Pha food packaging material and method of preparation

Abstract

The application discloses a kind of PHA food packaging materials and preparation method, it is related to petrochemical chemical new material technical field, by the following weight parts of raw materials are made: medium long chain PHA 60-75 parts, carbon dioxide copolymer 20-30 parts, KH-550 modified silicon dioxide 3-8 parts, plant essential oil antibacterial microcapsule 1-3 parts, polycaprolactone plasticizing microcapsule 1-2 parts, food-grade stabilizer 0.1-0.5 parts, dynamic crosslinking agent 0.5-1 part.In the application, by the synergistic technical scheme of high molecular compound modification, inorganic filler surface activation, functional component microcapsule coating, the internal structure and interface bonding state of material are optimized from the root, the defects that traditional PHA matrix is prone to phase separation, weak mechanical property, insufficient thermal stability are improved, the overall stability and environmental adaptability of material are significantly improved, can satisfy the use scene demand of diversified food packaging.

Description

Technical Field

[0001] This invention relates to the field of petrochemical new materials technology, specifically to a PHA food packaging material and its preparation method. Background Technology

[0002] Driven by dual carbon targets, petrochemical new materials are accelerating their transformation towards low-carbon, recyclable, and high-safety technologies. Green alternatives to traditional petroleum-based plastics (such as PE, PP, and PET) have become a core research and development direction for the industry. The food packaging sector, being directly related to food safety and environmental sustainability, has a particularly urgent need for environmentally friendly packaging materials. Among them, PHA (polyhydroxyalkanoate), as a type of natural high-molecular polyester synthesized by microorganisms through fermentation, has core characteristics such as being entirely bio-based, completely biodegradable, and having excellent biocompatibility. Its degradation products are water and carbon dioxide, which will not cause secondary pollution to the environment. It is recognized globally as the most promising alternative in this field, which aligns with the current transformation trend of petrochemical new materials.

[0003] However, in existing technologies, PHA-based petrochemical new materials for food packaging are prone to micro-phase separation during long-term storage or temperature changes due to the inherent polarity differences between PHA, PLA, and inorganic fillers. This leads to brittleness and cracking. Furthermore, their thermal stability is insufficient, making them unsuitable for diverse food packaging scenarios. In terms of safety, some solutions use heavy metal antibacterial agents or directly add uncoated antibacterial agents and plasticizers. The former can easily lead to the risk of heavy metal accumulation, while the latter can cause excessive migration of active ingredients, both of which violate food contact safety requirements. On the recycling end, due to the lack of precise sorting technology and reversible cross-linking design, PHA packaging is difficult to separate from other wastes efficiently, and aged materials cannot achieve efficient depolymerization and regeneration. The recycling purity and utilization rate are low, resulting in resource waste. These problems collectively restrict the industrialization, promotion, and large-scale application of this type of petrochemical new material. Summary of the Invention

[0004] The purpose of this invention is to provide a PHA food packaging material and its preparation method to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a PHA food packaging material, made from the following raw materials in parts by weight: 60-75 parts of medium- and long-chain PHA, 20-30 parts of carbon dioxide copolymer, 3-8 parts of KH-550 modified silica, 1-3 parts of plant essential oil antibacterial microcapsules, 1-2 parts of polycaprolactone plasticizing microcapsules, 0.1-0.5 parts of food-grade stabilizer, and 0.5-1 parts of dynamic crosslinking agent.

[0006] Preferably, the medium- and long-chain PHA is a copolymer or blend of polyhydroxyhexanoic acid and polyhydroxyoctanoic acid, and the carbon dioxide copolymer is a composite system of polypropylene carbonate and polypropylene carbonate-ethylene oxide composite copolymer.

[0007] Preferably, the wall material of the plant essential oil antibacterial microcapsules is a mixture of alginate and chitosan, with a weight ratio of alginate to chitosan of 7:5, and the core material is ginger essential oil; the encapsulation rate of the plant essential oil antibacterial microcapsules is not less than 90%, and the particle size is 10-50 micrometers.

[0008] Preferably, the wall material of the polycaprolactone plasticized microcapsules is a mixture of whey protein and pectin, with an encapsulation rate of not less than 85%.

[0009] Preferably, the dynamic crosslinking agent is a thioctin analogue, and the food-grade stabilizer is a food contact grade additive that can delay the oxidative degradation of PHA.

[0010] A method for preparing a PHA food packaging material includes the following steps: S1. Pretreatment: including modified silica preparation, microcapsule preparation and PHA purification; S11. Preparation of modified silica: Add silica powder to anhydrous ethanol and ultrasonically disperse for 30 minutes to form a suspension; add KH-550 (3% by mass of silica) to the suspension, and stir at 70℃ for 6 hours at a stirring rate of 200-300 rpm; after the reaction, centrifuge at 3000-4000 rpm for 10 minutes to separate the solid particles, wash with anhydrous ethanol 3-4 times until no amino groups are detected in the supernatant, and dry at 80℃ and -0.08 to -0.09 MPa for 12 hours until the moisture content is not higher than 0.5% to obtain KH-550 modified silica; S12. Microcapsule preparation: Plant essential oil antibacterial microcapsules and polycaprolactone plasticized microcapsules were prepared by a composite coagulation method. Among them, the plant essential oil antibacterial microcapsules were mixed with the wall material and the core material at a weight ratio of 3:1 and the pH value was adjusted to 4.0-4.5. The polycaprolactone plasticized microcapsules were prepared by the same composite coagulation method. S13, PHA Refining: The PHA obtained from fermentation is broken down, concentrated by centrifugation, and then vacuum dried until the moisture content is no higher than 0.5%; S2, Blending Molding: including premixing, melt blending and molding processing; S21. Premixing: Add medium- and long-chain PHA, carbon dioxide copolymer, KH-550 modified silica, food-grade stabilizer and dynamic crosslinking agent into a high-speed mixer and stir at 100-110℃ for 15 minutes at a speed of 300-400 rpm. S22. Melt blending: Add the premix to a twin-screw extruder, set the gradient temperature zone 1 to 145-155℃, zone 2 to 160-170℃, and zone 3 to 170-180℃, and the screw speed to 280-320 rpm. Add plant essential oil antibacterial microcapsules and polycaprolactone plasticizing microcapsules, and extrude and granulate. S23. Molding process: Add the granules to an injection molding machine or blow molding machine for molding. The injection temperature is 165-175℃, the blow molding air pressure is 0.6-0.8 MPa, and the cooling time is 15-20 seconds. S3. Post-processing and closed-loop recycling: S31. Post-processing: The molded products are subjected to medium-wave infrared annealing, with a heating rate of 3-5℃ per minute and a holding time of 55-60℃ for 30 minutes. The surface is printed with biodegradable markings, material codes and recycling markings. S32, Closed-loop recycling: Includes crushing and screening, conveying and scanning, intelligent sorting, purity detection and dual-path recycling steps.

[0011] Preferably, the preparation of the plant essential oil antibacterial microcapsules in step S12 further includes the following specific steps: A1. Raw material dissolution and core material emulsification: Alginate is added to deionized water to prepare a 1.5% to 2.0% aqueous solution, and chitosan is added to a 1% dilute acetic acid aqueous solution to prepare a 1.0% to 1.5% aqueous solution; ginger essential oil is added to the alginate aqueous solution, and the mixture is homogenized at high speed for 15-20 minutes or ultrasonically emulsified to disperse it into droplets of 1-5 micrometers. A2. Coagulation: Add the chitosan aqueous solution dropwise to the emulsion at a rate of 1-2 ml per minute, stir at 300-400 rpm and adjust the pH to 4.0-4.5; A3. Curing: Add 1.0% to 2.0% calcium chloride solution, the amount of which is 5% to 8% of the total mass of the wall material. Stir and react for 30 minutes, then let it stand and age for 1 hour. A4. Separation and drying: Centrifuge at 3000 rpm for 10 minutes, wash the precipitate 3 times with deionized water, and dry at 60℃ and -0.08 MPa for 8 hours until the moisture content is no higher than 1%.

[0012] Preferably, in step S22, the plant essential oil antibacterial microcapsules and polycaprolactone plasticized microcapsules are added through the side feed port of the second zone of the twin-screw extruder.

[0013] Preferably, the specific steps of closed-loop recycling in step S32 are as follows: B1. Crushing and Screening: The recycled PHA packaging is crushed into particles of 5-20 mm and passed through a 10-mesh sieve to remove large impurities. B2. Conveying and Scanning: The crushed material is conveyed at a constant speed by a belt conveyor, and the multispectral imaging system above scans each particle 360°, simultaneously collecting spectral data and location information. B3. Intelligent Judgment and Sorting: The machine learning model analyzes spectral data in real time and marks the position of PHA particles. When the particles reach the sorting area, the high-pressure air jet device accurately blows out the PHA particles, which fall into a dedicated recycling bin. Other waste continues to be transported to the ordinary waste bin. B4. Purity Detection and Feedback: A secondary spectral detection is set at the outlet of the recycling bin. If the purity does not reach 98%, the system automatically adjusts the spectral recognition threshold to optimize the sorting accuracy. B5. Dual-path recycling: Recyclable particles without obvious aging are directly subjected to physical recycling and granulation; Severely aged waste materials are put into the recycling reactor, and 5% of ethylene glycol by mass is added as a depolymerizing agent at 180-200℃ and 0.3-0.5 MPa. After depolymerization for 4 hours, regeneration polymerization is carried out at 160-170℃ under a nitrogen atmosphere.

[0014] Preferably, in step B2, the multispectral imaging system includes a visible light camera, a near-infrared camera, and a mid-infrared camera, which acquires characteristic absorption peak data of PHA in the near-infrared band at 1.70-1.76 μm and the mid-infrared band at 5.7-5.9 μm; in step B3, the machine learning model is established based on the characteristic spectrum of PHA.

[0015] Compared with the prior art, the beneficial effects of the present invention are: 1. In this invention, a synergistic technical solution of polymer compound modification, inorganic filler surface activation, and functional component microcapsule encapsulation is adopted to fundamentally optimize the internal structure and interface bonding state of the material. This improves the defects of traditional PHA matrix, such as easy phase separation, weak mechanical properties, and insufficient thermal stability, and significantly enhances the overall stability and environmental adaptability of the material. It can meet the needs of diverse food packaging application scenarios. At the same time, natural plant essential oils are used to replace heavy metal antibacterial agents, eliminating the safety hazards caused by heavy metal migration from the source. Combined with the barrier and slow-release design of composite wall material, the migration rate of functional additives is effectively controlled, ensuring the safety of food contact throughout the entire process. This achieves a synergistic improvement in the mechanical properties, thermal properties, and food safety of the material, breaking through the bottleneck of existing technology where performance and safety are difficult to balance. The overall technical effect is far superior to traditional modification solutions. 2. This invention introduces a reversible dynamic cross-linking structure, ensuring both material strength and structural stability while achieving controllable depolymerization and regeneration during the recycling process, significantly improving the material's recyclability. Intelligent and precise sorting technology replaces traditional sorting methods, effectively improving the sorting efficiency and recycling purity of waste packaging. It enables the classification and dual-path regeneration of waste materials with varying degrees of loss, increasing resource utilization. Furthermore, the entire technical solution fully preserves the inherent biodegradable characteristics of PHA materials while achieving recycling, ensuring that its environmentally friendly nature is not compromised by modification and regeneration. This solution aligns with the low-carbon and recyclable development direction of new petrochemical materials, perfecting the industrial application chain of PHA packaging materials and possessing significant industrial promotion value and environmental benefits. Attached Figure Description

[0016] Figure 1 This is a flowchart of a PHA food packaging material and its preparation method according to the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] The present invention will be further described below with reference to embodiments.

[0019] Example 1: Please refer to Figure 1 As shown, a PHA food packaging material is made from the following raw materials in parts by weight: 70 parts of medium- and long-chain PHA (a copolymer of polyhydroxyhexanoic acid and polyhydroxyoctanoic acid), 25 parts of carbon dioxide copolymer (polypropylene carbonate and polypropylene carbonate-ethylene oxide composite copolymer), 5 parts of KH-550 modified silica, 2 parts of plant essential oil antibacterial microcapsules, 1 part of polycaprolactone plasticizing microcapsules, 0.3 parts of food-grade stabilizer, and 0.7 parts of dynamic crosslinking agent (lipoic acid analogue).

[0020] Among them, the wall material of the plant essential oil antibacterial microcapsules is alginate and chitosan (weight ratio 7:5), the core material is ginger essential oil, the encapsulation rate is ≥90%, and the particle size is 10-50μm; the wall material of the polycaprolactone plasticized microcapsules is whey protein and pectin, with an encapsulation rate of ≥85%.

[0021] A method for preparing PHA food packaging material: S1. Preprocessing: S11. Preparation of modified SiO2: SiO2 powder was added to anhydrous ethanol and ultrasonically dispersed for 30 minutes to form a suspension; KH-550 (3% by mass of SiO2) was added to the suspension and stirred at 70℃ for 6 hours (stirring rate 200-300 r / min); after the reaction, the mixture was centrifuged at 3000-4000 r / min for 10 minutes to separate the solid particles, washed 3-4 times with anhydrous ethanol until no amino groups were detected in the supernatant, and dried at 80℃ and -0.08 to -0.09 MPa for 12 hours until the moisture content was ≤0.5% to obtain KH-550 modified SiO2; S12. Microcapsule preparation: Antibacterial microcapsules were prepared using a composite coagulation method, with the wall material and core material mixed at a weight ratio of 3:1, and the pH adjusted to 4.0-4.5; Plasticizing microcapsules were prepared using the same composite coagulation method. S13, PHA Refining: The PHA obtained from fermentation is broken down, concentrated by centrifugation, and then vacuum dried to a moisture content of ≤0.5%; S2, Blending Molding: S21. Premixing: Add medium- and long-chain PHA, carbon dioxide copolymer, KH-550 modified SiO2, food-grade stabilizer and dynamic crosslinking agent into a high-speed mixer and stir at 100-110℃ for 15 minutes (300-400r / min). S22. Melt blending: Add the premixed material to a twin-screw extruder, set the gradient temperature (zone 1 145-155℃, zone 2 160-170℃, zone 3 170-180℃), and the screw speed is 280-320 r / min. Add the two microcapsules from the side of zone 2 to the feeding port, and extrude and granulate. S23. Molding process: Add the granules to an injection molding machine or blow molding machine for molding. The injection temperature is 165-175℃, the blow molding air pressure is 0.6-0.8MPa, and the cooling time is 15-20 seconds. S3. Post-processing and closed-loop recycling: S31. Post-processing: The molded products are subjected to medium-wave infrared annealing (heating rate 3-5℃ / min, holding at 55-60℃ for 30 minutes), and the surface is printed with biodegradable markings, material codes and recycling markings; S32. Closed-loop recycling: The process is carried out in the following steps: crushing and screening, conveying and scanning, intelligent sorting, purity detection and dual-path recycling.

[0022] Example 2: A PHA food packaging material, made from the following raw materials in parts by weight: 60 parts of medium- and long-chain PHA (a copolymer of polyhydroxyhexanoic acid and polyhydroxyoctanoic acid), 20 parts of carbon dioxide copolymer, 3 parts of KH-550 modified silica, 1 part of plant essential oil antibacterial microcapsules, 1 part of polycaprolactone plasticizing microcapsules, 0.1 parts of food-grade stabilizer, and 0.5 parts of dynamic crosslinking agent.

[0023] The microcapsule parameters and preparation methods were performed exactly as described in Example 1.

[0024] Example 3: A PHA food packaging material, made from the following raw materials in parts by weight: 75 parts of medium- and long-chain PHA (a blend of polyhydroxyhexanoic acid and polyhydroxyoctanoic acid), 30 parts of carbon dioxide copolymer, 8 parts of KH-550 modified silica, 3 parts of plant essential oil antibacterial microcapsules, 2 parts of polycaprolactone plasticizing microcapsules, 0.5 parts of food-grade stabilizer, and 1 part of dynamic crosslinking agent.

[0025] The microcapsule parameters and preparation methods were performed exactly as described in Example 1.

[0026] Example 4: A PHA food packaging material, with the same raw material formula as Example 1, except that: the weight ratio of alginate to chitosan in the wall material of the plant essential oil antibacterial microcapsules is 6:4, and the wall material of the polycaprolactone plasticized microcapsules is whey protein and pectin (weight ratio 5:3).

[0027] Preparation method: Except for the wall material ratio of the microcapsules, the other steps are performed exactly as described in Example 1.

[0028] Comparative Group 1: The PHA food packaging material and its preparation method provided in this embodiment are basically the same as those in Example 1, except that 100 parts of medium- and long-chain PHA (a copolymer of polyhydroxyhexanoic acid and polyhydroxyoctanoic acid) are used, and no other components are used.

[0029] Preparation method: only the microcapsule preparation in the pretreatment and the addition of other components in the premixing are omitted. The remaining molding and post-processing steps are performed in accordance with Example 1.

[0030] Comparative Group 2: The PHA food packaging material and its preparation method provided in this embodiment differ in that the raw material composition is: 70 parts of medium- and long-chain PHA, 25 parts of carbon dioxide copolymer, 25 parts of unmodified SiO2, 0.3 parts of food-grade stabilizer, 0.7 parts of dynamic crosslinking agent, and no microcapsule components.

[0031] Preparation method: Simply replace "KH-550 modified SiO2" with "unmodified SiO2", and perform the remaining steps as in Example 1.

[0032] Comparative Group 3: The PHA food packaging material and its preparation method provided in this embodiment differ in the raw material composition: 70 parts of medium- and long-chain PHA, 25 parts of carbon dioxide copolymer, 25 parts of KH-550 modified SiO2, 2 parts of nano-silver antibacterial agent, 1 part of polycaprolactone plasticizer, 0.3 parts of food-grade stabilizer, and 0.7 parts of dynamic crosslinking agent.

[0033] Preparation method: The microcapsule preparation step is omitted. Nano silver antibacterial agent and polycaprolactone plasticizer are added directly. The remaining steps are performed in accordance with Example 1.

[0034] Comparative Group 4: The PHA food packaging material and its preparation method provided in this embodiment differ in the raw material composition: 70 parts of medium- and long-chain PHA, 5 parts of KH-550 modified SiO2, 2 parts of plant essential oil antibacterial microcapsules, 1 part of polycaprolactone plasticizing microcapsules, 0.3 parts of food-grade stabilizer, and 0.7 parts of dynamic crosslinking agent.

[0035] Preparation method: Follow the steps in Example 1 exactly (without adding carbon dioxide copolymer).

[0036] Comparative Group 5: The PHA food packaging material and its preparation method provided in this embodiment have the same raw material composition as in Example 1, except that the wall material of the plant essential oil antibacterial microcapsules is only alginate, and the wall material of the polycaprolactone plasticized microcapsules is only whey protein.

[0037] Preparation method: Except for the microcapsule wall material being a single component, all other steps were performed exactly as described in Example 1.

[0038] Comparative Group 6: The PHA food packaging material and its preparation method provided in this embodiment have the following raw material composition: 70 parts of medium- and long-chain PHA, 25 parts of carbon dioxide copolymer, 25 parts of KH-550 modified SiO2, 2 parts of plant essential oil antibacterial microcapsules, 1 part of polycaprolactone plasticizing microcapsules, and 0.3 parts of food-grade stabilizer.

[0039] Preparation method: Follow the steps in Example 1 exactly (without adding dynamic crosslinking agent).

[0040] Comparative Group 7: The PHA food packaging material and its preparation method provided in this embodiment have the same raw material composition as in Example 1, but the "closed-loop recycling" step in the preparation method is replaced with: B1. Crushing and screening: Same as in Example 1; B2. Density sorting: The particles are placed in saturated salt water (density 1.18 g / cm³). 3 In this context, floating particles are considered as PHA recycled material; B3. Drying and recycling: Collect floating particles, dry them, and then granulate them directly.

[0041] The remaining steps are the same as in Example 1.

[0042] Test Experiment 1: Thermal and Mechanical Property Testing Referring to the aforementioned standards, the thermal decomposition temperature, long-term service temperature range, tensile strength, elongation at break, and SEM cross-sectional morphology of all groups were tested. The results are shown in Table 1 below: Table 1: Test Data Record Table for Complete Test Results of Thermal and Mechanical Properties

[0043] This experiment adopted the national standard method. The thermogravimetric analyzer (TGA) was used to test the thermal decomposition temperature according to GB / T30293-2013. The universal testing machine was used to test the tensile strength and elongation at break according to the GB / T1040 series standards. The cross-sectional morphology was observed using a scanning electron microscope (SEM).

[0044] Test Experiment 1 analysis shows that, compared to control group 1, which is a pure medium-to-long-chain PHA matrix (without other composite components), its thermal decomposition temperature is only 235℃, its long-term service temperature range is limited to -5 to 60℃, its tensile strength is 28.5 MPa, its elongation at break is 12.3%, and its SEM cross-section shows obvious molecular chain fracture grooves, indicating extremely poor compatibility. This result fully demonstrates that a single PHA matrix has inherent defects such as insufficient thermal stability and poor toughness due to its simple molecular chain structure and lack of interfacial synergy. The synergistic effect of components such as carbon dioxide copolymer, KH-550 modified SiO2, and microcapsules in the composite system of this invention is the core to make up for this defect—carbon dioxide copolymer improves crystallization stability, modified SiO2 strengthens interfacial bonding, and microcapsules optimize functional adaptation, together forming the basis for performance improvement.

[0045] Comparative group 2, using unmodified SiO2 instead of KH-550 modified SiO2, exhibited significantly lower thermal decomposition temperature (262℃), tensile strength (35.2 MPa), and elongation at break (18.6%) compared to the example groups. Furthermore, SEM analysis revealed SiO2 particle agglomeration, with noticeable gaps between the particles and the PHA matrix. The core reason for this difference lies in the lack of active groups on the surface of unmodified SiO2 capable of forming chemical bonds with PHA carboxyl groups and carbon dioxide copolymer ester groups. This results in weak interfacial bonding between the inorganic filler and the organic matrix, hindering effective stress transfer. The agglomerated particles also become internal defects, leading to performance degradation under temperature changes or stress. In contrast, the KH-550 modified SiO2 in the example groups demonstrated significantly improved interfacial compatibility due to the introduction of stable chemical bonds between the amino groups introduced by surface silanization treatment. This validates the necessity of KH-550 modification for strengthening interfacial bonding and enhancing the overall material performance.

[0046] Compared to group 4, which did not contain the carbon dioxide copolymer, the thermal decomposition temperature dropped to 258℃, the long-term service temperature range narrowed to -8 to 70℃, the tensile strength was 33.6 MPa, the elongation at break was 16.8%, and a small amount of phase separation gaps appeared in the SEM cross-section. This is because the ester groups in the carbon dioxide copolymer molecular structure have good structural compatibility with PHA, which can fill the gaps between PHA molecular chains and inhibit molecular chain aggregation, thereby improving the crystallization stability of PHA and reducing the risk of phase separation. Without this copolymer, the polarity difference between PHA and other components cannot be alleviated, and the microscopic phase separation phenomenon is obvious, resulting in a significant decline in thermal stability and mechanical properties. This fully demonstrates the core value of carbon dioxide copolymer in improving system compatibility and enhancing thermal stability and mechanical properties.

[0047] Examples 1-4 cover the upper and lower limits of the formulation by weight (Example 2 is the lower limit of the formulation, Example 3 is the upper limit of the formulation) and the process optimization scenario (Example 4 adjusts the proportion of microcapsule wall material). Their thermal decomposition temperatures all reach above 280℃ (Example 2 is 281℃, Example 3 is 292℃, Example 4 is 286℃), the long-term service temperature range covers -18 to 92℃, the tensile strength is ≥39.2MPa, the elongation at break is ≥25.3%, and the SEM cross-sections all show a dense and uniform morphology without obvious gaps or agglomeration. The performance data of Examples 2 (lower limit of formulation) and 3 (upper limit of formulation) both meet the core requirements of food packaging for thermal stability and mechanical properties, proving that the raw material weight range (60-75 parts of medium- and long-chain PHA, 20-30 parts of carbon dioxide copolymer, etc.) defined in this invention is scientifically reasonable, and both the upper and lower limit formulations can achieve the expected technical effects. Example 4 adjusted the proportion of microcapsule wall materials (antibacterial microcapsules alginate and chitosan 6:4, plasticized microcapsules whey protein and pectin 5:3), and its performance was basically the same as that of Example 1 (basic formulation), indicating that the core role of microcapsule composite wall materials is "combined synergistic barrier" rather than a single fixed proportion, further verifying the flexibility of the technical solution in process implementation, which can adapt to the parameter fine-tuning needs under different production scenarios, and provides a wider range of adaptability for industrial applications.

[0048] Test Experiment 2: Migration and Heavy Metal Content Detection Experiment. The migration amount and heavy metal content of antibacterial agents / plasticizers in all groups were tested. The results are shown in Table 2 below: Table 2: Record of Complete Detection Results of Migration Amount and Heavy Metal Content Test Data

[0049] This experiment, based on national standard methods, mainly employs food simulant immersion migration test (refer to GB31604.1-2015, etc.) combined with high performance liquid chromatography to detect specific migrating substances, and uses inductively coupled plasma mass spectrometry (refer to GB31604.49-2016, etc.) to detect heavy metal content in order to assess food safety risks.

[0050] Test Experiment 2 analysis shows that, in control group 3, which used nano-silver as an antibacterial agent and did not encapsulate the plasticizer, the silver ion content reached 8.2 mg / kg, far exceeding the heavy metal limit standard for food contact materials. The polycaprolactone migration was also as high as 15.6 mg / kg, indicating a significant risk of heavy metal accumulation and active ingredient migration. In contrast, the example groups used plant essential oil antibacterial microcapsules instead of nano-silver, and no heavy metals were detected, completely avoiding the heavy metal hazard at the source. Furthermore, the natural properties of plant essential oils improved food contact safety, verifying the scientific rationale behind this alternative.

[0051] In control group 5, microcapsules prepared using single wall materials (alginate and whey protein) showed significantly higher migration rates of gingerol (3.2 mg / kg) and polycaprolactone (8.7 mg / kg) compared to the control group (0.8-1.2 mg / kg and 2.1-3.5 mg / kg, respectively). This is because the single wall material lacks sufficient structural density to form an effective barrier. In contrast, the composite wall materials in control group (alginate + chitosan and whey protein + pectin) formed a more stable coating layer through the synergistic effect of different polymers, effectively delaying the migration of functional components. This demonstrates that composite wall materials are key to controlling migration levels.

[0052] The migration levels of antimicrobial agents and plasticizers, as well as the heavy metal indicators, in all example groups strictly complied with the requirements of the national standard GB4806.7-2016 "Plastic Materials and Products for Food Contact". This fully demonstrates that this technology, through the dual design of "plant essential oil microcapsules replacing heavy metal antimicrobial agents" and "composite wall material coating to control migration", not only solves the safety hazards of traditional solutions but also ensures food contact safety, fully meeting the stringent requirements of food packaging.

[0053] Test Experiment 3: Antibacterial performance and durability test. The antibacterial rate was tested initially and after 10 soakings. The results are shown in Table 3 below: Table 3: Test Data Recording Table for Antibacterial Performance and Durability Integrity Test Results

[0054] This experiment, based on national standard methods, mainly used the film application method (refer to GB / T31402-2015) to quantitatively test the antibacterial rate against Escherichia coli and Staphylococcus aureus, and evaluated the antibacterial durability through simulated immersion treatment.

[0055] Test Experiment 3 analysis shows that, compared to control group 1 which only contained pure PHA matrix and control group 2 which did not add any antibacterial components, both had an initial inhibition rate of 0 against Escherichia coli and Staphylococcus aureus, and showed no antibacterial effect after soaking. This result clearly demonstrates that the realization of antibacterial function depends entirely on the addition of specific antibacterial components. The plant essential oil antibacterial microcapsules in this invention are the core carriers that provide antibacterial activity. Without this component, the antibacterial effect required for food packaging cannot be achieved, directly confirming the indispensability of antibacterial microcapsules in realizing the function.

[0056] In control group 5, antibacterial microcapsules were prepared using a single wall material. Although the initial antibacterial rate was similar to that of the example group (93.2%, 94.0%), after 10 immersions, the antibacterial rate dropped below 78%, indicating a significant decrease in antibacterial effect. This is because the single wall material lacks structural stability and sustained-release regulation capabilities, making it prone to structural damage during repeated contact with the simulated liquid, leading to the rapid release and loss of the core material (ginger essential oil). In contrast, the example group used a composite wall material of "alginate + chitosan." Through the electrostatic attraction and structural complementarity of the two polymer materials, a more stable encapsulation network was formed, enabling the slow release of antibacterial components. Even after 10 immersions, the antibacterial rate remained above 88%, fully demonstrating that the composite wall material design can effectively extend the sustained-release period of antibacterial components and ensure the long-term antibacterial performance of the material during long-term use.

[0057] The initial inhibition rates of the example group against Escherichia coli and Staphylococcus aureus reached 93.8%-95.0% and 94.5%-95.3%, respectively, which were basically the same as those of the control group 3 (95.8% and 96.2%) using nano-silver antibacterial agents. This indicates that the immediate antibacterial effect of the plant essential oil microcapsules is comparable to that of traditional heavy metal antibacterial agents, fully meeting the core requirements of food preservation. More importantly, after 10 immersions, the inhibition rate of the control group 3 decreased to 82.5%-83.1%, while that of the example group remained above 88%, demonstrating superior durability. This difference stems from the slow-release effect of the composite wall material, allowing the plant essential oils to continuously exert their antibacterial activity. In contrast, nano-silver, lacking protective coating, is prone to migration and loss during contact, leading to a rapid decline in its antibacterial effect. In summary, the experimental data fully verify that the plant essential oil microcapsules not only possess antibacterial effects comparable to nano-silver but also have advantages in long-term stability, without the risk of heavy metal contamination, making them suitable for long-term use in food packaging.

[0058] Test Experiment 4: Recycling performance test experiment, which tested the performance retention rate, degradation rate and initial purity of recycled material after 3 recycling cycles. The results are shown in Table 4 below: Table 4: Test Data Record Table of Complete Recycling Performance Test Results

[0059] This experiment follows national standard methods, primarily employing standard tensile testing (referring to GB / T 1040 series) to assess the retention rate of mechanical properties after recycling, biodegradation rate testing under composting conditions (referring to GB / T 19277.1-2011) to assess the degradation rate, and the purity of the recycled material to be assessed in accordance with the recycling plastics characterization standard (GB / T 40006.5-2021).

[0060] Test Experiment 4 analysis shows that, in comparison group 6, which did not add a dynamic crosslinking agent, the tensile strength retention rate after three recycling cycles was only 70.1%, significantly lower than the retention rate of over 81% in the other example groups, indicating a significant decline in mechanical properties. The core reason is that, without a dynamic crosslinking agent, the crosslinking bonds formed during the material's use and recycling granulation process are irreversible. Repeated heating and melting lead to molecular chain breakage and crosslinking network damage, resulting in a continuous decline in mechanical properties. In contrast, the dynamic crosslinking agent (lipoic acid amide analog) used in this invention has the characteristics of "stable crosslinking during use and reversible depolymerization during recycling." It can ensure the strength of the material during use while avoiding irreversible damage to the molecular chains during recycling, effectively maintaining the performance stability of the recycled material. This fully demonstrates that the reversible crosslinking design of the dynamic crosslinking agent is the core of ensuring recycling performance.

[0061] The control group 7, using traditional density sorting, had an initial purity of only 89.6%, far lower than the over 98% purity of the example group. Furthermore, the corresponding tensile strength retention rate (74.1%) was also lower than that of the example group. This is because traditional density sorting relies solely on differences in material density, making it difficult to distinguish PHA from other plastics with similar densities (such as PLA). This results in impurities being mixed into the recycled material, which can become structural defects and reduce the mechanical properties of the recycled material. In contrast, the example group employed a "multispectral imaging + machine learning" intelligent sorting technology, which can accurately capture the characteristic absorption peaks of PHA in specific wavelength bands, achieving 360° seamless identification and separation. This significantly improves the purity of the recycled material, thereby ensuring recycling performance and verifying the significant superiority of this intelligent sorting technology compared to traditional methods.

[0062] After three recycling cycles, all example groups maintained a degradation rate of over 84.9% after 60 days, essentially matching the degradation performance of materials that were not recycled multiple times. This result demonstrates that the closed-loop recycling system of this invention only regenerates and regulates the material's morphology and structure, without altering the inherent molecular structure and biodegradability of PHA and its composite components. This achieves both efficient resource recycling and preserves the material's full biodegradability, completely solving the problem of balancing traditional recycling technologies with degradation performance, highlighting the environmental integrity and practicality of the technical solution.

[0063] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A PHA food packaging material, characterized in that, It is made from the following raw materials in parts by weight: 60-75 parts of medium- and long-chain PHA, 20-30 parts of carbon dioxide copolymer, 3-8 parts of KH-550 modified silica, 1-3 parts of plant essential oil antibacterial microcapsules, 1-2 parts of polycaprolactone plasticized microcapsules, 0.1-0.5 parts of food-grade stabilizer, and 0.5-1 parts of dynamic crosslinking agent.

2. The PHA food packaging material according to claim 1, characterized in that, The medium- and long-chain PHA is a copolymer or blend of polyhydroxyhexanoic acid and polyhydroxyoctanoic acid, and the carbon dioxide copolymer is a composite system of polypropylene carbonate and polypropylene carbonate-ethylene oxide composite copolymer.

3. The PHA food packaging material according to claim 1, characterized in that, The wall material of the plant essential oil antibacterial microcapsules is a mixture of alginate and chitosan, with a weight ratio of alginate to chitosan of 7:

5. The core material is ginger essential oil. The encapsulation rate of the plant essential oil antibacterial microcapsules is not less than 90%, and the particle size is 10-50 micrometers.

4. The PHA food packaging material according to claim 1, characterized in that, The wall material of the polycaprolactone plasticized microcapsules is a mixture of whey protein and pectin, with an encapsulation rate of not less than 85%.

5. The PHA food packaging material according to claim 1, characterized in that, The dynamic crosslinking agent is a thioctin analogue, and the food-grade stabilizer is a food contact grade additive that can delay the oxidative degradation of PHA.

6. A method for manufacturing any one of the PHA food packaging materials described in 1-5, characterized in that, Includes the following steps: S1. Pretreatment: including modified silica preparation, microcapsule preparation and PHA purification; S11. Preparation of modified silica: Add silica powder to anhydrous ethanol and ultrasonically disperse for 30 minutes to form a suspension; add KH-550 (3% by mass of silica) to the suspension, and stir at 70℃ for 6 hours at a stirring rate of 200-300 rpm; after the reaction, centrifuge at 3000-4000 rpm for 10 minutes to separate the solid particles, wash with anhydrous ethanol 3-4 times until no amino groups are detected in the supernatant, and dry at 80℃ and -0.08 to -0.09 MPa for 12 hours until the water content is not higher than 0.5% to obtain KH-550 modified silica; S12. Microcapsule preparation: Plant essential oil antibacterial microcapsules and polycaprolactone plasticized microcapsules were prepared by a composite coagulation method. Among them, the plant essential oil antibacterial microcapsules were mixed with the wall material and the core material at a weight ratio of 3:1 and the pH value was adjusted to 4.0-4.

5. The polycaprolactone plasticized microcapsules were prepared by the same composite coagulation method. S13, PHA Refining: The PHA obtained from fermentation is broken down, concentrated by centrifugation, and then vacuum dried until the moisture content is no higher than 0.5%; S2, Blending Molding: including premixing, melt blending and molding processing; S21. Premixing: Add medium- and long-chain PHA, carbon dioxide copolymer, KH-550 modified silica, food-grade stabilizer and dynamic crosslinking agent into a high-speed mixer and stir at 100-110℃ for 15 minutes at a speed of 300-400 rpm. S22. Melt blending: Add the premix to a twin-screw extruder, set the gradient temperature zone 1 to 145-155℃, zone 2 to 160-170℃, and zone 3 to 170-180℃, and the screw speed to 280-320 rpm. Add plant essential oil antibacterial microcapsules and polycaprolactone plasticizing microcapsules, and extrude and granulate. S23. Molding process: Add the granules to an injection molding machine or blow molding machine for molding. The injection temperature is 165-175℃, the blow molding air pressure is 0.6-0.8 MPa, and the cooling time is 15-20 seconds. S3. Post-processing and closed-loop recycling: S31. Post-processing: The molded products are subjected to medium-wave infrared annealing, with a heating rate of 3-5℃ per minute and a holding time of 55-60℃ for 30 minutes. The surface is printed with biodegradable markings, material codes and recycling markings. S32, Closed-loop recycling: Includes crushing and screening, conveying and scanning, intelligent sorting, purity detection and dual-path recycling steps.

7. The preparation method according to claim 6, characterized in that, The preparation of plant essential oil antibacterial microcapsules in step S12 also includes the following specific steps: A1. Raw material dissolution and core material emulsification: Alginate is added to deionized water to prepare a 1.5% to 2.0% aqueous solution, and chitosan is added to a 1% dilute acetic acid aqueous solution to prepare a 1.0% to 1.5% aqueous solution; ginger essential oil is added to the alginate aqueous solution, and the mixture is homogenized at high speed for 15-20 minutes or ultrasonically emulsified to disperse it into droplets of 1-5 micrometers. A2. Coagulation: Add the chitosan aqueous solution dropwise to the emulsion at a rate of 1-2 ml per minute, stir at 300-400 rpm and adjust the pH to 4.0-4.5; A3. Curing: Add 1.0% to 2.0% calcium chloride solution, the amount of which is 5% to 8% of the total mass of the wall material. Stir and react for 30 minutes, then let it stand and age for 1 hour. A4. Separation and drying: Centrifuge at 3000 rpm for 10 minutes, wash the precipitate 3 times with deionized water, and dry at 60℃ and -0.08 MPa for 8 hours until the moisture content is no higher than 1%.

8. The preparation method according to claim 6, characterized in that, In step S22, the plant essential oil antibacterial microcapsules and polycaprolactone plasticized microcapsules are added through the side feed port of the second zone of the twin-screw extruder.

9. The preparation method according to claim 6, characterized in that, The specific steps of closed-loop recycling in step S32 are as follows: B1. Crushing and Screening: The recycled PHA packaging material is crushed into particles of 5-20 mm and passed through a 10-mesh sieve to remove large impurities. B2. Conveying and Scanning: The crushed material is conveyed at a constant speed by a belt conveyor, and the multispectral imaging system above scans each particle 360°, simultaneously collecting spectral data and location information. B3. Intelligent Judgment and Sorting: The machine learning model analyzes spectral data in real time and marks the position of PHA particles. When the particles reach the sorting area, the high-pressure air jet device accurately blows out the PHA particles, which fall into a dedicated recycling bin. The waste continues to be transported to the ordinary waste bin. B4. Purity Detection and Feedback: A secondary spectral detection is set at the outlet of the recycling bin. If the purity does not reach 98%, the system automatically adjusts the spectral recognition threshold to optimize the sorting accuracy. B5. Dual-path recycling: Recyclable particles without obvious aging are directly subjected to physical recycling and granulation; Severely aged waste materials are put into the recycling reactor, and 5% of ethylene glycol by mass is added as a depolymerizing agent at 180-200℃ and 0.3-0.5 MPa. After depolymerization for 4 hours, regeneration polymerization is carried out at 160-170℃ under a nitrogen atmosphere.

10. The preparation method according to claim 9, characterized in that, In step B2, the multispectral imaging system includes a visible light camera, a near-infrared camera, and a mid-infrared camera, which acquires characteristic absorption peak data of PHA in the near-infrared band (1.70-1.76 μm) and the mid-infrared band (5.7-5.9 μm). In step B3, the machine learning model is established based on the characteristic spectrum of PHA.

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