre-prepared sodium borohydride aqueous solution (0.1 mol / L concentration) stored in ice water at 0°C was slowly added dropwise at a rate of approximately 1 drop / second through a constant-pressure dropping funnel while maintaining rapid stirring at 500 rpm. During the dropwise addition, the system color gradually changed from brownish-black to grayish-black, accompanied by the generation of slight bubbles. After the dropwise addition was complete, the oil bath temperature was maintained at 60℃, and the reaction was stirred for another 300 min. After the reaction was completed, the oil bath was removed, and the reaction mixture was allowed to cool naturally to room temperature. The cooled black suspension was transferred to several 50 mL polypropylene centrifuge tubes and centrifuged at 12000 rpm for 30 min on a high-speed centrifuge. All supernatant was carefully discarded, and the grayish-black solid precipitate at the bottom was collected. 50 mL of deionized water was added to the precipitate, and the mixture was vigorously shaken for 30 s using a vortex mixer to redisperse the precipitate. The mixture was then centrifuged again at 12000 rpm for 30 min, and the supernatant was discarded. This deionized water washing step was repeated 3 times. Subsequently, 50 mL of anhydrous ethanol was used to disperse and centrifuge the precipitate in the same manner. This step was also repeated 3 times to thoroughly remove residual reactants, byproducts, and water. Finally, all the washed solid precipitate was transferred to a 100 mL brown glass sample bottle, and 100 mL of deionized water was added.The sample vials were placed in an ice-water bath and ultrasonically dispersed for 10 minutes at 200W using the aforementioned ultrasonic cell disruptor to obtain a uniform and stable aqueous dispersion of silver-zinc oxide composite functionalized graphene oxide (Ag-ZnO@GO) with a solid content of approximately 2.0%. The dispersion was sealed and stored in a refrigerator at 4°C away from light for later use.

[0025] Preparation of reduced graphene oxide grafted with quaternized chitosan: 2.000 g of chitosan powder with a degree of deacetylation ≥95% was accurately weighed using an analytical balance in a 250 mL single-necked flask. 100 mL of a 2% (w / w) aqueous solution of acetic acid was added to the flask. The flask was placed on a magnetic stirrer with a polytetrafluoroethylene (PTFE) stir bar and stirred overnight (at least 12 h) at 500 rpm at room temperature until the chitosan was completely dissolved, forming a transparent, viscous, and homogeneous solution. 3.000 g of glycidyltrimethylammonium chloride was accurately added to this chitosan solution. The flask was transferred to a 70 °C water bath and reacted for 24 h with continuous stirring (400 rpm). After the reaction was complete, the flask was removed from the water bath. 500 mL of acetone was added to another 1000 mL beaker and stirred on a magnetic stirrer at 200 rpm. The reaction solution was slowly poured into acetone with stirring, and a large amount of white flocculent precipitate was immediately observed to form. After the addition was complete, stirring was continued for 5 minutes, and then the mixture was allowed to stand for 30 minutes to allow complete precipitation. A Buchner funnel and a vacuum filtration flask were assembled, lined with quantitative filter paper, and a vacuum pump was turned on. The entire precipitate mixture was transferred to the funnel for vacuum filtration. The filter cake was washed evenly with 100 mL of anhydrous ethanol three times (approximately 30 mL each time). The washed filter cake was carefully scraped off and transferred to a watch glass, then placed in a vacuum drying oven at 50°C and dried at a vacuum of -0.1 MPa for 24 hours until constant weight. The dried solid was removed and gently ground with an agate mortar to obtain quaternized chitosan (QCS) solid powder, which was then stored in a desiccator for later use. Separately, 100 mL of a 2 mg / mL GO aqueous dispersion was added to a 250 mL three-necked flask. Accurately add 0.500 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and 0.250 g of N-hydroxysuccinimide (NHS). Stir at 300 rpm for 30 min at room temperature to activate the carboxyl groups on the GO surface. Take a 50 mL beaker, accurately weigh 1.000 g of the prepared QCS solid powder, add 50 mL of 2% (w / w) acetic acid aqueous solution, and magnetically stir until completely dissolved. Pour the dissolved QCS solution into the activated GO dispersion. Insert the pH meter electrode into the reaction solution, and while stirring, add 0.5 mol / L sodium hydroxide solution dropwise to precisely adjust the pH of the mixture to 5.5. Install a reflux condenser and continuously purge nitrogen gas (30 mL / min) into the three-necked flask for 15 min to fully displace the air in the system. Then, seal the system under a nitrogen atmosphere. The reaction system was placed in a constant temperature oil bath at 60℃ and stirred at 350 rpm for 780 min (13 h) to carry out the amidation grafting reaction. After the reaction was completed, 0.500 g of ascorbic acid was precisely added to the system.The oil bath temperature was raised to 80℃, and the reaction was continued with stirring at 350 rpm for 420 min (7 h) to achieve simultaneous and mild reduction of GO. During this process, the system color gradually changed from brownish-black to black. After the reaction was completed, the oil bath was removed, and the mixture was allowed to cool naturally to room temperature. The reaction mixture was transferred to a centrifuge tube and centrifuged at 12000 rpm for 20 min. The supernatant was discarded, yielding a black solid precipitate. The precipitate was redispersed with 50 mL of dilute hydrochloric acid solution (pH=4) and centrifuged again. This step was repeated once to remove physically adsorbed QCS. Subsequently, the precipitate was dispersed with 50 mL of deionized water and washed by centrifugation. This step was repeated three times until the washing solution was neutral (pH≈7). The final washed solid precipitate was transferred to a pre-cooled freeze-drying bottle. The sample bottle was placed in a freeze dryer and freeze-dried at a cold trap temperature of -50℃ and a vacuum degree of 10 Pa for 48 h. After drying, a fluffy black quaternized chitosan-grafted reduced graphene oxide (QCS-g-rGO) powder was obtained, which was sealed and stored in a desiccator.

[0026] Preparation of antibacterial bio-graphene food packaging stretch film: Take a 1000mL three-necked flask and install a mechanical stirrer, a spherical condenser, and a thermometer. Add the following to the flask sequentially: 400.0g deionized water, 20.0g glycerol, 70.0g polyvinyl alcohol (PVA, degree of hydrolysis >98%), and 30.0g soluble starch. Place the flask in a 90℃ constant temperature water bath, turn on the mechanical stirrer, and adjust the speed to 300rpm. Continue stirring at this temperature for 210min (3.5h) until the PVA particles are completely dissolved and the starch is fully gelatinized, forming a uniform, transparent, viscous solution without any visible particles or bubbles. Stop heating, remove the water bath, and allow the solution to cool naturally with stirring. When the thermometer shows the solution temperature has dropped to 60℃, pour all the previously prepared Ag-ZnO@GO aqueous dispersion (containing approximately 2.0g of solids) into the three-necked flask at once. Immediately use an IKAT18 high-speed dispersion homogenizer equipped with an S18N-19G dispersion head to perform high-speed shear emulsification of the mixture at 8000 rpm for 300 seconds (5 minutes). Then, accurately weigh 5.0 g of the prepared QCS-g-rGO powder and slowly and evenly sprinkle it into the stirring gel solution through a feeding funnel. After the addition is complete, continue high-speed shearing at 8000 rpm for 600 seconds (10 minutes). Transfer the mixture from the three-necked flask to a 500 mL glass beaker. Prepare a container containing an ice-water mixture, ensuring the bath temperature is 0°C, and place the beaker in the ice-water bath for cooling. Using a Scientz-IID ultrasonic cell disruptor equipped with a 6 mm diameter titanium alloy probe, insert the probe approximately 1 cm below the surface of the mixture. The ultrasonic power was set to 400W, and the working mode was pulse mode (3s operation, 2s interval). The mixture was ultrasonically treated for 900s (15min) to obtain a highly uniform, fine, and fluid composite casting solution. The composite casting solution was poured into a wide-mouth glass petri dish and placed in a vacuum desiccator. The vacuum pump was turned on, and air bubbles were removed from the casting solution at room temperature for 60min. After degassing, a smooth and clean polytetrafluoroethylene (PTFE) casting plate was placed horizontally. The degassed casting solution was poured steadily and slowly onto one end of the casting plate. Using an Elcometer 4340 automatic coating tool, a scraper with a set gap of 1.1mm was selected, and the casting solution was scraped at a constant speed of 10mm / s to form a smooth and uniform wet film. The coated casting plate was carefully moved horizontally into a forced-air drying oven. The oven temperature was set to 35℃, the door was closed, and the plate was dried at this temperature for 1800min (30h). After drying, open the drying oven. The wet film will be fully dried and formed, and will automatically curl and peel off from the upper edge of the PTFE substrate. Carefully peel the entire film off the substrate with tweezers.The peeled film was suspended on a bracket inside a constant temperature and humidity chamber, with the chamber conditions set as follows: temperature 25℃, relative humidity 50%. The film was equilibrated under these conditions for 2880 minutes (48 hours) to allow its internal moisture to reach equilibrium and its performance to stabilize. After equilibration, the final antibacterial bio-graphene food packaging stretch film was obtained.

[0027] Example 2 The specific implementation method is the same as in Example 1, except that the preparation of the deionized aqueous dispersion of silver-zinc oxide composite functionalized graphene oxide is as follows: Take a 500mL three-necked flask and add 400mL of a 2mg / mL graphene oxide (GO) aqueous dispersion. Place the flask in an ice-water bath, ensuring the bath temperature is maintained at 0℃. Use an ultrasonic cell disruptor equipped with a 6mm diameter titanium alloy probe, set the output power to 300W, and the working mode to continuous ultrasonication to sonicate the GO dispersion for 30 minutes. After ultrasonication, install a mechanical stirrer, thermometer, and nitrogen inlet tube. Turn on the mechanical stirrer and set the stirring speed to 300rpm. Simultaneously, open a high-purity nitrogen cylinder and precisely adjust the nitrogen flow rate to 50mL / min using a pressure reducing valve and flow meter, introducing nitrogen into the bottom of the flask and continuously purging for at least 5 minutes to replace the air inside the flask. Then, maintain nitrogen coverage throughout the entire reaction process. Under stirring and nitrogen protection, 0.340 g of silver nitrate and 0.595 g of zinc nitrate hexahydrate were weighed using an analytical balance accurate to 0.001 g. Silver nitrate powder was slowly added to the flask through a solid feeding funnel; zinc nitrate hexahydrate crystals were then added in the same manner. After the addition was complete, the flask was wrapped with aluminum foil to protect it from light, and the reaction was stirred for 120 min at room temperature (approximately 25°C). Then, the ice-water bath was removed, and the three-necked flask was transferred to a constant-temperature oil bath preheated to 60°C. Once the reaction mixture temperature stabilized at 60°C, 25 mL of a pre-prepared sodium borohydride aqueous solution (0.1 mol / L concentration) stored in ice water at 0°C was slowly added dropwise through a constant-pressure dropping funnel at a rate of approximately 1 drop / second, while maintaining rapid stirring at 500 rpm. After the addition was complete, the oil bath temperature was maintained at 60°C, and the reaction was stirred for another 300 min. After the reaction was complete, the oil bath was removed, and the reaction mixture was allowed to cool naturally to room temperature. The cooled black suspension was transferred to multiple 50 mL polypropylene centrifuge tubes and centrifuged at 12,000 rpm for 30 min. All supernatant was carefully discarded, and the grayish-black solid precipitate at the bottom was collected. 50 mL of deionized water was added to the precipitate, and the mixture was vigorously vortexed for 30 s to redisperse the precipitate. The mixture was then centrifuged again at 12,000 rpm for 30 min, and the supernatant was discarded. This deionized water washing step was repeated three times. Subsequently, 50 mL of anhydrous ethanol was used to disperse and centrifuge the precipitate in the same manner, and this step was also repeated three times. Finally, all the washed solid precipitate was transferred to a 100 mL amber glass sample vial, and 100 mL of deionized water was added. The sample vial was placed in an ice-water bath and ultrasonically dispersed at 200 W for 10 min using the aforementioned ultrasonic cell disruptor to obtain a uniform and stable aqueous dispersion of silver-zinc oxide composite functionalized graphene oxide (Ag-ZnO@GO) with a solid content of approximately 1.0%. The dispersion was sealed and stored in a refrigerator at 4°C away from light for later use.

[0028] Preparation of reduced graphene oxide grafted with quaternized chitosan: 2.000 g of chitosan powder with a degree of deacetylation ≥95% was accurately weighed using an analytical balance in a 250 mL single-necked flask. 100 mL of a 2% (w / w) aqueous solution of acetic acid was added to the flask. The flask was placed on a magnetic stirrer with a polytetrafluoroethylene (PTFE) stir bar and stirred overnight (at least 12 h) at 500 rpm at room temperature until the chitosan was completely dissolved. 3.000 g of glycidyltrimethylammonium chloride was accurately added to the chitosan solution. The flask was transferred to a 70 °C water bath and reacted for 24 h with continuous stirring (400 rpm). After the reaction was complete, the flask was removed from the water bath. 500 mL of acetone was added to a 1000 mL beaker and stirred at 200 rpm using a magnetic stirrer. The reaction mixture was slowly poured into the acetone while stirring. After adding the precipitate, continue stirring for 5 minutes, then let it stand for 30 minutes to allow complete precipitation. Assemble the Buchner funnel and vacuum filtration flask, line with quantitative filter paper, turn on the vacuum pump, and transfer the entire precipitate mixture to the funnel for vacuum filtration. Wash the filter cake evenly with 100 mL of anhydrous ethanol three times (approximately 30 mL each time). Carefully scrape off the washed filter cake, transfer it to a watch glass, and place it in a vacuum drying oven at 50°C. Dry it at a vacuum of -0.1 MPa for 24 hours until constant weight. Remove the dried solid and gently grind it with an agate mortar to obtain quaternized chitosan (QCS) solid powder, which is then stored in a desiccator for later use. In a separate 250 mL three-necked flask, add 100 mL of GO aqueous dispersion with a concentration of 2 mg / mL. Accurately add 0.250 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and 0.125 g of N-hydroxysuccinimide (NHS). Stir at 300 rpm for 30 min at room temperature. Take a 50 mL beaker, accurately weigh 0.500 g of the prepared QCS solid powder, add 25 mL of 2% (w / w) acetic acid aqueous solution, and stir magnetically until completely dissolved. Pour the dissolved QCS solution into the activated GO dispersion. Insert the pH meter electrode into the reaction solution, and while stirring, add 0.5 mol / L sodium hydroxide solution dropwise to precisely adjust the pH of the mixture to 5.5. Install a reflux condenser and continuously purge nitrogen gas (30 mL / min) into the three-necked flask for 15 min to fully displace the air in the system. Then seal the system under a nitrogen atmosphere. Place the reaction system in a constant temperature oil bath at 60 °C and stir at 350 rpm for 780 min (13 h). After the reaction is complete, accurately add 0.250 g of ascorbic acid to the system. The oil bath temperature was raised to 80°C, and the reaction was continued with stirring at 350 rpm for 420 min (7 h). After the reaction was completed, the oil bath was removed, and the mixture was allowed to cool naturally to room temperature.The reaction mixture was transferred to centrifuge tubes and centrifuged at 12,000 rpm for 20 min. The supernatant was discarded, yielding a black solid precipitate. The precipitate was redispersed with 50 mL of dilute hydrochloric acid solution (pH=4) and centrifuged again; this step was repeated once. Subsequently, the precipitate was dispersed with 50 mL of deionized water and washed by centrifugation; this step was repeated three times until the washing solution was neutral (pH≈7). The final washed solid precipitate was transferred to a pre-cooled freeze-drying bottle. The sample bottle was placed in a freeze dryer and freeze-dried at a cold trap temperature of -50 °C and a vacuum degree of 10 Pa for 48 h. After drying, quaternary ammonium-modified chitosan-grafted reduced graphene oxide (QCS-g-rGO) powder was obtained, sealed, and stored in a desiccator.

[0029] Preparation of antibacterial bio-graphene food packaging stretch film: Take a 1000mL three-necked flask and install a mechanical stirrer, a spherical condenser, and a thermometer. Add the following to the flask sequentially: 400.0g deionized water, 20.0g glycerol, 60.0g polyvinyl alcohol (PVA, degree of hydrolysis >98%), and 40.0g soluble starch. Place the flask in a 90℃ constant temperature water bath, turn on the mechanical stirrer, and adjust the speed to 300rpm. Continue stirring at this temperature for 210min (3.5h) to form a uniform, transparent, viscous solution without any visible particles or bubbles. Stop heating, remove the water bath, and allow the solution to cool naturally with stirring. When the thermometer shows the solution temperature has dropped to 60℃, pour all the previously prepared Ag-ZnO@GO aqueous dispersion (containing approximately 1.0g of solids) into the three-necked flask at once. Immediately use a high-speed dispersion homogenizer to perform high-speed shear emulsification of the mixture at 8000 rpm for 300 s (5 min). Then, accurately weigh 2.0 g of the prepared QCS-g-rGO powder and slowly and evenly sprinkle it into the stirring gel solution through a feeding funnel. After the addition is complete, continue high-speed shearing at 8000 rpm for 600 s (10 min). Transfer the mixture from the three-necked flask to a 500 mL glass beaker. Prepare a container with an ice-water mixture, ensuring the bath temperature is 0°C, and place the beaker in the ice-water bath for cooling. Using an ultrasonic cell disruptor, insert the probe approximately 1 cm below the surface of the mixture. Set the ultrasonic power to 400 W, the working mode to pulse mode (3 s operation, 2 s interval), and sonicate the mixture for 900 s (15 min) to obtain a homogeneous composite casting solution. Pour the composite casting solution into a wide-mouth glass culture dish and place it in a vacuum desiccator. Turn on the vacuum pump and remove air bubbles from the casting solution at room temperature for 60 minutes. After degassing, take a smooth and clean polytetrafluoroethylene (PTFE) casting plate and place it horizontally. Pour the degassed casting solution smoothly and slowly onto one end of the casting plate. Using an automatic coating tool, select a doctor blade with a set gap of 1.1 mm and coat the casting solution into a smooth and uniform wet film at a constant speed of 10 mm / s. Carefully move the coated casting plate horizontally into a forced-air drying oven, set the oven temperature to 35℃, close the oven door, and dry at this temperature for 1800 minutes (30 hours). After drying, open the drying oven and carefully peel the entire film off the substrate with tweezers. Hang the peeled film on a bracket in a constant temperature and humidity chamber, setting the chamber conditions to: temperature 25℃, relative humidity 50%. Equilibrate the film under these conditions for 2880 minutes (48 hours). After equilibration, the final antibacterial bio-graphene food packaging stretch film is obtained.

[0030] Example 3 The specific implementation method is the same as in Example 1, except that the preparation of the deionized aqueous dispersion of silver-zinc oxide composite functionalized graphene oxide is as follows: Take a 500mL three-necked flask and add 400mL of a 2mg / mL graphene oxide (GO) aqueous dispersion. Place the flask in an ice-water bath, ensuring the bath temperature is maintained at 0℃. Use an ultrasonic cell disruptor equipped with a 6mm diameter titanium alloy probe, set the output power to 300W, and the working mode to continuous ultrasonication to sonicate the GO dispersion for 30 minutes. After ultrasonication, install a mechanical stirrer, thermometer, and nitrogen inlet tube. Turn on the mechanical stirrer and set the stirring speed to 300rpm. Simultaneously, open a high-purity nitrogen cylinder and precisely adjust the nitrogen flow rate to 50mL / min using a pressure reducing valve and flow meter, introducing nitrogen into the bottom of the flask and continuously purging for at least 5 minutes to replace the air inside the flask. Then, maintain nitrogen coverage throughout the entire reaction process. Under stirring and nitrogen protection, 1.360 g of silver nitrate and 2.380 g of zinc nitrate hexahydrate were weighed using an analytical balance accurate to 0.001 g. Silver nitrate powder was slowly added to the flask through a solid feeding funnel; zinc nitrate hexahydrate crystals were then added in the same manner. After the addition was complete, the flask was wrapped with aluminum foil to protect it from light, and the reaction was stirred for 120 min at room temperature (approximately 25°C). Then, the ice-water bath was removed, and the three-necked flask was transferred to a constant-temperature oil bath preheated to 60°C. Once the reaction mixture temperature stabilized at 60°C, 100 mL of a pre-prepared sodium borohydride aqueous solution (0.1 mol / L concentration) stored in ice water at 0°C was slowly added dropwise at a rate of approximately 1 drop / second through a constant-pressure dropping funnel while maintaining rapid stirring at 500 rpm. After the addition was complete, the oil bath temperature was maintained at 60°C, and the reaction was stirred for another 300 min. After the reaction was complete, the oil bath was removed, and the reaction mixture was allowed to cool naturally to room temperature. The cooled black suspension was transferred to several 50 mL polypropylene centrifuge tubes and centrifuged at 12,000 rpm for 30 min. All supernatant was carefully discarded, and the grayish-black solid precipitate at the bottom was collected. 50 mL of deionized water was added to the precipitate, and the mixture was vortexed vigorously for 30 s to redisperse the precipitate. The mixture was then centrifuged again at 12,000 rpm for 30 min, and the supernatant was discarded. This deionized water washing step was repeated three times. Subsequently, 50 mL of anhydrous ethanol was used to disperse and centrifuge the precipitate in the same manner, and this step was also repeated three times. Finally, all the washed solid precipitate was transferred to a 100 mL amber glass sample bottle, and 100 mL of deionized water was added. The sample vials were placed in an ice-water bath and ultrasonically dispersed for 10 minutes at 200W using the aforementioned ultrasonic cell disruptor to obtain a uniform and stable aqueous dispersion of silver-zinc oxide composite functionalized graphene oxide (Ag-ZnO@GO) with a solid content of approximately 3.0%. The dispersion was sealed and stored in a refrigerator at 4°C away from light for later use.

[0031] Preparation of reduced graphene oxide grafted with quaternized chitosan: 2.000 g of chitosan powder with a degree of deacetylation ≥95% was accurately weighed using an analytical balance in a 250 mL single-necked flask. 100 mL of a 2% (w / w) aqueous solution of acetic acid was added to the flask. The flask was placed on a magnetic stirrer with a polytetrafluoroethylene (PTFE) stir bar and stirred overnight (at least 12 h) at 500 rpm at room temperature until the chitosan was completely dissolved. 3.000 g of glycidyltrimethylammonium chloride was accurately added to the chitosan solution. The flask was transferred to a 70 °C water bath and reacted for 24 h with continuous stirring (400 rpm). After the reaction was complete, the flask was removed from the water bath. 500 mL of acetone was added to a 1000 mL beaker and stirred at 200 rpm using a magnetic stirrer. The reaction mixture was slowly poured into the acetone while stirring. After adding the precipitate, continue stirring for 5 minutes, then let it stand for 30 minutes to allow complete precipitation. Assemble the Buchner funnel and vacuum filtration flask, line with quantitative filter paper, turn on the vacuum pump, and transfer the entire precipitate mixture to the funnel for vacuum filtration. Wash the filter cake evenly with 100 mL of anhydrous ethanol three times (approximately 30 mL each time). Carefully scrape off the washed filter cake, transfer it to a watch glass, and place it in a vacuum drying oven at 50°C. Dry it at a vacuum of -0.1 MPa for 24 hours until constant weight. Remove the dried solid and gently grind it with an agate mortar to obtain a white, fluffy quaternized chitosan (QCS) solid powder, which is then stored in a desiccator for later use. In a separate 250 mL three-necked flask, add 100 mL of GO aqueous dispersion with a concentration of 2 mg / mL. Accurately add 1.000 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and 0.500 g of N-hydroxysuccinimide (NHS). Stir at 300 rpm for 30 min at room temperature. Accurately weigh 2.000 g of the prepared QCS solid powder into a 50 mL beaker, add 50 mL of 2% (w / w) acetic acid aqueous solution, and stir magnetically until completely dissolved. Pour the dissolved QCS solution into the activated GO dispersion. Insert the pH meter electrode into the reaction solution, and while stirring, add 0.5 mol / L sodium hydroxide solution dropwise to precisely adjust the pH of the mixture to 5.5. Install a reflux condenser and continuously purge nitrogen gas (30 mL / min) into the three-necked flask for 15 min to fully displace the air in the system. Then seal the system under a nitrogen atmosphere. Place the reaction system in a constant temperature oil bath at 60 °C and stir at 350 rpm for 780 min (13 h). After the reaction is complete, accurately add 1.000 g of ascorbic acid to the system. The oil bath temperature was raised to 80°C, and the reaction was continued with stirring at 350 rpm for 420 min (7 h). After the reaction was completed, the oil bath was removed, and the mixture was allowed to cool naturally to room temperature.The reaction mixture was transferred to centrifuge tubes and centrifuged at 12,000 rpm for 20 min. The supernatant was discarded, yielding a black solid precipitate. The precipitate was redispersed with 50 mL of dilute hydrochloric acid solution (pH=4) and centrifuged again; this step was repeated once. Subsequently, the precipitate was dispersed with 50 mL of deionized water and washed by centrifugation; this step was repeated three times until the washing solution was neutral (pH≈7). The final washed solid precipitate was transferred to a pre-cooled freeze-drying bottle. The sample bottle was placed in a freeze dryer and freeze-dried at a cold trap temperature of -50 °C and a vacuum degree of 10 Pa for 48 h. After drying, a fluffy black quaternized chitosan-grafted reduced graphene oxide (QCS-g-rGO) powder was obtained, which was sealed and stored in a desiccator.

[0032] Preparation of antibacterial bio-graphene food packaging stretch film: Take a 1000mL three-necked flask and install a mechanical stirrer, a spherical condenser, and a thermometer. Add the following ingredients to the flask in sequence: 400.0g deionized water, 20.0g glycerol, 80.0g polyvinyl alcohol (PVA, degree of hydrolysis >98%), and 20.0g soluble starch. Place the flask in a 90℃ constant temperature water bath, turn on the mechanical stirrer, and adjust the speed to 300rpm. Continue stirring at this temperature for 210min (3.5h) to form a uniform, transparent, viscous solution without any visible particles or bubbles. Stop heating, remove the water bath, and allow the solution to cool naturally with stirring. When the thermometer shows that the solution temperature has dropped to 60℃, pour all the previously prepared Ag-ZnO@GO aqueous dispersion (containing approximately 3.0g of solids) into the three-necked flask at once. Immediately use a high-speed dispersion homogenizer to perform high-speed shear emulsification of the mixture at 8000 rpm for 300 s (5 min). Then, accurately weigh 8.0 g of the prepared QCS-g-rGO powder and slowly and evenly sprinkle it into the stirring gel solution through a feeding funnel. After the addition is complete, continue high-speed shearing at 8000 rpm for 600 s (10 min). Transfer the mixture from the three-necked flask to a 500 mL glass beaker. Prepare a container with an ice-water mixture, ensuring the bath temperature is 0°C, and place the beaker in the ice-water bath for cooling. Using an ultrasonic cell disruptor, insert the probe approximately 1 cm below the surface of the mixture. Set the ultrasonic power to 400 W, the working mode to pulse mode (3 s operation, 2 s interval), and sonicate the mixture for 900 s (15 min) to obtain a homogeneous composite casting solution. Pour the composite casting solution into a wide-mouth glass culture dish and place it in a vacuum desiccator. Turn on the vacuum pump and remove air bubbles from the casting solution at room temperature for 60 minutes. After degassing, take a smooth and clean polytetrafluoroethylene (PTFE) casting plate and place it horizontally. Pour the degassed casting solution smoothly and slowly onto one end of the casting plate. Using an automatic coating tool, select a doctor blade with a set gap of 1.1 mm and coat the casting solution into a smooth and uniform wet film at a constant speed of 10 mm / s. Carefully move the coated casting plate horizontally into a forced-air drying oven, set the oven temperature to 35℃, close the oven door, and dry at this temperature for 1800 minutes (30 hours). After drying, open the drying oven and carefully peel the entire film off the substrate with tweezers. Hang the peeled film on a bracket in a constant temperature and humidity chamber, setting the chamber conditions to: temperature 25℃, relative humidity 50%. Equilibrate the film under these conditions for 2880 minutes (48 hours). After equilibration, the final antibacterial bio-graphene food packaging stretch film is obtained.

[0033] Comparative Example 1 The specific implementation method is the same as in Example 1, except that the deionized water dispersion of silver-zinc oxide composite functionalized graphene oxide and the reduced graphene oxide grafted with quaternized chitosan are not added. The preparation process is as follows: In a 1000mL three-necked flask, 400.0g of deionized water, 20.0g of glycerol, 70.0g of polyvinyl alcohol and 30.0g of soluble starch are added. The flask is placed in a 90℃ water bath and stirred continuously at 300rpm for 3.5h to form a uniform gel. After cooling to 60℃, only high-speed shearing (8000rpm, for 5min) and ice-water bath ultrasonic treatment (400W, for 5min) are performed. Then, following the exact same parameters and steps as in Example 1, vacuum degassing is performed for 1h, casting is performed on a polytetrafluoroethylene plate, the film thickness is 1.1mm, drying is performed at 35℃ for 30h, the film is peeled off, and equilibration is carried out at 25℃ and 50% humidity for 48h to obtain a pure biopolymer film.

[0034] Comparative Example 2 The specific implementation method is the same as in Example 1, except that this comparative example only adds a deionized aqueous dispersion of silver-zinc oxide composite functionalized graphene oxide, without adding quaternized chitosan-grafted reduced graphene oxide. The preparation process is as follows: A deionized aqueous dispersion of silver-zinc oxide composite functionalized graphene oxide is prepared according to the method in Example 1. A polymer solution is prepared according to the method in Example 1, i.e., 400.0 g of deionized water, 20.0 g of glycerol, 70.0 g of polyvinyl alcohol, and 30.0 g of soluble starch are added to a 1000 mL three-necked flask, stirred at 90°C for 3.5 h, and then cooled to 60°C. The modified dispersion is then completely added to the 60°C solution, and emulsified at 8000 rpm for 5 min using high-speed shearing. Without adding a second filler, it is directly transferred to an ice-water bath and treated with 400 W pulsed ultrasonication for 15 min. All subsequent degassing, casting, film thickness setting (1.1 mm), drying, and equilibration process parameters are exactly the same as in Example 1.

[0035] Comparative Example 3 The specific implementation method is the same as in Example 1, except that this comparative example only adds quaternary ammonium-modified chitosan-grafted reduced graphene oxide, without adding a deionized water dispersion of silver-zinc oxide composite functionalized graphene oxide. The preparation process is as follows: 5.0 g of quaternary ammonium-modified chitosan-grafted reduced graphene oxide powder is prepared according to the method in Example 1. A polymer solution is prepared according to the method in Example 1, i.e., 400.0 g of deionized water, 20.0 g of glycerol, 70.0 g of polyvinyl alcohol, and 30.0 g of soluble starch are added to a 1000 mL three-necked flask, stirred at 90°C for 3.5 h, and then cooled to 60°C. Without adding the first filler, 5.0 g of quaternary ammonium-modified chitosan-grafted reduced graphene oxide powder is directly added to the 60°C solution, sheared at 8000 rpm for 10 min, and then transferred to an ice-water bath for pulsed ultrasonic treatment at 400 W power for 15 min. All subsequent degassing, casting, film thickness of 1.1 mm, drying, and balancing process parameters are exactly the same as in Example 1.

[0036] Performance testing The antibacterial bio-graphene food packaging stretch films prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to the following method, which included the following steps: The antibacterial performance was tested using the film-coverage quantitative method. The films obtained in each example and comparative example were wiped with 75% ethanol in a sterile operating table, and then sterilized on both sides by irradiation under a UV lamp for 30 minutes. The films were then cut into 50.0 mm × 50.0 mm square samples using a sterile mold. 0.4 mL of the solution was taken and adjusted to a concentration of 1.0 × 10⁻⁶. 5A CFU / mL suspension of *Escherichia coli* and a suspension of *Staphylococcus aureus* were evenly spread onto the surface of a sterile membrane sample. Immediately, another sterile polyethylene membrane of the same size was placed over the sample and gently pressed to ensure complete encapsulation of the bacterial suspension between the two membranes, creating a tight contact. The inoculated sample was placed in a sterile petri dish and incubated in a constant temperature and humidity incubator at 37.0℃ and a relative humidity greater than 90% for 24.0 h. After incubation, each pair of membrane samples was transferred to a homogenizer bag containing 20.0 mL of sterile phosphate-buffered saline (PBS, 0.1 mol / L, pH 7.2) and vigorously shaken for 2.0 min using a shaker to thoroughly elute the bacteria. A suitable amount of eluent was serially diluted 10-fold, and 100.0 μL of each diluted sample was plated on nutrient agar plates, with three replicates for each dilution. After coating, the plates were incubated upside down at 37.0℃ for 24.0 h, and then colony counting was performed. The antibacterial rate was calculated using the formula: Antibacterial rate = [(average colony count of control group - average colony count of experimental group) / average colony count of control group] × 100%. A pure polymer film without any added functional fillers (Comparative Example 1) was used as a positive control group. Each sample was tested 5 times, and the results were taken as the arithmetic mean.

[0037] Mechanical property testing employed a tensile test method. Each film was conditioned for at least 48 hours in a standard environment at 23.0℃±2.0℃ and 50%±5% relative humidity. The film was cut into specimens of the specified shape using a standard dumbbell-shaped cutter (e.g., ASTM D638 Type V), with a gauge length width of 6.0 mm and a total length not less than 60.0 mm. The thickness was measured at five points uniformly within the gauge length using a digital thickness gauge, and the average value was taken as the specimen thickness. The specimen was mounted in the pneumatic clamp of a universal testing machine, ensuring the longitudinal axis of the specimen was aligned with the direction of the tensile force, and the initial clamping distance was set to 25.0 mm. Tension was applied at a constant beam speed of 500 mm / min until the specimen broke. The testing system automatically recorded the load-displacement curve and calculated the tensile strength (unit: MPa) and elongation at break (unit: %) based on the curve data. Tensile strength was calculated by dividing the maximum load by the initial minimum cross-sectional area of ​​the specimen; elongation at break was calculated by dividing the elongation of the gauge length at break by the original gauge length. At least 8 valid samples were tested for each group of films. After removing outliers, the average value and standard deviation were calculated.

[0038] Oxygen permeability testing employed the isobaric method (coulometric method). The membrane was cut into circular samples with a diameter of 100.0 mm and mounted on the test chamber, ensuring the samples were flat and wrinkle-free. Test conditions were set as follows: temperature 23.0℃ ± 0.5℃, relative humidity 0% (i.e., using dry carrier gas). High-purity nitrogen was introduced as the carrier gas on one side of the test chamber, while oxygen flowed on the other side. The instrument accurately detected the amount of oxygen permeating the membrane using a coulometric sensor. Once the system reached a stable permeation state, the instrument automatically calculated and output the oxygen permeability value, expressed in cubic centimeters per square meter per 24 hours per standard atmosphere. At least three parallel samples were tested for each specimen, and the average result was taken.

[0039] The water vapor transmission rate was tested using the weight gain method (cup method). An appropriate amount of anhydrous calcium chloride desiccant (dried to constant weight at 105℃) was evenly spread at the bottom of the permeation cup, filling to a height not exceeding half the cup depth. A circular sample, cut from a film with a diameter larger than the cup opening, was placed over the opening and securely fastened with a sealing ring and cap to ensure a good seal. The assembled permeation cup was accurately weighed on an analytical balance (initial mass M0), and then placed in a constant temperature and humidity chamber under the following conditions: temperature 38.0℃ ± 0.5℃, relative humidity 90% ± 2%. At regular intervals (e.g., 24.0 hours), the permeation cup was removed, quickly cooled to room temperature in a desiccator, and its mass was accurately measured and recorded as M. n Continuous weighing continues until the mass increment shows a stable linear relationship with time. Water vapor transmission rate is calculated as the mass increment per unit area per unit time, in g / (m²). 2 •d). Prepare at least 3 parallel permeation cups for each sample for testing.

[0040] Silver migration was measured using a food simulant immersion method. A 4% (w / w) aqueous solution of acetic acid was used as the acidic food simulant. The film was cut into pieces with a total surface area of ​​1.00 dm². 2 The sample (double-sided calculation) was completely immersed in a chemically inert container (such as a glass conical flask) containing 100.0 mL of the simulant. Ensure the sample was completely submerged in the simulant and free of air bubbles. After sealing the container, it was placed in a constant-temperature shaking water bath at 40.0℃±1.0℃ and continuously shaken at 60 r / min for 24.0 h±0.5 h. After immersion, the simulant was removed, and if necessary, filtered or centrifuged to remove any detached particles. The silver content in the simulant immersion solution was quantitatively analyzed using inductively coupled plasma mass spectrometry (ICP-MS). The concentration of silver in the migration solution was calculated using a calibration curve and converted to the migration amount per unit area (mg / dm²) based on the sample area and simulant volume. A blank control experiment was also performed.

[0041] Test results: Table 1: Test results of each embodiment and comparative example ; As can be seen from Table 1, Examples 1-3 of the present invention systematically solve the key bottlenecks of biodegradable food packaging films in the prior art compared with Comparative Examples 1-3.

[0042] Specifically, the test data of Comparative Example 1 (pure bio-based membrane) clearly exposes the inherent defects of the unmodified material: its tensile strength is only 35.2 MPa, and its oxygen and water vapor permeability are as high as 220.5 cm⁻¹. 3 / (m 2 ·d·atm) and 950g / (m 2 •d) Furthermore, it lacks antibacterial ability (antibacterial rate less than 5%), confirming its fundamental problems of weak mechanical strength, poor barrier properties, and lack of functionality. The data from Comparative Example 2 (only Ag-ZnO@GO added) and Comparative Example 3 (only QCS-g-rGO added) reveal the limitations of a single functionalization strategy: Comparative Example 2, while exhibiting high antibacterial rates (99.65% and 99.30%), has a tensile strength of only 55.1 MPa. Although its barrier properties are improved, they remain unsatisfactory, and its silver migration is relatively high (0.15 mg / kg), indicating its inadequacy in improving mechanical and barrier properties and ensuring stable metal ion fixation. Comparative Example 3 shows a significant improvement in mechanical properties (tensile strength 72.4 MPa), but its antibacterial performance is relatively weak (96.20% and 95.50%), reflecting the shortcomings of single organic modification in providing potent and immediate antibacterial capabilities.

[0043] In stark contrast, Examples 1-3 achieved comprehensive and significant performance optimization through the synergistic introduction of two modified materials. Particularly in the optimal Example 1, the antibacterial rate against both *Escherichia coli* and *Staphylococcus aureus* exceeded 99.99%, achieving near-complete sterilization and solving the problem of single or inefficient antibacterial function; the tensile strength was significantly increased to 86.5 MPa, while the oxygen and water vapor permeability were significantly reduced to 18.5 cm⁻¹. 3 / (m 2 ·d·atm) and 125g / (m 2 •d) effectively overcomes the defects of poor mechanical and barrier properties, and can create a more effective protective barrier for food.

[0044] More importantly, while achieving the aforementioned high performance, the silver migration amount in Example 1 was strictly controlled to below 0.01 mg / kg, which is far below the safety standard limit. This proves that by co-compositing silver nanoparticles with zinc oxide on graphene sheets and then synergizing with the grafting network of quaternized chitosan, functional nanoparticles can be greatly stabilized and their migration into food can be effectively prevented. This successfully solves the core contradiction of the difficulty in balancing high performance and green food safety.

[0045] Therefore, the test data fully confirms that the technical solution of the present invention, through the innovative design and synergistic application of two modified graphene materials, not only endows the film with excellent and long-lasting broad-spectrum antibacterial activity, but also significantly enhances its mechanical strength and gas barrier properties, and ensures extremely high safety in use, thereby comprehensively meeting the multiple requirements of efficient functionalization, durability and safety of packaging materials for fresh food preservation.

[0046] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A preparation process for an antibacterial bio-graphene food packaging stretch film, characterized by the following steps: include: S1. By weight, add 60-80 parts of polyvinyl alcohol and 20-40 parts of starch to a three-necked flask containing a mixed solvent of 400-600 parts of deionized water and 15-25 parts of glycerol. Stir continuously in a water bath at 88-92℃ and cool to 58-62℃ to obtain a gel. Add a deionized water dispersion containing 0.5-3.0 parts of silver-zinc oxide composite functionalized graphene oxide to the gel and shear emulsify. Add 2.0-8.0 parts of quaternary ammonium salted chitosan-grafted reduced graphene oxide, continue shearing, and then transfer to an ice-water bath for ultrasonic treatment to obtain a composite casting solution. S2. Vacuum degas the composite casting liquid and then pour it onto a polytetrafluoroethylene (PTFE) casting plate. Use a scraper to control the thickness of the wet film. Place the PTFE casting plate in a forced-air drying oven and dry it at a constant temperature of 34-36℃. After the wet film is formed, peel it off from the substrate to obtain a thin film. Place the thin film at 24-26℃ to equilibrate.

2. The preparation process of the antibacterial bio-graphene food packaging stretch film according to claim 1, characterized in that, In step S1, the stirring time in a water bath at 88-92℃ is 3-4 hours.

3. The preparation process of the antibacterial bio-graphene food packaging stretch film according to claim 1, characterized in that, In step S2, the drying time at a constant temperature of 34-36℃ is 24-36 hours.

4. The preparation process of the antibacterial bio-graphene food packaging stretch film according to claim 1, characterized in that, The preparation method of the deionized aqueous dispersion of the silver-zinc oxide composite functionalized graphene oxide includes: A1. The deionized aqueous dispersion of graphene oxide was ultrasonically treated in an ice-water bath; under stirring and nitrogen protection, silver nitrate and zinc nitrate hexahydrate were added to obtain a mixture; the mixture was heated to 58-62℃, and pre-cooled sodium borohydride aqueous solution was added dropwise under stirring, and the reaction was continued at 58-62℃ to obtain a reaction mixture. A2. Cool the reaction mixture to room temperature, centrifuge to obtain a solid precipitate, wash the solid precipitate alternately with deionized water and anhydrous ethanol to obtain a washed solid precipitate; redisperse the washed solid precipitate in deionized water.

5. The preparation process of the antibacterial bio-graphene food packaging stretch film according to claim 4, characterized in that, In step A1, the reaction continues at 58-62℃ for 4-6 hours.

6. The preparation process of the antibacterial bio-graphene food packaging stretch film according to claim 4, characterized in that, In step A2, the centrifugation time is 20-40 minutes.

7. The preparation process of the antibacterial bio-graphene food packaging stretch film according to claim 1, characterized in that, The preparation method of the quaternary ammonium salt-treated chitosan-grafted reduced graphene oxide includes: B1. Chitosan was dissolved in an aqueous acetic acid solution, glycidyltrimethylammonium chloride was added, and the mixture was stirred in a water bath at 68-72℃ to obtain a reaction solution. The reaction solution was precipitated with acetone, filtered, washed with ethanol, and vacuum dried to obtain quaternized chitosan solid. A deionized aqueous dispersion of graphene oxide was added to 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide and activated at room temperature. Quaternized chitosan solid dissolved in acetic acid solution was added, and the pH was adjusted to 5.4-5.6 with sodium hydroxide solution. The mixture was stirred in a nitrogen atmosphere at 58-62℃ to obtain an intermediate mixture. B2. Add ascorbic acid to the intermediate mixture and continue the reaction at 78-82℃ to obtain a reaction mixture; centrifuge the reaction mixture to obtain a solid precipitate, wash the solid precipitate with dilute hydrochloric acid and deionized water, and freeze-dry it.

8. The preparation process of the antibacterial bio-graphene food packaging stretch film according to claim 7, characterized in that, In step B1, the reaction is carried out under a nitrogen atmosphere at 58-62°C for 12-14 hours with stirring.

9. The preparation process of the antibacterial bio-graphene food packaging stretch film according to claim 7, characterized in that, In step B2, the reaction continues at 78-82℃ for 6-8 hours.

10. An antibacterial bio-graphene food packaging stretch film, characterized in that, The antibacterial bio-graphene food packaging stretch film is prepared according to any one of claims 1-9.