Preparation method of food plastic packaging bag

Abstract

The invention discloses a preparation method of a food plastic packaging bag in the field of food packaging materials, and the method comprises the following steps: firstly, preparing a magnesium lithium silicate zinc oxide heterostructure nanorod inorganic modified material through a multi-step reaction, and carrying out hydrothermal synthesis on magnesium lithium silicate nanosheets in an inert atmosphere; the preparation method comprises the following steps: curling into a hollow nanorod under the guidance of a surfactant, carrying out silver ion functionalization, then growing zinc oxide nanocrystals on the surface in situ to form a heterostructure, and finally carrying out high-temperature calcination crystallization and steam hydrophobization treatment to obtain a final product. The modified material is dispersed in a homogenized bacterial cellulose nanofiber suspension according to a small proportion, and the food packaging bag is prepared after blending, film casting, staged drying and low-temperature hot pressing. The packaging bag prepared through the method has high strength, high barrier property, excellent hydrophobicity and antibacterial activity, the shelf life of food is effectively prolonged, the technology is simple, raw materials are environmentally friendly, and the packaging bag is suitable for large-scale production.

Description

Technical Field

[0001] This invention relates to the field of food packaging materials technology, and specifically to a method for preparing food plastic packaging bags. Background Technology

[0002] With increasing global focus on environmental protection and food safety, the "white pollution" and limited functionality of traditional petroleum-based plastic packaging materials have become increasingly prominent. This has prompted research and industry to turn their attention to renewable bio-based materials, aiming to develop green packaging alternatives that can degrade in the natural environment and reduce fossil resource consumption. Among numerous candidate materials, bacterial cellulose, produced by microbial fermentation, shows great application potential due to its unique nanofiber network structure, high crystallinity, excellent mechanical strength, good biocompatibility, and biodegradability. However, despite its promising prospects, key drawbacks of bacterial cellulose materials, such as inherent strong hydrophilicity, lack of active antibacterial function, and the need for further improvement in gas barrier properties, severely restrict its direct application in high-standard food preservation packaging. Therefore, how to effectively modify it to retain its green nature while endowing it with comprehensive and superior packaging performance has become the main direction for current technological breakthroughs.

[0003] Currently, research on the modification of bacterial cellulose mainly focuses on the construction of its functionalized composite materials. Common technical approaches involve introducing various inorganic or organic functional fillers into its three-dimensional network structure. For example, incorporating mineral nanoclays to improve mechanical and barrier properties, or adding metal oxide nanoparticles to achieve antibacterial activity. However, these conventional modification methods often face numerous challenges. On the one hand, simple physical blending easily leads to uneven dispersion and aggregation of nanofillers in the hydrophilic cellulose matrix. This not only weakens the reinforcing effect of the fillers but may also cause stress defects within the material, affecting the uniformity and stability of performance. On the other hand, most modification strategies can only achieve limited improvements to a specific property; for example, improving strength but sacrificing toughness, or increasing antibacterial properties but failing to simultaneously optimize the barrier effect against water vapor and oxygen. More importantly, achieving substantial performance improvements usually requires high filler addition levels, which may impair the light transmittance and flexibility of the bacterial cellulose film and increase production costs. Therefore, developing a novel modified material that can produce a strong synergistic effect with bacterial cellulose matrix and achieve multifunctional integration with low addition amount is the key to promoting the practical application of high-performance bio-based packaging.

[0004] To address the aforementioned technical bottlenecks, this invention aims to provide a fundamental solution. Its core lies in designing and preparing a novel, functionally integrated inorganic modified material. This material, through sophisticated chemical structure and interface design, can perfectly embed and strengthen bacterial cellulose networks. This invention not only focuses on improving individual properties but also strives to simultaneously and significantly enhance the mechanical strength, water and oxygen barrier properties, hydrophobicity, and broad-spectrum antibacterial activity of the composite material using an innovative modifier. Simultaneously, this invention emphasizes the feasibility of production practice, ensuring a scientifically rigorous and readily available preparation path for the core modified material. The final composite film processing technology strives for simplicity, efficiency, and good compatibility with existing production conditions, thereby paving the way from laboratory innovation to industrial application and providing the market with a truly next-generation food packaging material that combines superior performance, environmental friendliness, and practical value. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing food plastic packaging bags, which solves the technical problem that existing food packaging materials cannot simultaneously achieve high barrier properties, strong antibacterial activity and excellent mechanical properties, and the comprehensive modification process is complicated.

[0006] The present invention achieves the above objectives through the following technical solutions: A method for preparing a food plastic packaging bag includes the following steps: S1, by weight, 80-120 parts of bacterial cellulose membrane are washed with deionized water until neutral to obtain washed bacterial cellulose membrane. The washed bacterial cellulose membrane is mixed with 9800-9900 parts of deionized water and placed in a homogenizer for homogenization to obtain bacterial cellulose nanofiber suspension. S2, 1.5-5.0 parts of magnesium lithium silicate-zinc oxide heterostructured nanorods are dispersed in 50-100 parts of anhydrous ethanol and ultrasonically treated to obtain a suspension; the suspension is added to the bacterial cellulose nanofiber suspension under stirring and stirring is continued to obtain a blended slurry; S3, the blended slurry is subjected to vacuum degassing treatment, and the slurry is cast onto a polyethylene terephthalate substrate to obtain a coated substrate; the coated substrate is transferred to a drying oven and dried at 38-42℃, and then dried at 58-62℃ to obtain a dried film; S4. Place the dried film in a flat vulcanizing machine and hot-press it at 78-82℃. After hot pressing, cut and roll it up.

[0007] In this invention, when the lithium magnesium silicate-zinc oxide heterostructure nanorods are used to prepare food packaging bags, their mechanism of action is manifested in the synergistic effect across the entire chain, from nanoscale dispersion to macroscopic performance. In the blending and compounding stage, the ultrasonically pre-dispersed nanorods are introduced into an aqueous suspension of bacterial cellulose nanofibers through mechanical stirring. The modified hydrophobic and partially hydrophilic groups on the nanorod surface, along with the zinc ion sites provided by zinc oxide, can generate strong hydrogen bonding, van der Waals forces, and even coordination bonds with the abundant hydroxyl and ether bonds on the bacterial cellulose fibers. This multi-layered and strong interfacial bonding ensures that the nanorods do not agglomerate or separate during subsequent processing, but rather act as ultra-strong nano-reinforcements, uniformly interwoven and anchored within the three-dimensional nanofiber network. This is fundamental to the composite material's superior mechanical strength. In the casting and drying stages, as moisture evaporates, the bacterial cellulose fibers approach and tightly bind to each other under capillary forces, while the dispersed nanorods undergo a certain degree of orientation alignment under fluid shear and interfacial tension. This process constructs a unique "brick-and-mortar" composite structure in situ within the film. Highly oriented nanorods with a large aspect ratio act as the "bricks," while the flexible bacterial cellulose nanofiber network serves as the "mortar," filling and binding the structure. This dense microstructure significantly extends the tortuous paths that water and oxygen molecules must traverse to diffuse within the material, creating a pronounced "maze effect"—the core physical mechanism behind the packaging bag's extremely high barrier properties. Simultaneously, the persistent hydrophobic layer on the nanorod surface forms a low-energy barrier on the composite material surface, synergistically enhancing the material's overall resistance to water vapor permeation. Finally, the low-temperature hot-pressing process not only further eliminates micro-defects within the film and improves density but also, through the combined effect of heat and pressure, further strengthens the interfacial bonding between the bacterial cellulose fibers and nanorods, making stress transfer more efficient. In terms of antibacterial function, silver ions loaded into the inner cavity of the nanorods provide a sustained-release, contact-based ionic antibacterial effect; while the zinc oxide heterostructures constructed on the surface can generate reactive oxygen free radicals under light conditions, exerting highly efficient photocatalytic antibacterial efficacy; the combination of these two with the biocompatibility of bacterial cellulose itself endows the packaging material with a multi-modal, synergistically enhanced intelligent antibacterial property. Therefore, the final food packaging bag is not a product of simple component superposition, but rather a high-performance transformation from nano-functional units to macroscopic practical products achieved through ingenious interface design and multi-level structural control, comprehensively exhibiting mechanical, barrier, and active preservation capabilities that surpass those of traditional materials.

[0008] According to a preferred embodiment of the present invention, the homogenization time in step S1 is 5-10 min.

[0009] According to a preferred embodiment of the present invention, in step S2, the stirring time is 2-4 hours.

[0010] According to a preferred embodiment of the present invention, in step S3, the drying time at 38-42°C is 12-14 hours.

[0011] According to a preferred embodiment of the present invention, in step S4, the hot pressing treatment at 78-82°C takes 2-4 minutes.

[0012] According to a preferred embodiment of the present invention, the preparation steps of the lithium magnesium silicate-zinc oxide heterostructure nanorods include: A1, by weight, under argon protection, 80-120 parts of magnesium nitrate hexahydrate and 104-110 parts of tetraethyl orthosilicate were dissolved in a mixed solvent of 800-1200 parts of anhydrous ethanol and 200-300 parts of deionized water. While stirring, an ethanol solution of lithium hydroxide was added dropwise to adjust the pH to 10.4-10.6, resulting in a gel. The gel was transferred to a high-pressure reactor and subjected to hydrothermal reaction at 175-185℃. After the reaction, the mixture was naturally cooled to room temperature, and the precipitate was collected by centrifugation. The precipitate was washed alternately with ethanol and deionized water to obtain the product. The product was redispersed in deionized water and ultrasonically treated in an ice-water bath to obtain a colloidal dispersion of lithium magnesium silicate nanosheets. A2. The colloidal dispersion of lithium magnesium silicate nanosheets was transferred to a three-necked flask, heated to 84-86℃ and stirred. Hexadecyltrimethylammonium bromide aqueous solution was added, and the reaction was continued with stirring. The nanorods were collected by centrifugation and washed with deionized water at 60-80℃ to obtain washed nanorods. The washed nanorods were redispersed in deionized water, and silver nitrate solution was added under light-protected conditions. The reaction was stirred at 58-62℃. After the reaction was completed, the precipitate was separated by centrifugation and washed with deionized water to obtain the silver-loaded lithium magnesium silicate nanorod primary product. A3. The silver-loaded lithium magnesium silicate nanorods were redispersed in a mixed solvent of ethylene glycol and dimethyl sulfoxide to obtain a suspension. Under nitrogen protection and heating in a water bath at 64-66°C, a zinc acetate ethylene glycol solution and a dimethyl aminoethanol dimethyl sulfoxide solution were added dropwise to the suspension. After the addition was complete, the temperature was raised to 84-86°C for further aging. After the reaction was completed, the solid was collected by centrifugation and washed with N,N-dimethylformamide and anhydrous ethanol to obtain the washed solid. A4. The washed solid is placed in a tube furnace and calcined at 445-455℃ in an air atmosphere. After calcination, it is naturally cooled to 180-190℃ to obtain powder. The powder is transferred to a glove box filled with nitrogen and cooled to room temperature to obtain cooled powder. The cooled powder is placed in a vacuum dryer and hexamethyldisilazane vapor is introduced. The vacuum dryer is placed in an oven at 70-80℃ for treatment. After treatment, it is dried in a vacuum drying oven at 78-82℃.

[0013] In this invention, the preparation of the lithium magnesium silicate and zinc oxide heterostructure nanorods is a multi-stage chemical process based on precise molecular design and stepwise controllable assembly. Its core mechanism lies in constructing composite nanomaterials with specific topologies and multiple functions through sequential reactions. In the first stage, namely the synthesis and structure establishment of the precursors, magnesium and silicon sources undergo hydrolysis and condensation reactions in an alcohol-water mixed solvent under an inert atmosphere, forming an amorphous gel network rich in silanol groups and magnesium-oxygen bonds under alkaline conditions. Subsequently, through a high-temperature, high-pressure hydrothermal process, this amorphous network undergoes directional recrystallization, driving the orderly arrangement and layer-by-layer stacking of silicon-oxygen tetrahedra and magnesium-oxygen octahedra, ultimately forming well-crystallized layered lithium magnesium silicate. Intense ultrasonic treatment utilizes cavitation energy to overcome interlayer forces, exfoliating it into nanosheets rich in active silanol groups on the surface, laying the foundation for subsequent structural evolution. The second stage, morphology guidance and initial functionalization, involves the introduction and adsorption of surfactant molecules onto the nanosheet surface. Due to their differentiated modification of the anisotropic sheet edges and planes, the planar stability of the sheets is reduced. Driven by the thermal energy provided by continuous heating and stirring, the sheets spontaneously curl around a specific direction to reduce the total energy of the system, eventually closing to form hollow nanorod structures with one or both ends open. After this step, the template agent is thoroughly removed by washing, exposing the clean inner and outer surfaces of the rods. Subsequently, under light-protected and mildly heated conditions, silver ions are stably immobilized in the inner channels and interlayer domains of the nanorods through ion exchange with the interlayer and surface hydroxyl groups of lithium magnesium silicate, as well as electrostatic adsorption, achieving the initial implantation of antibacterial function. The third stage, heterogeneous epitaxial growth, is crucial for achieving heterogeneous nucleation and controllable growth of zinc oxide on the formed nanorod substrate. The functionalized nanorods are dispersed in a high-boiling-point organic solvent, and zinc salts and organic bases are simultaneously added under an inert atmosphere and precise temperature control. Organic bases gradually release hydroxide ions, which combine with zinc ions to form zinc hydroxyl complexes. These complexes preferentially adsorb and undergo dehydration condensation at defects, edges, or specific active sites on the nanorod surface, forming zinc oxide nuclei. By strictly controlling the reaction kinetics, the nuclei grow epitaxially or radially along the nanorods, rather than precipitating uniformly, thus constructing uniformly distributed zinc oxide nanocrystal clusters on the rod surface. The interface between the two forms a strong heterojunction through chemical bonding, which greatly optimizes the separation efficiency of photogenerated electrons and holes, providing a foundation for enhancing photocatalytic antibacterial activity. The final fourth stage, namely the structural solidification and surface engineering stage, involves high-temperature calcination with a dual purpose: firstly, to completely remove residual organic species from the previous steps; and secondly, to further increase the crystallinity of lithium magnesium silicate and zinc oxide, and to further enhance atomic interdiffusion and bonding at the interface, forming a stable composite ceramic phase. After calcination, more highly active silanol groups are exposed on the material surface.In subsequent vapor phase surface modification, hydrophobic silanizing reagent molecules undergo condensation reactions with these silanol groups, grafting low surface energy organic long chains onto the nanomaterial surface in the form of covalent bonds, thereby transforming the hydrophilic surface into a durable hydrophobic surface. This property is crucial to the moisture-proof performance of the final composite material.

[0014] According to a preferred embodiment of the present invention, in step A1, the hydrothermal reaction time at 175-185°C is 24-30 h; the concentration of the lithium hydroxide ethanol solution is 2.4-2.6 mol / L.

[0015] According to a preferred embodiment of the present invention, in step A2, the reaction is continuously stirred for 6-8 hours; the reaction is stirred at 58-62°C for 12-14 hours.

[0016] According to a preferred embodiment of the present invention, in step A3, the maturation time is 6-8 hours.

[0017] According to a preferred embodiment of the present invention, in step A4, the calcination time at 445-455°C is 2-4 hours.

[0018] The beneficial effects of this invention are as follows: The method for preparing food plastic packaging bags and its dedicated inorganic modified material provided by this invention achieve significant breakthroughs in multiple dimensions and synergistic effects, with comprehensive performance far superior to conventional modification schemes for existing bio-based packaging materials. The core technical effect is reflected in the comprehensive leap in functional properties of the prepared composite packaging material. This is primarily attributed to the novel design of magnesium lithium silicate and zinc oxide heterostructure nanorods. This material, with its one-dimensional and multi-dimensional composite core-shell hollow structure, forms an unprecedented synergistic effect with the bacterial cellulose nanofiber network. In terms of mechanical properties, the high aspect ratio nanorods, acting as highly efficient reinforcing agents, are uniformly dispersed in the matrix and bonded to it through strong hydrogen bonds and coordination bonds. This effectively bridges fibers, transfers and disperses stress, thereby achieving a simultaneous and significant improvement in the tensile strength and toughness of the composite film even with extremely low addition amounts, overcoming the embrittlement problem often associated with traditional filler reinforcement. In terms of barrier properties, these highly oriented nanorods construct a dense "nanomania" physical barrier within the film, significantly extending the diffusion paths of water and oxygen molecules. Simultaneously, the surface-modified hydrophobic nanorods significantly reduce the overall surface energy of the composite material, transforming it from hydrophilic to hydrophobic, thus achieving dual and highly efficient barrier against both water vapor and oxygen permeability. Regarding active protection, the zinc oxide nanocrystals in the heterostructure and the trace metal ions loaded within the cavity generate a multi-mode antibacterial synergistic effect, simultaneously exerting contact sterilization, photocatalytic generation of active oxygen for sterilization, and ion-release sterilization. This endows the packaging material with broad-spectrum, robust, and long-lasting antibacterial capabilities and effectively shields against ultraviolet radiation, providing more comprehensive protection for the contents.

[0019] From the perspective of production process and feasibility, the technical solution of this invention has good prospects for industrialization. Although the preparation process of the core heterostructure nanorods involves multiple precisely controlled chemical reactions, including hydrothermal crystallization, template-guided self-assembly, ion exchange, heteroepitaxial growth, and vapor-phase surface modification, ensuring the accuracy of the modified material's structure and the reliability of its function, the final packaging film preparation process is greatly simplified. The film forming adopts mature solution blending, casting coating, and low-temperature hot pressing processes. The entire process uses water as the main solvent, which is mild and easy to control, requires no complex and expensive special equipment, has high compatibility with existing bio-based material processing lines, and is very suitable for large-scale production.

[0020] Ultimately, the technical effects of this invention translate into superior food preservation capabilities and positive environmental benefits at the product level, aligning with the core requirements of sustainable development. Food packaging bags produced by this method, possessing multiple functions including high strength, high barrier properties, hydrophobicity, and antibacterial properties, can effectively inhibit microbial growth, slow down oxidative rancidity, and reduce moisture loss in practical packaging applications for perishable foods such as fresh fruits and vegetables, meats, and pastries. This significantly extends the shelf life of food and enhances food safety and commercial value. Detailed Implementation

[0021] 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.

[0022] Example 1 The preparation steps of lithium magnesium silicate-zinc oxide heterostructure nanorods are as follows: Step A1: Under argon protection, dissolve 100g of magnesium nitrate hexahydrate and 107g of tetraethyl orthosilicate in a mixed solvent of 1000g anhydrous ethanol and 250g deionized water. While stirring with a magnetic stirrer at 500rpm, slowly add a 2.5mol / L lithium hydroxide ethanol solution using a constant-pressure dropping funnel until the pH of the system reaches 10.5, at which point a milky white gel forms. Transfer the entire gel to a 1000mL polytetrafluoroethylene-lined high-pressure reactor and place it in a forced-air drying oven for hydrothermal reaction at 180℃ for 24h. After the reaction, allow the reactor to cool naturally to room temperature. Open the reactor, remove the contents, and collect the precipitate by centrifugation at 8000rpm for 15min. Wash the precipitate three times each with alternating amounts of 800mL anhydrous ethanol and 800mL deionized water. The final washed product was redispersed in 500g of deionized water and placed in an ice-water bath. The mixture was then ultrasonically treated for 1.5h using an ultrasonic cell disruptor at a power of 1000W and a pulse mode (2s operation, 1s interval) to obtain a uniform, semi-transparent lithium magnesium silicate nanosheet colloidal dispersion.

[0023] Step A2: Transfer all the above-mentioned nanosheet colloidal dispersion to a 2000 mL three-necked flask equipped with a reflux condenser. Heat the flask in an oil bath to 85°C and start mechanical stirring at a speed of 300 rpm. Using a micro-syringe pump, inject 0.1 mol / L hexadecyltrimethylammonium bromide aqueous solution into the flask at a rate of 1 mL / min until the final calculated concentration in the reaction system is 5 mmol / L. Maintain this temperature and stirring speed for 7 hours. After the reaction is complete, transfer the reaction solution to a centrifuge bottle and centrifuge at 8000 rpm for 20 min to collect the solid. Repeat the process of washing and centrifuging the obtained solid with 800 mL of deionized water preheated to 70°C five times. Use silver nitrate solution to test the supernatant after the last centrifugation. If no pale yellow silver bromide precipitate is formed, it indicates that CTAB has been washed away. Redisperse the washed and purified nanorods in 500 g of deionized water to obtain a nanorod dispersion. Under light-protected conditions, a silver nitrate solution prepared by dissolving 1.0 g of silver nitrate in 50 g of deionized water was added to the dispersion. The three-necked flask was wrapped with aluminum foil to protect it from light, and the oil bath temperature was maintained at 60°C. The stirring speed was 300 rpm, and the reaction was continued for 12 h. After the reaction was completed, the mixture was centrifuged, and the resulting precipitate was washed three times with deionized water to obtain the initial product of silver-loaded lithium magnesium silicate nanorods.

[0024] Step A3: Redisperse all the initial products in a mixed solvent of 1000g ethylene glycol and 250g dimethyl sulfoxide in a three-necked flask. Under continuous nitrogen purging and heating in a 65°C water bath, stir (500 rpm). Using two constant flow pumps, simultaneously add 150mL of 0.1mol / L zinc acetate in ethylene glycol and 150mL of 0.2mol / L dimethylaminoethanol in dimethyl sulfoxide solution to the suspension, strictly controlling the dropping rate of the two components to ensure simultaneous addition within 3 hours. After the addition is complete, raise the water bath temperature to 85°C and continue stirring for 6 hours. After the reaction is complete, cool the reaction solution to room temperature and collect the solid by centrifugation. Wash the solid three times, successively with 200mL of N,N-dimethylformamide and 200mL of anhydrous ethanol, to obtain the washed solid.

[0025] Step A4: Transfer the washed solid to a corundum crucible and place it in the center of a tube furnace. Under air atmosphere, heat to 450℃ at a rate of 2℃ / min and calcine at this temperature for 2 hours. After calcination, turn off the heating power and allow the tube furnace to cool naturally to below 185℃. Open the furnace tube and quickly transfer the crucible to a glove box filled with high-purity nitrogen to cool to room temperature, obtaining the cooled powder. Weigh 100g of this cooled powder and place it in a vacuum desiccator. Place a small beaker containing 1.5g of hexamethyldisilazane liquid at the bottom of the desiccator. After sealing the desiccator, place the entire assembly in a 75℃ forced-air drying oven for 22 hours. After treatment, remove the powder and dry it in an 80℃ vacuum drying oven for 6 hours to obtain lithium magnesium silicate-zinc oxide heterostructure nanorods.

[0026] The preparation steps for food plastic packaging bags are as follows: Step S1: Weigh 100g of commercially available bacterial cellulose wet membrane (water content approximately 98%), rinse with plenty of deionized water until the filtrate is neutral, and obtain the washed bacterial cellulose membrane. Add it together with 9900g of deionized water into the feed cup of a high-speed tissue homogenizer, and homogenize at 10000rpm for 7min to obtain a uniform bacterial cellulose nanofiber suspension.

[0027] Step S2: Accurately weigh 3.0 g of the prepared lithium magnesium silicate-zinc oxide heterostructure nanorods and place them in a beaker. Add 75 g of anhydrous ethanol. Place the beaker in an ultrasonic cleaner and ultrasonically disperse the nanorods at 40 kHz and 300 W for 30 min to obtain a stable nanorod suspension. While continuously stirring all the bacterial cellulose suspension obtained in step S1 at a mechanical stirrer at a rate of 500 rpm, slowly pour the nanorod suspension into the mixture. After the addition is complete, continue stirring at this rate for a total of 3 h to obtain a uniformly mixed slurry.

[0028] Step S3: Transfer the blended slurry to a vacuum degassing machine and degas for 15 minutes at a vacuum of -0.095 MPa. Using an automatic film casting machine, cast the degassed slurry onto a flat polyethylene terephthalate substrate, setting the wet film thickness to 0.8 mm to obtain a coated substrate. Move the substrate horizontally into a forced-air drying oven, first drying at 40°C for 13 hours, then increasing the temperature to 60°C and continuing drying for 6 hours. After the film is completely dry and automatically peels off from the substrate, remove the self-supporting dried film.

[0029] Step S4: Cut the dried film to an appropriate size and place it between two PTFE templates of the flat vulcanizing machine. Set the hot-pressing temperature to 80℃, the pressure to 5MPa, and the hot-pressing time to 3 minutes. After the hot-pressing process is completed, remove the film, cut it, and roll it up to obtain the final food plastic packaging bag.

[0030] Example 2 The specific implementation method is the same as in Example 1, except that the preparation steps of the magnesium lithium silicate-zinc oxide heterostructure nanorods are as follows: Step A1: Under argon protection, 80g of magnesium nitrate hexahydrate and 104g of tetraethyl orthosilicate were dissolved in a mixed solvent of 800g anhydrous ethanol and 200g deionized water. A 2.5mol / L lithium hydroxide ethanol solution was added dropwise while stirring at 500rpm until the pH reached 10.4, yielding a gel. The gel was transferred to a high-pressure reactor and hydrothermally reacted at 175℃ for 30h. After cooling, the precipitate was collected by centrifugation and washed three times alternately with ethanol and water. The product was dispersed in 400g of deionized water and sonicated at 1000W (pulse mode) in an ice-water bath for 1.5h to obtain a nanosheet colloidal dispersion.

[0031] Step A2: Transfer the dispersion to a three-necked flask, heat to 84°C, and stir at 300 rpm. Add 0.1 mol / L CTAB aqueous solution dropwise until the final concentration of the system is 4 mmol / L, and react for 6 h. Collect the solid by centrifugation and wash repeatedly with 70°C hot water until no bromide ions are detected. Disperse the purified nanorods in 400 g of deionized water, add silver nitrate solution containing 0.8 g of silver ions under light protection, and react at 58°C for 14 h. After centrifugation, wash three times with water to obtain the silver-loaded primary product.

[0032] Step A3: The initial product was dispersed in a mixed solvent of 720 g ethylene glycol and 180 g dimethyl sulfoxide. Under nitrogen protection and in a 64°C water bath, the mixture was stirred at 500 rpm while simultaneously adding 120 mL of 0.1 mol / L zinc acetate ethylene glycol solution and 120 mL of 0.2 mol / L dimethylaminoethanol DMSO solution over 3 hours. The mixture was then heated to 84°C and allowed to mature for 8 hours. After the reaction, the solid was centrifuged and washed three times each with DMF and anhydrous ethanol.

[0033] Step A4: The solid was heated to 445℃ at a rate of 1℃ / min and calcined for 4 hours. After natural cooling to 180℃, it was transferred to a nitrogen glove box for cooling. 100g of powder was placed together with 1.0g of hexamethyldisilazane liquid in a vacuum desiccator and treated in a 70℃ oven for 24 hours. Finally, it was vacuum dried at 80℃ for 6 hours to obtain nanorods.

[0034] The preparation steps for food plastic packaging bags are as follows: Step S1: Take 80g of bacterial cellulose wet film, wash it, mix it with 9800g of deionized water, and homogenize it at 10000rpm for 5min to obtain a suspension.

[0035] Step S2: Weigh 1.5g of the above nanorods and disperse them in 50g of anhydrous ethanol, then sonicate for 30min. Add all of the bacterial cellulose suspension while stirring, and continue stirring at 500rpm for 2h to obtain a blended slurry.

[0036] In step S3, after vacuum degassing the slurry for 15 minutes, it is cast onto the substrate (wet film thickness 0.8 mm). It is first dried at 38°C for 14 hours, and then dried at 58°C until the film peels off.

[0037] Step S4: The dried film is hot-pressed at 78°C and 5MPa for 4 minutes, then cut and rolled to obtain the finished product. Example

[0038] The specific implementation method is the same as in Example 1, except that the preparation steps of the magnesium lithium silicate-zinc oxide heterostructure nanorods are as follows: Step A1: Under argon protection, 120g of magnesium nitrate hexahydrate and 110g of tetraethyl orthosilicate were dissolved in a mixed solvent of 1200g anhydrous ethanol and 300g deionized water. A 2.5mol / L lithium hydroxide ethanol solution was added dropwise while stirring at 500rpm until the pH reached 10.6, yielding a gel. The gel was transferred to a high-pressure reactor and hydrothermally reacted at 185℃ for 24h. After cooling, the precipitate was collected by centrifugation and washed three times alternately with ethanol and water. The product was dispersed in 600g of deionized water and sonicated at 1000W (pulse mode) in an ice-water bath for 1.5h to obtain a nanosheet colloidal dispersion.

[0039] Step A2: Transfer the dispersion to a three-necked flask, heat to 86°C, and stir at 300 rpm. Add 0.1 mol / L CTAB aqueous solution dropwise until the final concentration of the system is 6 mmol / L, and react for 8 h. Collect the solid by centrifugation and wash repeatedly with 75°C hot water until no bromide ions are detected. Disperse the purified nanorods in 600 g of deionized water, add silver nitrate solution containing 1.2 g of silver ions under light protection, and react at 62°C for 12 h. After centrifugation, wash three times with water to obtain the silver-loaded primary product.

[0040] Step A3: The initial product was dispersed in a mixed solvent of 1250 g ethylene glycol and 250 g dimethyl sulfoxide. Under nitrogen protection and in a 66°C water bath, the mixture was stirred at 500 rpm while simultaneously adding 180 mL of 0.1 mol / L zinc acetate ethylene glycol solution and 180 mL of 0.2 mol / L dimethylaminoethanol DMSO solution over 3 hours. The mixture was then heated to 86°C and allowed to mature for 6 hours. After the reaction, the solid was centrifuged and washed three times each with DMF and anhydrous ethanol.

[0041] Step A4: The solid was heated to 455℃ at a rate of 3℃ / min and calcined for 2 hours. After natural cooling to 190℃, it was transferred to a nitrogen glove box for cooling. 100g of powder was placed together with 3.0g of hexamethyldisilazane liquid in a vacuum desiccator and treated in an oven at 80℃ for 20 hours. Finally, it was vacuum dried at 80℃ for 6 hours to obtain nanorods.

[0042] The preparation steps for food plastic packaging bags are as follows: Step S1: Take 120g of bacterial cellulose wet film, wash it, mix it with 9900g of deionized water, and homogenize it at 10000rpm for 10min to obtain a suspension.

[0043] Step S2: Weigh 5.0 g of the above nanorods and disperse them in 100 g of anhydrous ethanol, then sonicate for 30 min. Add all of the bacterial cellulose suspension while stirring, and continue stirring at 500 rpm for 4 h to obtain a blended slurry.

[0044] In step S3, after vacuum degassing the slurry for 15 minutes, it is cast onto the substrate (wet film thickness 0.8 mm). It is first dried at 42°C for 12 hours, and then dried at 62°C until the film peels off.

[0045] Step S4: The dried film is hot-pressed at 82°C and 5MPa for 2 minutes, then cut and rolled to obtain the finished product.

[0046] Comparative Example 1 The specific implementation method is the same as in Example 1, except that this comparative example provides a pure bacterial cellulose membrane as a control. The preparation steps of the food plastic packaging bag are as follows: Step S1, take 100g of bacterial cellulose wet membrane, wash it, mix it with 9900g of deionized water, and homogenize it at 10000rpm for 7min to obtain a suspension. Step S3, after vacuum degassing the suspension for 15min, cast it onto a substrate (wet membrane thickness 0.8mm). First dry at 40℃ for 13h, then dry at 60℃ until the membrane peels off. Step S4, hot press the dried film at 80℃ and 5MPa for 3min, cut and roll it to obtain a pure bacterial cellulose membrane. This comparative example does not include step S2, that is, it does not add lithium magnesium silicate-zinc oxide heterostructure nanorods.

[0047] Comparative Example 2 The specific implementation method is the same as in Example 1, except that this comparative example uses a physically mixed ordinary inorganic filler. First, the physically mixed filler is prepared: 1.5g of lithium magnesium silicate micron powder calcined at 450℃ for 2h, 1.5g of ordinary zinc oxide nanopowder, and 0.015g of nano silver carbonate powder are weighed and added to 100g of anhydrous ethanol, and sonicated for 30min to obtain a suspension. The preparation steps of the food plastic packaging bag are as follows: Step S1 is the same as in Example 1. Step S2: The above filler suspension is added to all the bacterial cellulose suspension under stirring, and stirred at 500rpm for 3h. Subsequent steps S3 and S4 are exactly the same as in Example 1.

[0048] Comparative Example 3 The specific implementation method is the same as in Example 1, except that hydrophobic lithium magnesium silicate nanorods without silver loading and zinc oxide growth are prepared in this comparative example. The preparation steps are as follows: Step A1 is the same as in Example 1. The first half of Step A2 is the same as in Example 1, that is, CTAB is added and reacted at 85°C for 7 hours, centrifuged and thoroughly washed with 70°C hot water to obtain pure lithium magnesium silicate nanorods. Then, Step A4 is directly performed: the nanorods are heated to 450°C at 2°C / min and calcined for 2 hours, then cooled naturally and transferred to a glove box for cooling. 100g of cooled powder is taken and treated with 1.5g of hexamethyldisilazane in a vacuum desiccator at 75°C for 22 hours, and then vacuum dried at 80°C for 6 hours to obtain hydrophobic lithium magnesium silicate nanorods. The preparation steps of the food plastic packaging bag are as follows: Step S1 is the same as in Example 1. Step S2, 3.0g of the above hydrophobic nanorods are weighed, dispersed in 75g of anhydrous ethanol, sonicated and then mixed with all bacterial cellulose suspension for 3 hours. Subsequent steps S3 and S4 are exactly the same as in Example 1.

[0049] Performance testing According to relevant national and industry standards, the food plastic packaging bags prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to the following methods, which included the following steps: The properties of the films prepared in the embodiments and comparative examples of this invention were tested under the following conditions: the samples were conditioned in a standard environment at 23°C and 50% relative humidity for at least 48 hours before all tests were performed. Tensile strength and elongation at break were tested using a universal testing machine. The films were cut into strips with a width of 15 mm and a gauge length of 50 mm, and subjected to uniaxial stretching at a constant stretching rate of 50 mm / min until the sample broke. The maximum load and the length change at break were recorded, and the tensile strength (MPa) and elongation at break (%) were calculated respectively.

[0050] The water vapor transmission rate was tested using the permeation cup method. The membrane was sealed in a permeation cup containing 3 / 4 cup of dry anhydrous calcium chloride. The cup was placed in a constant temperature and humidity chamber at 38°C and 90% relative humidity. The total mass of the permeation cup was accurately weighed every hour, and the measurement was continued for more than 24 hours. The water vapor transmission rate was calculated based on the increase in mass per unit time, membrane thickness, and area. The unit is expressed as g·mm / (m²·day·kPa).

[0051] The oxygen permeability test uses a differential pressure gas permeation apparatus. The membrane is cut into a circular sample with a diameter of 100 mm and installed in the test chamber. At 23°C, one side of the membrane is filled with pure oxygen (1 atm) while the other side is evacuated. The volume of oxygen permeating through the membrane per unit time after stabilization is measured. The oxygen permeability is calculated by combining the membrane thickness and the unit is expressed as cm³·mm / (m²·day·atm).

[0052] The ultraviolet shielding rate was tested using a UV-Vis spectrophotometer. The film was cut into a rectangle suitable for the size of the sample cell, and its transmittance was measured directly at a wavelength of 380 nm. The ultraviolet shielding rate was calculated using the formula (1 - transmittance) x 100%.

[0053] The antibacterial rate test was conducted using the film covering method. The film sample was cut into 50mm x 50mm squares, sterilized by ultraviolet light, and then covered with an inoculum containing a concentration of 1x10⁻⁶. 5 After incubating CFU / mL Escherichia coli culture on nutrient agar plates at 37°C for 24 hours, the number of colonies in the film-covered area was counted and compared with the control area without film to calculate the antibacterial rate.

[0054] The water contact angle test was performed using a contact angle measuring instrument. The film was flattened and fixed on the sample stage. The droplet method was used, and 5 μL of deionized water was dropped onto the film surface using a microsyringe. The droplet profile image was analyzed by the instrument software, and the static contact angle (°) was read directly.

[0055] Test results: Table 1: Test results of each embodiment and comparative example

[0056] As can be seen from Table 1, Examples 1-3 successfully and synergistically solved the technical problem that existing bio-based food packaging materials are difficult to simultaneously possess high barrier properties, strong antibacterial properties, and high mechanical strength, and that the comprehensive modification process is complex, by introducing the magnesium lithium-zinc oxide heterostructure nanorods designed in this invention.

[0057] Specifically, the performance data of the pure bacterial cellulose membrane in Comparative Example 1 revealed the inherent limitations of the basic material in terms of barrier properties (water vapor permeability 12.8 g·mm / (m²·day·kPa), oxygen permeability 15.3 cm³·mm / (m²·day·atm)), antibacterial properties (inactive), and mechanical strength (tensile strength 118 MPa), clarifying the current situation that a single biopolymer cannot meet the requirements of high-performance packaging.

[0058] Comparative Example 2 used a simple physical mixture of commercially available inorganic powders. The results showed that although this method could bring certain antibacterial properties (antibacterial rate 99.3%) and UV shielding (about 68%), the improvement in mechanical properties was very limited (tensile strength 140 MPa, and elongation at break decreased to 5.8%, indicating increased material brittleness). Furthermore, the improvement in water vapor and oxygen barrier properties (water vapor permeability 9.5 g·mm / (m²·day·kPa), oxygen permeability 11.8 cm³·mm / (m²·day·atm)) was far from ideal. This proves that the dispersion and interfacial bonding problems of unstructured fillers limit their reinforcement efficiency and prevent functional integration.

[0059] Comparative Example 3 used only hydrophobically treated lithium magnesium silicate nanorods. The data showed that this approach could effectively improve the mechanical properties (tensile strength 168 MPa) and hydrophobicity (contact angle 102°) of the material. It also improved the barrier properties to some extent by means of the physical barrier effect of the nanorods (water vapor transmission rate 6.8 g·mm / (m²·day·kPa), oxygen transmission rate 8.5 cm³·mm / (m²·day·atm)). However, it did not have effective antibacterial properties (antibacterial rate only 30.5%) or ultraviolet shielding ability (about 25%). This clearly confirms that without active functional components (silver, zinc oxide) and heterogeneous structure, the material cannot be endowed with active protective properties.

[0060] In contrast, the embodiments of the present invention, especially Embodiment 1, demonstrate a comprehensive leap in performance: the tensile strength reaches 210 MPa, and the elongation at break remains at 15.0%, achieving simultaneous optimization of strength and toughness; the water vapor transmission rate and oxygen transmission rate are significantly reduced to 3.3 g·mm / (m²·day·kPa) and 4.6 cm³·mm / (m²·day·atm), respectively, showing excellent barrier performance; at the same time, the antibacterial rate exceeds 99.99%, the ultraviolet shielding rate exceeds 99%, and the contact angle is as high as 106°, proving its powerful active antibacterial, ultraviolet shielding, and hydrophobic properties.

[0061] This series of data collectively demonstrates that the structured, multifunctional integrated nanomodifier prepared by the present invention through precise chemical design can produce a strong interfacial bond and synergistic effect with the bacterial cellulose matrix in a simple solution blending-casting process with a low addition amount. This overcomes the core pain points of traditional modification methods, such as the inability to balance performance, low filler efficiency, and cumbersome processes, thus providing an innovative solution with both excellent comprehensive performance and good processing feasibility.

[0062] 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 method for preparing a food plastic packaging bag, characterized in that, Includes the following steps: S1, by weight, 80-120 parts of bacterial cellulose membrane are washed with deionized water until neutral to obtain washed bacterial cellulose membrane. The washed bacterial cellulose membrane is mixed with 9800-9900 parts of deionized water and placed in a homogenizer for homogenization to obtain bacterial cellulose nanofiber suspension. S2, 1.5-5.0 parts of magnesium lithium silicate-zinc oxide heterostructured nanorods are dispersed in 50-100 parts of anhydrous ethanol and ultrasonically treated to obtain a suspension; the suspension is added to the bacterial cellulose nanofiber suspension under stirring and stirring is continued to obtain a blended slurry; S3, the blended slurry is subjected to vacuum degassing treatment, and the slurry is cast onto a polyethylene terephthalate substrate to obtain a coated substrate; the coated substrate is transferred to a drying oven and dried at 38-42℃, and then dried at 58-62℃ to obtain a dried film; S4. Place the dried film in a flat vulcanizing machine and hot-press it at 78-82℃. After hot pressing, cut and roll it up.

2. The method for preparing food plastic packaging bags according to claim 1, characterized in that, In step S1, the homogenization process takes 5-10 minutes.

3. The method for preparing food plastic packaging bags according to claim 1, characterized in that, In step S2, the stirring time continues for 2-4 hours.

4. The method for preparing food plastic packaging bags according to claim 1, characterized in that, In step S3, the drying time at 38-42℃ is 12-14 hours.

5. The method for preparing food plastic packaging bags according to claim 1, characterized in that, In step S4, the hot pressing treatment at 78-82℃ takes 2-4 minutes.

6. The method for preparing food plastic packaging bags according to any one of claims 1-5, characterized in that, The preparation steps of the lithium magnesium silicate-zinc oxide heterostructure nanorods include: A1, by weight, under argon protection, 80-120 parts of magnesium nitrate hexahydrate and 104-110 parts of tetraethyl orthosilicate were dissolved in a mixed solvent of 800-1200 parts of anhydrous ethanol and 200-300 parts of deionized water. While stirring, an ethanol solution of lithium hydroxide was added dropwise to adjust the pH to 10.4-10.6, resulting in a gel. The gel was transferred to a high-pressure reactor and subjected to hydrothermal reaction at 175-185℃. After the reaction, the mixture was naturally cooled to room temperature, and the precipitate was collected by centrifugation. The precipitate was washed alternately with ethanol and deionized water to obtain the product. The product was redispersed in deionized water and ultrasonically treated in an ice-water bath to obtain a colloidal dispersion of lithium magnesium silicate nanosheets. A2. The colloidal dispersion of lithium magnesium silicate nanosheets was transferred to a three-necked flask, heated to 84-86℃ and stirred. Hexadecyltrimethylammonium bromide aqueous solution was added, and the reaction was continued with stirring. The nanorods were collected by centrifugation and washed with deionized water at 60-80℃ to obtain washed nanorods. The washed nanorods were redispersed in deionized water, and silver nitrate solution was added under light-protected conditions. The reaction was stirred at 58-62℃. After the reaction was completed, the precipitate was separated by centrifugation and washed with deionized water to obtain the silver-loaded lithium magnesium silicate nanorod primary product. A3. The silver-loaded lithium magnesium silicate nanorods were redispersed in a mixed solvent of ethylene glycol and dimethyl sulfoxide to obtain a suspension. Under nitrogen protection and heating in a water bath at 64-66°C, a zinc acetate ethylene glycol solution and a dimethyl aminoethanol dimethyl sulfoxide solution were added dropwise to the suspension. After the addition was complete, the temperature was raised to 84-86°C for further aging. After the reaction was completed, the solid was collected by centrifugation and washed with N,N-dimethylformamide and anhydrous ethanol to obtain the washed solid. A4. The washed solid is placed in a tube furnace and calcined at 445-455℃ in an air atmosphere. After calcination, it is naturally cooled to 180-190℃ to obtain powder. The powder is transferred to a glove box filled with nitrogen and cooled to room temperature to obtain cooled powder. The cooled powder is placed in a vacuum dryer and hexamethyldisilazane vapor is introduced. The vacuum dryer is placed in an oven at 70-80℃ for treatment. After treatment, it is dried in a vacuum drying oven at 78-82℃.

7. The method for preparing food plastic packaging bags according to claim 6, characterized in that, In step A1, the hydrothermal reaction at 175-185℃ takes 24-30 hours; the concentration of the lithium hydroxide ethanol solution is 2.4-2.6 mol / L.

8. The method for preparing food plastic packaging bags according to claim 6, characterized in that, In step A2, the reaction is continuously stirred for 6-8 hours; the reaction is stirred at 58-62℃ for 12-14 hours.

9. The method for preparing a food plastic packaging bag according to claim 6, characterized in that, In step A3, the maturation time continues for 6-8 hours.

10. The method for preparing a food plastic packaging bag according to claim 6, characterized in that, In step A4, the calcination time at 445-455℃ is 2-4 hours.

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