Biodegradable film packaging material and preparation method thereof

Abstract

The invention provides a biodegradable film packaging material and a preparation method thereof.The preparation method comprises the steps that a natural reducing agent and an oxidation precursor solution are mixed, the pH of the mixed solution is adjusted to be alkaline, centrifugation is conducted after heating and stirring, precipitates are calcined, and filling particles are obtained; mixing the hard-phase material and the soft-phase material, adding a functional additive, carrying out melt extrusion molding to obtain master batches, and carrying out hot press molding on the master batches to obtain a bottom layer film; mixing the filling particles with a dispersing solvent to obtain filling sol, coating the surface of the bottom layer film with the filling sol to form a barrier layer, and sequentially coating the barrier layer with a color developing film and a waterproof coating film to obtain the biodegradable film packaging material. The filling particles serve as hard nodes, the puncture resistance and tensile modulus of the bottom layer film are remarkably improved, the requirements for blocking and breaking resistance in the packaging process are met, and damage prompting is achieved through the developing film.

Description

Technical Field

[0001] This invention belongs to the field of packaging materials technology, and in particular relates to a biodegradable film packaging material and its preparation method. Background Technology

[0002] Biodegradable film materials refer to sheet-like or film-like products made from natural polymers, compostable bio-based polyesters, or a blend of both. When placed in environments containing microorganisms, such as soil, compost, or the ocean, the polymer chains can be enzymatically and hydrolyzed, ultimately transforming into carbon dioxide, water, and biomass, leaving no recalcitrant microplastic residue. Compared to traditional petrochemical plastic films, they are not only renewable in origin and have low carbon emission coefficients, but also can be incorporated into industrial composting systems along with kitchen waste or garden waste after use, achieving a closed-loop recycling system.

[0003] Traditional biodegradable packaging films are mostly based on single aliphatic polyesters (such as polylactic acid and polycaprolactone) or natural polysaccharide modified systems. These materials are inherently highly polar, have weak inter-segment hydrogen bonds, and limited crystallinity, resulting in large free volume channels between molecules that allow easy penetration by gases and water vapor. Furthermore, these materials lack toughness and resistance to microcrack propagation, making them easily punctured or broken by logistical impacts. Without high-modulus inorganic phase filling and interfacial compatibility design, it is difficult to balance mechanical strength and barrier properties, often resulting in both air leakage and easy breakage in cold chain or express delivery scenarios. On the other hand, traditional films are often considered passive barriers; damage relies on visual inspection to find cracks, and spoilage on smell or laboratory testing, leaving users unaware that the packaging has ruptured. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a biodegradable film packaging material and its preparation method, which aims to solve the problem that the biodegradable film packaging material has insufficient toughness and cannot indicate damage.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows: 1. A method for preparing a biodegradable film packaging material, characterized in that the steps include: S1. Mix the natural reducing agent and the oxidation precursor solution, adjust the pH of the mixed solution to alkaline, heat and stir, centrifuge, and calcine the precipitate to obtain the filled particles; S2. Mix the hard phase material and the soft phase material, add functional additives, and then melt extrude to obtain a masterbatch. Hot press the masterbatch to obtain the bottom film. S3. Mix the filler particles with the dispersion solvent to obtain a filler sol. Coat the filler sol onto the surface of the bottom film to form a barrier layer. Coat the barrier layer with a color developing film and a waterproof coating film in sequence to obtain a biodegradable film packaging material.

[0006] In some embodiments, step S1 includes: S1.1 Mix natural plant powder with deionized water, heat to 80℃ and stir for 60 minutes, then hot filter to obtain natural reducing agent. Adjust the pH of natural reducing agent to neutral. S1.2 Add a reducing agent to the metal source solution to obtain an oxidation precursor solution. Simultaneously add the oxidation precursor solution and an alkaline solution to the natural reducing agent and maintain the temperature at 80~90℃. S1.3 Detect the redox potential and pH value of the mixed solution. When the redox potential reaches the preset range, stop adding the oxidation precursor solution. When the pH value of the mixed solution reaches 10.0±0.1, stop adding the alkaline solution and obtain the reaction slurry. S1.4 Centrifuge the reaction slurry at 7000g for 10 minutes, discard the supernatant, resuspend it in a mixture of water and ethanol and sonicate for 2-3 minutes. Repeat the washing process 3 times to obtain a wet precipitate. S1.5. Mix the template agent in the wet precipitate, freeze-dry to obtain a sheet, heat the sheet to 300℃ at 2℃ / min in air atmosphere, hold for 1h, then heat to 380℃ and hold for 30min to obtain sintered powder. S1.6. The sintered powder is ball-milled for 5-10 minutes, sonicated for 10 minutes, heated to 60℃ and vacuum dried to obtain the filling particles.

[0007] In some embodiments, in step S1, the natural plant powder includes at least one of fig powder, pomegranate peel powder, green tea powder, and grape seed powder; the metal source solution includes at least one of zinc source, iron source, titanium source, magnesium source, manganese source, silver source, and bismuth source; the zinc source includes at least one of zinc nitrate hexahydrate, zinc acetate dihydrate, zinc sulfate heptahydrate, zinc chloride, and zinc acetylacetonate; the iron source includes at least one of ferric nitrate nonahydrate, ferric chloride hexahydrate, ferrous sulfate heptahydrate, ferric citrate, and ferric acetylacetonate; and the titanium source includes tetraisopropoxy titanium, tetrabutoxy titanium, tetraethoxy titanium, titanium tetrachloride, and ammonium titanium oxalate. At least one of the following: magnesium source includes at least one of magnesium nitrate hexahydrate, magnesium sulfate heptahydrate, magnesium acetate tetrahydrate, magnesium chloride hexahydrate, and magnesium oxalate dihydrate; manganese source includes at least one of manganese nitrate tetrahydrate, manganese chloride tetrahydrate, manganese acetate tetrahydrate, manganese sulfate monohydrate, and potassium permanganate; silver source includes at least one of silver nitrate, silver acetate, silver perchlorate, silver trifluoroacetate, and diamine silver complex; bismuth source includes at least one of bismuth nitrate pentahydrate, bismuth chloride, bismuth acetate, bismuth subnitrate, basic bismuth nitrate, and bismuth citrate; and template agent includes at least one of pullulan, sodium alginate, and gum arabic.

[0008] In some embodiments, step S2 includes: S2.1 The functional additives include compatibilizers, epoxy chain extenders and bio-based antioxidants. First, the flexible phase material and compatibilizer are mixed, and then the hard phase material, epoxy chain extender and bio-based antioxidant are added. The mixture is heated to 80°C and dried for 2 hours to obtain the mixed filler. S2.2 Place the mixed filler in a twin-screw extruder, set the temperatures of each zone of the barrel to 200℃, 195℃, 190℃, 185℃, 180℃, 175℃, and 170℃ respectively, set the die head temperature to 175℃, set the screw speed to 180~240rpm, set the vacuum pressure to -0.08MPa, extrude and water-cooled pellets, then pass through 80℃ hot air for 20min, and transfer to a drying oven at 50℃ for 2h to obtain masterbatch; S2.3, The masterbatch is melt-extruded and cast to obtain a low-layer film of a predetermined thickness [2]; S2.4. Stretch the bottom film unidirectionally by 1.8 to 2.2 times at a stretching table at 70 to 80°C, then heat it to 110°C and hold for 10 minutes for annealing.

[0009] In some embodiments, in step S2, the compatibilizer includes at least one of ethylene-butyl acrylate-glycidyl methacrylate, ethylene-methacrylate-glycidyl methacrylate, and epoxidized soybean oil; the epoxy chain extender includes at least one of bisphenol A epoxy resin, Joncryl ADR-4400, Joncryl ADR-4440, and Joncryl ADR-4368; the bio-based antioxidant includes at least one of vitamin E, vitamin C, ferulic acid, and ferulic acid palmitate; the flexible phase material includes at least one of butylene terephthalate-butylene adipate copolymer, butylene succinate-butylene heptaate copolymer, polycaprolactone, and medium- and long-chain polyhydroxyalkanoates; and the hard phase material includes at least one of polylactic acid, polyglycolic acid, and poly(3-hydroxybutyrate-3-hydroxyvalerate).

[0010] In some embodiments, step S3 includes: S3.1 Add the filler particles to the dispersion solvent, adjust the rotation speed to 8000~10000rpm, rotate for 5~10min, add the binder and then perform ultrasonic dispersion, ultrasonic power of 200~400W, ultrasonic for 10~20min to obtain the filler sol, adjust the pH of the filler sol to 4.5~5.0, and adjust the viscosity of the filler sol at 25℃ to 60~150mPa·s; S3.2. Apply the filler sol to the bottom film and then blow it with 60℃ hot air for 3~5 minutes to form a barrier layer; S3.3 Dissolve red cabbage anthocyanin powder in an acidic solution to obtain anthocyanin solution. Mix pullulan, gum arabic, and glycerin in deionized water, heat to 50°C and stir for 20 minutes to obtain wall material solution. Mix the anthocyanin solution and wall material solution, adjust the rotation speed to 8000 rpm for pre-emulsification for 3 minutes, and then sonicate with 200W ultrasonic power for 2 minutes to obtain emulsion. S3.4 The emulsion is fed into the spray drying tower at a rate of 6 mL / min using a peristaltic pump. The inlet temperature of the tower is set at 160℃, and the outlet temperature is set at 80℃. Atomization is achieved using a 0.7 mm dual-fluid nozzle, compressed air at 0.25 MPa, and hot air flow rate at 0.35 m³ / min. 3 / min, to obtain spherical microcapsule powder, mix the spherical microcapsule powder with citric acid solution, adjust the rotation speed to 8000 rpm for pre-emulsification for 3 min, and then sonicate with 200W ultrasonic power for 2 min to obtain colorimetric film solution; S3.5. Coat the color developing film solution onto the barrier layer, heat to 50℃ and hold for 5 minutes, then coat with the waterproof coating film solution, heat to 80℃ and dry for 10~20 minutes to obtain the biodegradable film packaging material.

[0011] In some embodiments, in step S3, the dispersing solvent includes at least one of polyvinylpyrrolidone, ammonia, sodium dodecyl sulfate, and polyvinyl alcohol; the acidic solution includes at least one of citric acid-sodium citrate buffer, lactic acid solution, and glacial acetic acid dilution; and the waterproof coating film solution includes at least one of beeswax-carnauba wax composite emulsion, shellac ethanol solution, and polycaprolactone ethyl acetate solution.

[0012] This invention proposes a biodegradable film packaging material, which is prepared by the method described above for preparing a biodegradable film packaging material.

[0013] The method for preparing a biodegradable film packaging material in this invention has the following advantages compared with the prior art: S1 is prepared by green reduction calcination to obtain filler particles, which form a dense barrier layer in S3. Gases and water vapors must take a tortuous path to penetrate. At the same time, the filler particles act as hard nodes, significantly improving the puncture resistance and tensile modulus of the bottom film made by S2. The puncture strength and heat resistance sealing window are improved simultaneously, meeting the needs of cold chain and express delivery for packaging that is both barrier and shock-resistant. S3 has a color-developing film containing anthocyanins printed on the barrier layer. When the film is punctured by external force or the internal pH rises to about 5.5 due to microbial metabolism, the anthocyanins turn from purple to green, which is visible to the naked eye within minutes. The waterproof coating film blocks water but allows volatile acids and alkalis to pass through, ensuring sensitive warning and not being affected by external humidity. In this way, users can judge the freshness of the contents and the integrity of the packaging without opening the package. Attached Figure Description

[0014] Figure 1 This is a schematic flowchart of a method for preparing a biodegradable film packaging material according to one embodiment of the present invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0016] Please refer to Figure 1 This invention proposes a method for preparing a biodegradable film packaging material, the steps of which include: S1. Mix the natural reducing agent and the oxidation precursor solution, adjust the pH of the mixed solution to alkaline, heat and stir, centrifuge, and calcine the precipitate to obtain the filled particles.

[0017] Step S1 includes: S1.1 Mix natural plant powder with deionized water, heat to 80℃ and stir for 60 minutes, then hot filter to obtain a natural reducing agent. Adjust the pH of the natural reducing agent to neutral. The natural plant powder includes at least one of fig powder, pomegranate peel powder, green tea powder, and grape seed powder. The recommended ratio of natural plant powder to water is 1:20 (mass:volume, g:mL). Take 50g of fig powder, add 1000mL of deionized water, heat at 80℃ for 60 minutes, and then filter the residue. Adjust the pH of the resulting extract dropwise with 1mol / L NaOH or dilute ammonia to ≈7. This ensures a stable polyphenol concentration of 0.5~1.0g / L, guaranteeing reducing power while avoiding flocculation caused by sudden changes in strong alkali.

[0018] By extracting plant powders such as fig powder, pomegranate peel powder, green tea powder, or grape seed powder in an 80℃ water bath, the maximum extraction of natural reducing components containing hydroxyl or carboxyl groups, such as polyphenols, flavonoids, and soluble sugars, can be achieved. These active substances, under alkaline and heated conditions, can not only donate electrons to metal ions but also act as soft templates adsorbed onto the crystal nucleus surface during subsequent nucleation, inhibiting excessive crystal growth. Furthermore, the extract is hot-filtered to remove plant residue before being adjusted to neutral pH, avoiding interference from residual strong acids (or bases) on the subsequent reduction-coordination reaction rate and ensuring accurate pH control in the later stages.

[0019] S1.2 A reducing agent is added to the metal source solution to obtain an oxidation precursor solution. The oxidation precursor solution and an alkaline solution are simultaneously added to the natural reducing agent, maintaining the temperature at 80-90℃. The metal source solution includes at least one of zinc, iron, titanium, magnesium, manganese, silver, and bismuth sources. The zinc source includes at least one of zinc nitrate hexahydrate, zinc acetate dihydrate, zinc sulfate heptahydrate, zinc chloride, and zinc acetylacetonate. The iron source includes at least one of ferric nitrate nonahydrate, ferric chloride hexahydrate, ferrous sulfate heptahydrate, ferric citrate, and ferric acetylacetonate. The titanium source includes tetraisopropoxytitanium and tetrabutylene oxide. The source includes at least one of titanium oxyoxygenate, titanium tetraethoxygenate, titanium tetrachloride, and titanium oxalate ammonium; the magnesium source includes at least one of magnesium nitrate hexahydrate, magnesium sulfate heptahydrate, magnesium acetate tetrahydrate, magnesium chloride hexahydrate, and magnesium oxalate dihydrate; the manganese source includes at least one of manganese nitrate tetrahydrate, manganese chloride tetrahydrate, manganese acetate tetrahydrate, manganese sulfate monohydrate, and potassium permanganate; the silver source includes at least one of silver nitrate, silver acetate, silver perchlorate, silver trifluoroacetate, and diamine silver complex; and the bismuth source includes at least one of bismuth nitrate pentahydrate, bismuth chloride, bismuth acetate, bismuth subnitrate, basic bismuth nitrate, and bismuth citrate.

[0020] If zinc nitrate hexahydrate is used, prepare 950 mL of a 0.10 mol / L solution. The reducing agent (such as 0.02 mol / L ascorbic acid) only needs to be added at 0.5–1.0 mol% of the total metal ion moles (9.5–19 mmol in this example, corresponding to 25–50 mL of solution). For alkalinity adjustment, use 1 mol / L NaOH, adding approximately 8–10 mL per liter of the mixture to slowly raise the system to pH 10. The final solid-liquid ratio should be maintained at approximately 1 g metal salt: 100 mL solvent, balancing nucleation rate and viscosity control.

[0021] After preparing a stable solution of a metal source (such as zinc nitrate, ferric nitrate, tetraisopropoxytitanium, magnesium nitrate, potassium permanganate, silver nitrate, or bismuth nitrate), a small amount of ascorbic acid or citrate-based reducing agent is added. This allows for the preliminary complexation of some metal ions, stabilizing their valence states. Then, the solution is added dropwise simultaneously with a natural reducing agent and an alkaline solution at 80–90°C. The alkaline solution (NaOH, KOH, or ammonia) slowly raises the pH of the system to alkalinity, causing the metal ions to hydrolyze and generate hydroxyl complex intermediates. In this environment, natural polyphenols gradually reduce or encapsulate these hydrolyzed fragments, inducing uniform nucleation and limiting the crystal nucleus size, laying the foundation for obtaining highly dispersed nano-precursors.

[0022] S1.3. Detect the redox potential and pH value of the mixed solution. When the redox potential reaches the preset range, stop adding the oxidation precursor solution. When the pH value of the mixed solution reaches 10.0±0.1, stop adding the alkaline solution to obtain the reaction slurry. Both the metal source feed and the alkaline feed are added in an equal-incremental-time pattern. The former is controlled at 5~10 mL / min, while the latter is automatically and finely replenished with alkali according to the given pH window. The total alkali consumption and the amount of metal salt are maintained at a molar ratio of 2:1, thereby ensuring complete coordination of hydroxyl groups and a constant number of crystal nuclei.

[0023] By utilizing online oxidation-reduction potential (ORP) and pH dual closed-loop control, the metal source feed can be stopped immediately when the system potential enters a preset range (e.g., +50~+120mV), ensuring a dynamic equilibrium between the reduction reaction and complexation coating. Simultaneously, alkali supplementation is stopped when the pH reaches 10.0±0.1, precisely locking the nucleation number of metal hydroxyl precursors and the sol viscosity. This prevents large particle agglomeration caused by excessively rapid subsequent precipitation, achieving batch-to-batch reproducibility of particle size and phase composition, and providing a reliable mother liquor window for high-performance packed particles.

[0024] S1.4. Centrifuge the reaction slurry at 7000g for 10 minutes, discard the supernatant, resuspend in a mixture of water and ethanol, and sonicate for 2-3 minutes. Repeat the washing process three times to obtain a wet precipitate. During the washing stage, add 20 mL of water-ethanol (1:1, v / v) to each gram of wet precipitate for resuspension. After three centrifugations, the conductivity of the supernatant should be below 50 µS / cm. Based on 50g of initial precipitate, approximately 3 × 200 mL of the mixed solution is sufficient for the complete removal of salt ions and free organic matter.

[0025] Centrifugation at 7000g removes the supernatant and soluble byproducts. Then, resuspending the precipitate in water-ethanol (1:1) and washing it three times with ultrasound can simultaneously remove inorganic residues such as nitrate and chloride ions, as well as free polyphenol molecules, reducing the exothermic peak and carbon residue during subsequent calcination. Ethanol reduces surface tension and promotes secondary deagglomeration of the precursor, thus ensuring that the precipitate is loose and flocculent, creating conditions for freeze-drying and pore-forming treatment.

[0026] S1.5. Mix the template agent with the wet precipitate, freeze-dry to obtain a sheet, heat the sheet to 300℃ at 2℃ / min in air atmosphere, hold for 1 hour, then heat to 380℃ and hold for 30 minutes to obtain a sintered powder; the template agent includes at least one of pullulan, sodium alginate, and gum arabic. The amount of template agent added is controlled to be 0.5~1.0wt% of the dry solids of the wet precipitate. If the wet material contains 30g of solids, take 0.2g of pullulan (or the same amount of sodium alginate or gum arabic) and dissolve it in 100mL of water, mix it thoroughly with the precipitate, and then freeze (-40℃) and vacuum heat dry. The brittle sheet formed after freezing is heated to 300℃ at 2℃ / min and held for 1 hour, then heated to 380℃ and held for 30 minutes to ensure that the template is completely burned off and the grains are completely oxidized and phase-fixed.

[0027] Introducing pullulan, sodium alginate, or gum arabic into a wet precipitate followed by freeze-drying allows for the construction of a combustible framework at low temperatures. The freeze-dried flakes are then pre-calcined at 300°C to remove bound water and form oxide precursors. A subsequent short-term secondary calcination at 380°C completely ablates the organic template, resulting in a dense crystalline phase and ultimately leaving a network of interconnected micropores within the powder. This template-based porosity strategy significantly increases the specific surface area and the number of surface active sites, while simultaneously creating a rough mechanical interface on the particle surface. This allows for the formation of a robust nano-rivet interface when subsequently composited with a chitosan matrix.

[0028] S1.6. Ball mill the sintered powder for 5-10 minutes, sonicate for 10 minutes, and then vacuum dry at 60°C to obtain the filler particles. It is best to add 100 mL of isopropanol per 30 g of sintered powder, ball mill for 5-10 minutes (ceramic ball:powder mass ratio of 5:1), sonicate at 200 W for 10 minutes, and then vacuum dry at 60°C for 2 hours to obtain high specific surface activity filler particles with a particle size of 30-60 nm, a moisture content of <1%, which can be directly dispersed in the subsequent coating system.

[0029] Low-energy ball milling for 5-10 minutes combined with 10 minutes of ultrasonication effectively removes residual weak dimers from the sintered powder and further homogenizes the particle size distribution. Subsequent vacuum drying at 60°C removes adsorbed water and trace amounts of ethanol, exposing the particle surface with hydroxyl groups or small amounts of metallic hydroxyl groups. This not only maintains good dispersion and flowability but also provides polar sites for rapid wetting in the subsequent water-alcohol system. The resulting filled particles have a stable particle size of 30-60 nm, high specific surface area, and strong adhesion activity, enabling efficient construction of tortuous diffusion channels in the subsequent barrier layer and providing long-lasting antibacterial function.

[0030] S2. Mix the hard phase material and the soft phase material, add functional additives, and then melt extrude to obtain a masterbatch. Hot press the masterbatch to obtain the bottom film.

[0031] Step S2 includes: S2.1 The functional additives include compatibilizers, epoxy chain extenders, and bio-based antioxidants. First, the flexible phase material is mixed with the compatibilizer, then the hard phase material, epoxy chain extender, and bio-based antioxidant are added. The mixture is heated to 80°C and dried for 2 hours to obtain a mixed filler. The compatibilizer includes at least one of ethylene-butyl acrylate-glycidyl methacrylate, ethylene-methacrylate-glycidyl methacrylate, and epoxidized soybean oil. The epoxy chain extender includes bisphenol A type epoxy resin, Joncryl ADR- At least one of 4400, JoncrylADR-4440, and JoncrylADR-4368; bio-based antioxidants include at least one of vitamin E, vitamin C, ferulic acid, and ferulic palmitate; flexible phase materials include at least one of butylene terephthalate-butylene adipate copolymer, butylene succinate-butylene heptaate copolymer, polycaprolactone, and medium- and long-chain polyhydroxyalkanoates; and hard phase materials include at least one of polylactic acid, polyglycolic acid, and poly(3-hydroxybutyrate-3-hydroxyvalerate).

[0032] First, the flexible phase material (e.g., PBAT or PCL) is premixed with a reactive compatibilizer (EBA-GMA, EMAA-GMA, or epoxidized soybean oil). This allows the epoxy or anhydride groups in the compatibilizer to preferentially coat the flexible phase chain segments, reducing their surface tension. Then, hard phase polylactic acid (PLA) and multifunctional epoxy chain extenders (JoncrylADR series or bisphenol A type epoxy resin), as well as bio-based antioxidants such as vitamin E, vitamin C, and ferulic acid, are added. The compatibilizer is initially blended with the flexible phase during the 80℃ drying process for 2 hours. Drying removes moisture, and the antioxidants capture free radicals to inhibit early thermal degradation of the PLA, laying a uniform and stable reaction system for subsequent melt reaction extrusion.

[0033] S2.2 Place the mixed filler in a twin-screw extruder, set the temperatures of each zone of the barrel to 200℃, 195℃, 190℃, 185℃, 180℃, 175℃, and 170℃ respectively, set the die head temperature to 175℃, set the screw speed to 180~240rpm, set the vacuum pressure to -0.08MPa, extrude and water-cooled pellets, then pass through 80℃ hot air for 20min, and transfer to a drying oven at 50℃ for 2h to obtain masterbatch.

[0034] Under conditions of a gradient barrel temperature of 200-170℃, a screw speed of 180-240 rpm, and a vacuum of -0.08 MPa, a co-rotating twin-screw extruder provides high-shear mixing. The epoxy groups of the chain extender condense with polylactic acid and the terminal hydroxyl groups of the flexible phase, resulting in a simultaneous increase in number-average molecular weight and melt strength. Vacuum devolatilization promptly removes esterification byproduct water and low-molecular-weight acids, inhibiting reverse hydrolysis. After water-cooled stretching and shaping, the masterbatch is immediately subjected to two-stage drying: 20 minutes of hot air at 80℃ and 2 hours of vacuum at 50℃, reducing the moisture content of the masterbatch to <0.05 wt%, ensuring stable viscoelastic window and no yellowing during hot pressing.

[0035] S2.3. Obtain a low-layer film of a predetermined thickness by melt extrusion casting of the masterbatch; The specific steps are as follows: Place the masterbatch back into the twin-screw extruder. Configure a 60 / 120 / 60 mesh stacked screen and a flat die with a width of 1000~1500 mm at the front end of the twin-screw extruder. The thickness is controlled according to t=Q / (ρ·W·v) (t is the thickness in cm, Q is the extrusion rate in g / min, and ρ can be 1.24 g / cm). -3 , represents the masterbatch density, W is the effective width in cm, v is the linear velocity in cm / min, and different preset thickness levels can be achieved through Qv linkage.

[0036] A mirror-finish cooling roller with a temperature of 15-25℃ and a wrap angle of approximately 180° is used to suppress haze and refine grains. The secondary traction roller forms a tension band of 5-15 N / m with the cooling roller, preventing chatter and wrinkling. The cleanliness and temperature stability of the roller surface directly determine the appearance and thickness texture. In actual production, maintaining constant Q and variable v is prioritized, making thickness control easier through a closed-loop process.

[0037] In one embodiment, S2.3 may be: spreading the masterbatch into the mold cavity of a flat hot press, preheating it to 190°C, holding it for 60s, increasing the pressure to 6MPa and holding it for 120s to completely melt and degas, restoring it to normal pressure and holding it for 10s, then increasing the pressure to 6MPa and holding it for 10s, and then water cooling it to 30°C at 6MPa to demold it, thus obtaining the bottom film.

[0038] The masterbatch is preheated at 190°C for 60 seconds in a flatbed hot press to soften the surface layer. Then, it is held at 6 MPa for 120 seconds to induce the formation of a continuous hard phase from polylactic acid. The soft phase is sheared and stretched into fine, resilient islands, and the phase interface is chemically grafted with a compatibilizer. Depressurization for 10 seconds followed by repressurization removes residual air bubbles and prevents pinholes and streaks. Water cooling to 30°C while maintaining 6 MPa rapidly overcomes the Tg threshold, locking the chain orientation and refining the grains to obtain a dense bottom film with a thickness tolerance of <±5%.

[0039] S2.4. Stretch the bottom film unidirectionally by 1.8 to 2.2 times at a stretching table at 70 to 80°C, then heat it to 110°C and hold for 10 minutes for annealing.

[0040] The base film is uniaxially stretched by 1.8 to 2.2 times at 70–80°C, which orients the polylactic acid backbone along the stretching direction and stretches the flexible island chains into long strips and further disperses them. Subsequently, annealing at 110°C for 10 min induces the formation of α-crystals and a small amount of stereocomposite crystals, significantly improving the yield strength, puncture strength, and heat-sealing limit. At the same time, the internal residual stress is fully eliminated, and the heat shrinkage rate can be controlled to ≤1%. Finally, a biodegradable base film with high modulus, heat resistance, and excellent toughness is obtained, providing stable mechanical support and a heat-sealing substrate for subsequent barrier layers, color development layers, and topcoat functional layers.

[0041] In one embodiment, taking a 100kg polymer system as an example, 70kg of hard phase polylactic acid (PLA) and 30kg of flexible phase toughening resin (e.g., PBAT, PBSA, or PCL) are used. The 70:30 mass ratio of the two ensures that the continuous phase is still dominated by PLA while significantly improving toughness. In the additives section, approximately 3kg of reactive compatibilizer is first added to the flexible phase. Epoxy-containing compounds such as EBA-GMA, EMAA-GMA, or epoxidized soybean oil can be selected. The amount used is equivalent to 3 phr of the resin mass, sufficient to graft with the end groups of both phases during melt extrusion, weakening interfacial tension. Subsequently, 1.2kg of multifunctional epoxy chain extender, corresponding to 1~1.5 phr, is added, which can significantly improve the number-average molecular weight and melt strength. To suppress free radical degradation caused by high-temperature shear and hydrolysis, 0.25kg of bio-based antioxidant (vitamin E, vitamin C, or ferulic acid derivatives), approximately 0.25 phr, is added to maintain color and viscoelastic properties stability at reactive extrusion temperatures around 200°C. The masterbatch obtained by formulating, vacuum reactive extrusion, subsequent water-cooled pelletizing, and drying processes reduces the melt flow rate from 6 g / 10 min of the original PLA to about 3.5 g / 10 min. This ensures the flowability during hot pressing, provides the bottom film with a tensile strength of ≥45 MPa and an elongation of 60~80%, and retains a heat-sealable window above 130℃ to meet the low-temperature composite requirements of the subsequent barrier layer, color development layer, and topcoat layer.

[0042] S3. Mix the filler particles with the dispersion solvent to obtain a filler sol. Coat the filler sol onto the surface of the bottom film to form a barrier layer. Coat the barrier layer with a color developing film and a waterproof coating film in sequence to obtain a biodegradable film packaging material.

[0043] Step S3 includes: S3.1 Add the filler particles to the dispersion solvent, adjust the rotation speed to 8000~10000 rpm, rotate for 5~10 min, add the binder and then perform ultrasonic dispersion, ultrasonic power of 200~400W, ultrasonic for 10~20 min to obtain the filler sol, adjust the pH of the filler sol to 4.5~5.0, and adjust the viscosity of the filler sol at 25℃ to 60~150 mPa·s; the dispersion solvent includes at least one of polyvinylpyrrolidone, ammonia, sodium dodecyl sulfate, and polyvinyl alcohol.

[0044] Under high shear at 8000~10000 rpm, the surface-active groups of the dispersion solvent (PVP, NH3·H2O, SDS or PVA) preferentially adsorb onto the surface of the filler particles, establishing a preliminary steric or electrostatic repulsion barrier. Then, chitosan binder is added and the mixture is sonicated at 200~400W for 10~20 min for redispersibility, allowing the stabilized nanoparticles to be uniformly embedded into the chitosan network. Finally, the sol pH is adjusted to 4.5~5.0, and the viscosity (25℃) is controlled at 60~150 mPa·s. This not only ensures that subsequent coatings do not drip or have pinholes, but also prevents premature cross-linking of chitosan and maintains the surface activity of CuO, forming a functional coating with long-term suspension stability and moderate thixotropy.

[0045] S3.2. Apply the filler sol to the bottom film and then blow it with hot air at 60℃ for 3~5 minutes to form a barrier layer.

[0046] After the above-mentioned filler sol is evenly coated onto the bottom film, the water / ethanol is rapidly evaporated by hot air at 60℃ for 3-5 minutes. The chitosan continuous phase shrinks and binds to the corona-activated PLA / PBAT surface through hydrogen bonds; the nano-oxides form nano-rivet-like interlocking in the chain network, establishing tortuous diffusion channels. Because the slow release of copper ions has a significant inhibitory effect on molds and Gram-negative bacteria, it achieves multiple synergistic effects of mechanical, barrier, and antibacterial properties.

[0047] S3.3. Dissolve red cabbage anthocyanin powder in an acidic solution to obtain an anthocyanin solution. Mix pullulan, gum arabic, and glycerol in deionized water, heat to 50°C, and stir for 20 minutes to obtain a wall material solution. Mix the anthocyanin solution and the wall material solution, adjust the rotation speed to 8000 rpm for pre-emulsification for 3 minutes, and then sonicate at 200W ultrasonic power for 2 minutes to obtain an emulsion. The acidic solution includes at least one of citrate-sodium citrate buffer, lactic acid solution, and glacial acetic acid dilution.

[0048] Anthocyanins can be stabilized by dissolving them in citrate buffer, lactic acid solution, or glacial acetic acid dilution. The wall material solution is formed by stirring pullulan, gum arabic, and glycerol at 50°C for 20 min to create a viscoelastic matrix. The two solutions are pre-emulsified at 8000 rpm for 3 min and then sonicated at 200 W for 2 min to obtain an emulsion with uniform particle size. The wall material can rapidly encapsulate anthocyanins and reduce their sensitivity to heat, light, and metal ions under acidic conditions, providing a uniform precursor solution for subsequent spray drying.

[0049] S3.4 The emulsion is fed into the spray drying tower at a rate of 6 mL / min using a peristaltic pump. The inlet temperature of the tower is set at 160℃, and the outlet temperature is set at 80℃. Atomization is achieved using a 0.7 mm dual-fluid nozzle, compressed air at 0.25 MPa, and hot air flow rate at 0.35 m³ / min. 3 / min, to obtain spherical microcapsule powder, mix the spherical microcapsule powder with citric acid solution, adjust the rotation speed to 8000rpm for pre-emulsification for 3min, and then sonicate with 200W ultrasonic power for 2min to obtain colorimetric film solution.

[0050] The emulsion enters the spray tower at a rate of 6 mL / min, where it is atomized in conjunction with 0.25 MPa compressed air at a 160°C inlet. Moisture evaporates rapidly, pullulan forms a shell first, and gum arabic interweaves on the outer layer, plasticized by glycerol, solidifying into spherical microcapsules with a diameter of approximately 5 µm within 2 seconds. Maintaining an outlet temperature of 80°C maximizes the preservation of anthocyanin activity. The dry powder is then emulsified a second time with citric acid solution, followed by sonication to form a colorimetric film. Citric acid complexes a small amount of metal ions on the outer wall of the capsules, precisely locking the colorimetric threshold at approximately pH 5.5, achieving rapid color change triggered by both spoilage and breakage.

[0051] S3.5. Apply the color-developing film solution to the barrier layer, heat to 50°C and hold for 5 minutes, then apply the waterproof coating film solution, heat to 80°C, and dry for 10-20 minutes to obtain the biodegradable film packaging material. The waterproof coating film solution includes at least one of beeswax-carnauba wax composite emulsion, shellac ethanol solution, and polycaprolactone ethyl acetate solution.

[0052] A color-developing film is coated onto the barrier layer and baked at 50°C for 5 minutes to form a pullulan-ginger arabic film, which then forms a polysaccharide-polysaccharide interface with the underlying chitosan layer. The coating thickness is approximately 1 µm, and it responds to pH or mechanical stress within 5–10 minutes. Subsequently, one of the following solutions—beeswax-carnauba wax emulsion, shellac ethanol solution, or PCL-ethyl acetate solution—is sprayed on and dried at 80°C for 10–20 minutes to form a continuous hydrophobic coating. This coating provides excellent barrier properties against external water, gasoline, and grease without hindering the permeation of volatile acids and alkalis. With the three layers working synergistically, the film simultaneously provides mechanical support, gas barrier properties, long-lasting antibacterial properties, visible warning of damage and spoilage, and surface stain resistance. Furthermore, all raw materials are derived from biodegradable or compostable systems, meeting the full life-cycle sustainability requirements of biodegradable packaging.

[0053] The anthocyanin microcapsules in the color-developing film are extremely sensitive to pH: when the food inside the packaging releases organic acids or alkalis due to microbial spoilage, causing the local pH to exceed a set threshold (≈5.5), the microcapsule walls break or the anthocyanin structure ionizes, and the film color changes from purple to green. Consumers or logistics personnel can determine whether the contents are still safe to eat without opening the packaging. The color-developing film is designed in the sentinel graphic area around the edges of the film that are susceptible to impact, puncture, or heat sealing. When the packaging material is punctured by external force during transportation, handling, or storage, mechanical shearing will immediately destroy the microcapsule shell, instantly exposing and coloring the anthocyanins, visually marking the damage point; cold chain and express delivery links can use this to quickly sort and claim compensation, reducing the risk of secondary contamination caused by microcracks. By adjusting the anthocyanin source, microcapsule particle size, and wall material ratio, different color development thresholds and chromatographic response curves can be customized; combined with printed QR codes or logos, a dynamic color fingerprint that is difficult to replicate can be formed, providing both quality traceability and anti-counterfeiting functions. The machine vision system on the production line can also detect the baseline color difference of the color developing film in real time, as part of the online quality control threshold, to ensure batch-to-batch consistency.

[0054] In one embodiment, when preparing the filler sol, 1 L of water-ethanol (1:1, v / v) was used as the dispersion system. First, 15 g of nanofiller particles (1.5 wt% of the total mass) were added, and after high-speed shearing for 5 min, 0.5 g of PVP (0.05 wt%) was added as a steric hindrance stabilizer. Then, 100 mL of a 1 wt% chitosan solution was slowly added dropwise, so that the final chitosan content in the system was approximately 1 wt%. Subsequently, the system was sonicated for 15 min, and the pH was adjusted to 4.5-5.0 using glacial acetic acid. The viscosity at 25°C was adjusted to 80 mPa·s, resulting in a functional sol that could be suspended for a long time. When coating the barrier layer, 8 mL of m... -2 The wet coating amount is used to coat the above-mentioned sol onto the surface of the underlying film; after the coating with a solid content of 6wt% is heated by hot air at 60°C for 4 minutes, all the solids are formed into a film, which is equivalent to a dry coating amount of 0.5gm. -2 Of which chitosan ≈ 0.05 gm -2 Filler particle size ≈ 0.075gm -2This method can achieve a barrier enhancement effect by reducing WVTR and OTR by approximately 60% and 35%, respectively. In preparing the chromogenic microcapsules, 2g of red cabbage anthocyanin was first dissolved in 100mL of citrate-sodium citrate buffer (pH 3.0); separately, 6g of Pullulan, 2g of gum arabic, and 0.5g of glycerol were dissolved in 86mL of deionized water, and stirred at 50°C for 20min to obtain a wall material solution. The solutions were combined at a core material:wall material ratio of 1:2 (w / w), pre-emulsified at 8000rpm for 3min, and sonicated at 200W for 2min to obtain a homogeneous emulsion with 15wt% solids. This emulsion was then spray-dried (inlet 160°C / outlet 80°C) to obtain spherical microcapsule powder with an average particle size of 5µm. When preparing the colorimetric film solution, add 10g of microcapsule powder to 100mL of 0.1wt% citric acid aqueous solution, emulsify at 8000rpm for 3min, and sonicate at 200W for 2min to stabilize the solid content at 10wt% and the viscosity at 100mPa·s; the wet film volume for screen printing is 6mL / m. 2 After drying at 50°C for 5 minutes, a 1µm thick colorimetric layer was formed, with the pH trigger threshold precisely locked at 5.5. Finally, a 1.0wt% beeswax-carnauba wax emulsion was applied at a depth of 5mL / m². 2 Dry at 80°C for 15 minutes; dry coating amount: 0.05 g / m² 2 This wax-phase continuous film can increase the surface hydrostatic contact angle to ≥90°, and has moisture-proof and oil-proof properties without cross-linking. It fully retains the color development and barrier properties of the lower layer, thus obtaining a biodegradable film packaging material with mechanical support, gas barrier, long-lasting antibacterial and visual warning functions.

[0055] This invention proposes a biodegradable film packaging material, which is prepared by a method for making biodegradable film packaging materials.

[0056] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a biodegradable film packaging material, characterized in that the steps include... include: S1. Mix the natural reducing agent and the oxidation precursor solution, adjust the pH of the mixed solution to alkaline, heat and stir, centrifuge, and calcine the precipitate to obtain the filled particles; S2. Mix the hard phase material and the soft phase material, add functional additives, and then melt extrude to obtain a masterbatch. Hot press the masterbatch to obtain the bottom film. S3. The filler particles are mixed with the dispersion solvent to obtain a filler sol. The filler sol is coated on the surface of the bottom film to form a barrier layer. A color-developing film and a waterproof coating film are coated sequentially on the barrier layer to obtain a biodegradable film packaging material, wherein the color-developing film includes anthocyanins.

2. The method for preparing a biodegradable film packaging material according to claim 1, characterized in that, Step S1 includes: S1.1 Mix natural plant powder with deionized water, heat to 80℃ and stir for 60 minutes, then hot filter to obtain natural reducing agent. Adjust the pH of natural reducing agent to neutral. S1.2 Add a reducing agent to the metal source solution to obtain an oxidation precursor solution. Simultaneously add the oxidation precursor solution and an alkaline solution to the natural reducing agent and maintain the temperature at 80~90℃. S1.3 Detect the redox potential and pH value of the mixed solution. When the redox potential reaches the preset range, stop adding the oxidation precursor solution. When the pH value of the mixed solution reaches 10.0±0.1, stop adding the alkaline solution and obtain the reaction slurry. S1.4 Centrifuge the reaction slurry at 7000g for 10 minutes, discard the supernatant, resuspend it in a mixture of water and ethanol and sonicate for 2-3 minutes. Repeat the washing process 3 times to obtain a wet precipitate. S1.

5. Mix the template agent in the wet precipitate, freeze-dry to obtain a sheet, heat the sheet to 300℃ at 2℃ / min in air atmosphere, hold for 1h, then heat to 380℃ and hold for 30min to obtain sintered powder. S1.

6. The sintered powder is ball-milled for 5-10 minutes, sonicated for 10 minutes, heated to 60℃ and vacuum dried to obtain the filling particles.

3. The method for preparing a biodegradable film packaging material according to claim 2, characterized in that, In step S1, the natural plant powder includes at least one of fig powder, pomegranate peel powder, green tea powder, and grape seed powder; the metal source solution includes at least one of zinc source, iron source, titanium source, magnesium source, manganese source, silver source, and bismuth source; the zinc source includes at least one of zinc nitrate hexahydrate, zinc acetate dihydrate, zinc sulfate heptahydrate, zinc chloride, and zinc acetylacetonate; the iron source includes at least one of ferric nitrate nonahydrate, ferric chloride hexahydrate, ferrous sulfate heptahydrate, ferric citrate, and ferric acetylacetonate; and the titanium source includes at least one of tetraisopropoxy titanium, tetrabutoxy titanium, tetraethoxy titanium, titanium tetrachloride, and titanium oxalate ammonium. The magnesium source includes at least one of magnesium nitrate hexahydrate, magnesium sulfate heptahydrate, magnesium acetate tetrahydrate, magnesium chloride hexahydrate, and magnesium oxalate dihydrate; the manganese source includes at least one of manganese nitrate tetrahydrate, manganese chloride tetrahydrate, manganese acetate tetrahydrate, manganese sulfate monohydrate, and potassium permanganate; the silver source includes at least one of silver nitrate, silver acetate, silver perchlorate, silver trifluoroacetate, and diamine silver complex; the bismuth source includes at least one of bismuth nitrate pentahydrate, bismuth chloride, bismuth acetate, bismuth subnitrate, basic bismuth nitrate, and bismuth citrate; and the template agent includes at least one of pullulan, sodium alginate, and gum arabic.

4. The method for preparing a biodegradable film packaging material according to claim 1, characterized in that, Step S2 includes: S2.1 The functional additives include compatibilizers, epoxy chain extenders and bio-based antioxidants. First, the flexible phase material and compatibilizer are mixed, and then the hard phase material, epoxy chain extender and bio-based antioxidant are added. The mixture is heated to 80°C and dried for 2 hours to obtain the mixed filler. S2.2 Place the mixed filler in a twin-screw extruder, set the temperatures of each zone of the barrel to 200℃, 195℃, 190℃, 185℃, 180℃, 175℃, and 170℃ respectively, set the die head temperature to 175℃, set the screw speed to 180~240rpm, set the vacuum pressure to -0.08MPa, extrude and water-cooled pellets, then pass through 80℃ hot air for 20min, and transfer to a drying oven at 50℃ for 2h to obtain masterbatch; S2.3, The masterbatch is melt-extruded and cast to obtain a low-layer film of a predetermined thickness [1]; S2.

4. Stretch the bottom film unidirectionally by 1.8 to 2.2 times at a stretching table at 70 to 80°C, then heat it to 110°C and hold for 10 minutes for annealing.

5. The method for preparing a biodegradable film packaging material according to claim 4, characterized in that, In step S2, the compatibilizer includes at least one of ethylene-butyl acrylate-glycidyl methacrylate, ethylene-methacrylate-glycidyl methacrylate, and epoxidized soybean oil; the epoxy chain extender includes at least one of bisphenol A epoxy resin, Joncryl ADR-4400, Joncryl ADR-4440, and Joncryl ADR-4368; the bio-based antioxidant includes at least one of vitamin E, vitamin C, ferulic acid, and ferulic acid palmitate; the flexible phase material includes at least one of butylene terephthalate-butylene adipate copolymer, butylene succinate-butylene heptahydrate copolymer, polycaprolactone, and medium- and long-chain polyhydroxyalkanoates; and the hard phase material includes at least one of polylactic acid, polyglycolic acid, and poly(3-hydroxybutyrate-3-hydroxyvalerate).

6. The method for preparing a biodegradable film packaging material according to claim 1, characterized in that, Step S3 includes: S3.1 Add the filler particles to the dispersion solvent, adjust the rotation speed to 8000~10000rpm, rotate for 5~10min, add the binder and then perform ultrasonic dispersion, ultrasonic power of 200~400W, ultrasonic for 10~20min to obtain the filler sol, adjust the pH of the filler sol to 4.5~5.0, and adjust the viscosity of the filler sol at 25℃ to 60~150mPa·s; S3.

2. Apply the filler sol to the bottom film and then blow it with 60℃ hot air for 3~5 minutes to form a barrier layer; S3.3 Dissolve red cabbage anthocyanin powder in an acidic solution to obtain anthocyanin solution. Mix pullulan, gum arabic, and glycerin in deionized water, heat to 50°C and stir for 20 minutes to obtain wall material solution. Mix the anthocyanin solution and wall material solution, adjust the rotation speed to 8000 rpm for pre-emulsification for 3 minutes, and then sonicate with 200W ultrasonic power for 2 minutes to obtain emulsion. S3.4 The emulsion is fed into the spray drying tower at a rate of 6 mL / min using a peristaltic pump. The inlet temperature of the tower is set at 160℃, and the outlet temperature is set at 80℃. Atomization is achieved using a 0.7 mm dual-fluid nozzle, compressed air at 0.25 MPa, and hot air flow rate at 0.35 m³ / min. 3 / min, to obtain spherical microcapsule powder, mix the spherical microcapsule powder with citric acid solution, adjust the rotation speed to 8000 rpm for pre-emulsification for 3 min, and then sonicate with 200W ultrasonic power for 2 min to obtain colorimetric film solution; S3.

5. Coat the color developing film solution onto the barrier layer, heat to 50℃ and hold for 5 minutes, then coat with the waterproof coating film solution, heat to 80℃ and dry for 10~20 minutes to obtain the biodegradable film packaging material.

7. The method for preparing a biodegradable film packaging material according to claim 6, characterized in that, In step S3, the dispersing solvent includes at least one of polyvinylpyrrolidone, ammonia, sodium dodecyl sulfate, and polyvinyl alcohol; the acidic solution includes at least one of citric acid-sodium citrate buffer, lactic acid solution, and glacial acetic acid dilution; and the waterproof coating film solution includes at least one of beeswax-carnauba wax composite emulsion, shellac ethanol solution, and polycaprolactone ethyl acetate solution.

8. A biodegradable film packaging material, characterized in that, It is prepared by the method of any one of claims 1-7 for preparing a biodegradable film packaging material.

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