A bio-based high-barrier degradable packaging material and a method for preparing the same

Abstract

This invention discloses a bio-based high-barrier biodegradable packaging material and its preparation method, belonging to the field of polymer materials technology. The material comprises the following formulation: polylactic acid, polybutylene adipate / terephthalate, starch, nano-clay, polyvinyl alcohol, glycerin, plant wax, compatibilizer, antioxidant, and lubricant. This invention introduces nanofillers, polyvinyl alcohol, and plant wax into a continuous phase system composed of polylactic acid and flexible biodegradable polyester to construct a multi-level synergistic structure. Simultaneously, a compatibilizer is used to regulate the interfacial bonding state of the multiphase components, enabling each component to form a stable and continuous structural distribution at the microscale. This effectively extends the gas diffusion path, reduces the water vapor permeation rate, and balances the mechanical properties and processing stability of the material without introducing complex functionalized components, thus comprehensively improving the overall barrier performance and practical application adaptability of the bio-based packaging material.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a bio-based high-barrier biodegradable packaging material and its preparation method. Background Technology

[0002] With the continued growth in demand for green packaging and environmentally friendly materials, bio-based biodegradable materials, such as polylactic acid (PLA) and starch, are widely used in food packaging, daily necessities packaging, and other fields. However, existing bio-based biodegradable packaging materials generally suffer from insufficient barrier properties, especially in terms of oxygen and water vapor barrier properties, which fail to meet the needs of mid-to-high-end packaging. On the one hand, the molecular chain arrangement of bio-based polyester materials such as PLA is relatively loose, resulting in a short gas diffusion path and high oxygen permeability. On the other hand, hydrophilic components such as starch easily absorb moisture and expand in the material system, further weakening the material's water vapor barrier properties. Meanwhile, existing technologies often improve barrier properties by simply adding inorganic fillers or high-barrier components, but due to poor compatibility between components, significant phase separation structures are easily formed, leading to increased interface defects. This not only limits the improvement in barrier properties but may also cause a decline in mechanical properties. Furthermore, some technical solutions rely excessively on complex modified materials or special functional additives, resulting in complex composition systems, narrow processing windows, and difficulties in industrial-scale promotion. Therefore, how to achieve synergistic improvement in gas and water vapor barrier performance by rationally constructing multiphase structures and barrier pathways while ensuring the biodegradability and processing adaptability of materials has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a bio-based high-barrier biodegradable packaging material and its preparation method, thereby solving the problems mentioned in the background section.

[0004] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a bio-based high-barrier biodegradable packaging material, which comprises the following formulation by weight parts: Polylactic acid 60-90 parts; 20-50 parts of poly(butylene adipate / terephthalate); 10-30 parts starch; 2-8 parts of nano-clay; 5-20 parts of polyvinyl alcohol; 3-10 parts glycerin; 1-5 parts of plant wax; 2-6 parts compatibilizer; Antioxidant 0.3 to 1 part; Lubricant 0.5 to 2 parts.

[0005] To further optimize this technical solution, the nano-clay is an organically modified layered silicate with an interlayer spacing controlled within the range of 1.5 to 3.5 nm, and exists in the packaging material in a composite dispersion structure of exfoliated and intercalated states, wherein the mass proportion of the exfoliated state is 30% to 70%.

[0006] To further optimize this technical solution, the degree of alcoholysis of the polyvinyl alcohol is 85%–99%, and the number-average molecular weight is 2 × 10⁻⁶. 4 ~8×10 4 It is distributed in the packaging material in the form of a continuous or semi-continuous phase and forms a hydrogen bond network structure with starch.

[0007] To further optimize this technical solution, the starch is a pre-plasticized or esterified starch with a particle size of 5-30 μm and a crystallinity of 10%-35%, and forms a transition interface structure between the dispersed phase and the continuous phase in the material; The starch surface contains hydroxyl or ester functional groups, which form a stable interfacial bonding layer with polyvinyl alcohol and compatibilizer.

[0008] To further optimize this technical solution, the compatibilizer is maleic anhydride-grafted polyester or grafted polyolefin, with a grafting rate of 0.5% to 3.0% and a number-average molecular weight of 1×10⁻⁶. 4 ~5×10 4 ; The compatibilizer is distributed at the interfaces of each phase in the material, forming an interfacial transition layer with a thickness of 20-100 nm.

[0009] To further optimize this technical solution, the plant wax is a natural wax substance with a melting point in the range of 60 to 90°C. During the material forming process, it undergoes phase separation and migrates to the surface of the material to form a continuous hydrophobic layer with a thickness of 1 to 10 μm.

[0010] To further optimize this technical solution, the glycerol exists in a molecularly dispersed state in the packaging material, and its glass transition temperature is adjusted by forming hydrogen bonds with polyvinyl alcohol and starch, thereby reducing the glass transition temperature to the range of 30-60°C.

[0011] To further optimize this technical solution, the polylactic acid and poly(butylene adipate) / poly(terephthalate) form an "island structure" or a "bicontinuous structure" in the packaging material, wherein the volume fraction of the flexible phase is 20% to 40%.

[0012] To further optimize this technical solution, the lubricant is a fatty acid or its metal salt, with a melting point of 50-120°C, which forms an interfacial lubrication layer during the packaging material processing, and the thickness of the interfacial lubrication layer is 10-50 nm.

[0013] A method for preparing a bio-based high-barrier degradable packaging material, based on the above-mentioned bio-based high-barrier degradable packaging material, includes the following steps: S1. Pre-disperse the nano-clay and construct an initial barrier precursor system; S2. Pre-plasticize starch to form a transition phase component that matches the barrier precursor system; S3. Perform premixing of the main matrix to form a main matrix premix that can support the barrier structure; S4. The barrier precursor system, starch transition phase component and main matrix premix are melt-blended and extruded to construct a multi-phase synergistic high barrier biodegradable material masterbatch. S5. Introduce plant wax into the molding stage and perform secondary heat treatment to form a hydrophobic barrier layer on the surface of the material. S6. Perform shaping and post-treatment on the molded material to stabilize the internal barrier structure and the surface hydrophobic structure.

[0014] Compared with the prior art, the present invention provides a bio-based high-barrier biodegradable packaging material and its preparation method, which has the following beneficial effects: This bio-based high-barrier biodegradable packaging material and its preparation method introduce layered nanofillers, polyvinyl alcohol forming a hydrogen bond network with starch, and plant waxes that can migrate to the surface during molding into a continuous phase system composed of polylactic acid and flexible biodegradable polyester. This constructs a multi-layered synergistic structure of "internal tortuous barrier path - intermediate dense barrier region - surface hydrophobic barrier". At the same time, a compatibilizer is used to regulate the bonding state of the multiphase interface, so that each component forms a stable and continuous structural distribution at the microscale. Thus, without introducing complex functionalized components, it effectively extends the gas diffusion path, reduces the water vapor permeation rate, and takes into account the mechanical properties and processing stability of the material, thereby improving the overall barrier performance and practical application adaptability of the bio-based packaging material. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic flowchart of a method for preparing a bio-based high-barrier biodegradable packaging material proposed in this invention. Detailed Implementation

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0018] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0019] Secondly, the term "an embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places throughout this specification does not necessarily refer to the same embodiment, nor is it a single embodiment or an embodiment selectively excluded from other embodiments.

[0020] A bio-based high-barrier biodegradable packaging material, comprising the following formulation by weight parts: Polylactic acid (PLA) 60-90 parts; as the main skeleton material, it provides basic mechanical strength and film-forming properties, while also having good biodegradability, and is the main structural source of this system.

[0021] Polybutylene adipate / terephthalate (PBAT) 20-50 parts; used to improve the brittleness of PLA, enhance the material's flexibility and impact resistance, while maintaining its overall biodegradability, making the material more suitable for packaging applications.

[0022] Starch 10-30 parts; as a natural bio-based filler, it reduces costs on the one hand, increases the degradation rate of materials on the other hand, and forms a multiphase structure, which is beneficial for extending the barrier pathway.

[0023] Nano-clay 2-8 parts; belonging to layered structure filler, it forms a "maze-like barrier path" inside the material, which significantly improves the oxygen and water vapor barrier performance and is a key component for achieving high barrier performance.

[0024] Polyvinyl alcohol (PVA) 5-20 parts; provides excellent gas barrier properties (especially oxygen barrier), while having good compatibility with starch and can form a continuous barrier phase.

[0025] Glycerin 3-10 parts; as a plasticizer, it improves the flexibility of the system, reduces the processing temperature, and prevents the material from becoming brittle.

[0026] 1-5 parts of plant wax; used to improve the hydrophobic properties of materials, enhance water vapor barrier ability, and improve surface properties, making the materials more suitable for packaging applications.

[0027] 2-6 parts compatibilizer; enhances the interfacial bonding between PLA, PBAT, starch and PVA, reduces phase separation, and improves overall mechanical properties and barrier stability.

[0028] Antioxidant 0.3 to 1 part; to prevent thermal and oxidative degradation of materials during processing and to ensure molecular chain stability.

[0029] Lubricant 0.5 to 2 parts; improves melt flow properties, reduces processing energy consumption, and enhances extrusion and molding stability.

[0030] The nano-clay is an organically modified layered silicate with an interlayer spacing controlled within the range of 1.5–3.5 nm. It exists in the packaging material in a composite dispersion structure of exfoliated and intercalated states, with the exfoliated state accounting for 30%–70% of the mass. During melt blending, the nano-clay forms an oriented arrangement along the extrusion direction with an orientation factor of not less than 0.6, thereby constructing a continuous and tortuous gas diffusion path structure within the material to effectively block oxygen and water vapor.

[0031] The degree of alcoholysis of the polyvinyl alcohol is 85%–99%, and the number average molecular weight is 2 × 10⁻⁶. 4 ~8×10 4 It is distributed in the packaging material in the form of a continuous or semi-continuous phase and forms a hydrogen bond network structure with starch, so that the two form a dense barrier layer region in the molten state. The volume fraction of the barrier layer region is 15% to 35%, thereby improving the overall gas barrier performance of the material.

[0032] The starch is a pre-plasticized or esterified starch with a particle size of 5–30 μm and a crystallinity of 10%–35%, forming a transitional interface structure between the dispersed and continuous phases in the material. The starch surface contains hydroxyl or ester functional groups, forming a stable interfacial bonding layer with polyvinyl alcohol and a compatibilizer. The thickness of this interfacial layer is 50–200 nm, thereby improving the structural stability of the multiphase system and extending the gas diffusion path.

[0033] The compatibilizer is maleic anhydride-grafted polyester or grafted polyolefin, with a grafting rate of 0.5% to 3.0% and a number-average molecular weight of 1×10⁻⁶. 4 ~5×10 4 The compatibilizer is distributed at the interfaces of each phase in the material, forming an interfacial transition layer with a thickness of 20–100 nm. It enhances the interfacial bonding strength between polylactic acid, polybutylene adipate / terephthalate, and starch through chemical bonding or polar interaction, increasing the interfacial peel strength to the range of 5–15 MPa, thereby improving the overall mechanical properties and barrier stability of the material.

[0034] The plant wax is a natural wax substance with a melting point in the range of 60-90℃. During the material molding process, it undergoes phase separation and migrates to the surface of the material to form a continuous hydrophobic layer with a thickness of 1-10μm. The contact angle of the hydrophobic layer is not less than 90° and the coverage reaches more than 80%, thereby significantly reducing the adsorption and penetration of water vapor on the material surface and improving the water vapor barrier performance.

[0035] The glycerol exists in a molecularly dispersed state in the packaging material. By forming hydrogen bonds with polyvinyl alcohol and starch, its glass transition temperature is adjusted to a range of 30-60°C, thereby maintaining the stability of the barrier structure while ensuring flexibility.

[0036] The polylactic acid and poly(butylene adipate) terephthalate form an "island structure" or "bicontinuous structure" in the packaging material, wherein the volume fraction of the flexible phase is 20% to 40%. By controlling the phase structure morphology of the two, the material maintains high strength while possessing excellent impact resistance and avoids the decline in barrier properties caused by phase separation.

[0037] The lubricant is a fatty acid or its metal salt, with a melting point of 50–120°C. During the processing of the packaging material, it forms an interfacial lubrication layer with a thickness of 10–50 nm. This reduces the melt viscosity and improves the dispersion uniformity of the nano-clay and starch, resulting in a denser and more stable internal structure of the material.

[0038] Reference Figure 1 A method for preparing a bio-based high-barrier degradable packaging material, based on the above-mentioned bio-based high-barrier degradable packaging material, includes the following steps: S1. Pre-disperse the nano-clay and construct an initial barrier precursor system.

[0039] First, the nano-clay is dried at 80–100℃ for 4–8 hours to control its moisture content below 1.0%, thus preventing polylactic acid degradation or clay agglomeration due to residual moisture during subsequent melt blending. The dried nano-clay is then premixed with polyvinyl alcohol (PVA) in a high-speed mixer. Preferably, the PVA is first pulverized to 40–100 mesh to improve the uniformity of contact between it and the nano-clay. During premixing, the speed is controlled at 500–1200 r / min, and the time is controlled at 10–25 min, allowing some nano-clay sheets to adsorb onto the surface of the PVA particles and form an initial coating. The polarity of PVA provides initial conditions for the subsequent intercalation and dispersion of clay sheets in the matrix, making it easier for the nano-clay to form a dispersion structure with both exfoliated and intercalated states in the melt shear field.

[0040] S2. The starch is pre-plasticized to form a transition phase component that matches the barrier precursor system.

[0041] Building upon S1, to prevent localized carbonization, coarse particle aggregation, or interfacial debinding of starch after it directly enters the main melt, separate pretreatment of the starch is necessary. Specifically, the starch is dried at 70–90°C for 2–6 hours, controlling its moisture content to 2%–8%. Then, it is added to a mixing device with glycerol in a predetermined ratio for pre-plasticization mixing. The mixing temperature is controlled at 60–90°C, and the mixing time is controlled at 15–40 minutes, ensuring that the glycerol uniformly penetrates the starch particles to form a plasticized starch intermediate. If modified starch is used, the particle size should be maintained within the range of 5–30 μm to facilitate the formation of a stable interfacial transition structure in the continuous phase composed of polylactic acid and PBAT. After this step, the starch no longer exists as a simple rigid filler but possesses certain thermoplastic processing adaptability. It can form a dense barrier region with polyvinyl alcohol during subsequent blending and construct a multiphase interfacial layer with the compatibilizer, thereby reducing brittle defects and improving the continuity of the barrier path.

[0042] S3. Perform premixing of the main matrix to form a main matrix premix that can support the barrier structure.

[0043] After the barrier precursor system is formed in S1 and the starch transition phase component is formed in S2, a stable main continuous phase needs to be constructed to support the aforementioned barrier and transition phases. Specifically, polylactic acid (PLA) and PBAT are dried separately, with PLA preferably dried under vacuum at 50–70°C for 4–8 hours and PBAT preferably dried at 60–80°C for 3–6 hours to avoid hydrolytic degradation during processing. The dried PLA, PBAT, compatibilizer, antioxidant, and lubricant are then added to a high-speed mixer and mixed for 5–20 minutes. The mixing temperature can be controlled between room temperature and 60°C to avoid premature softening and clumping. In this step, the compatibilizer is preferably pre-contacted with PBAT so that it preferentially resides at the interface between different resin phases and starch phases during subsequent melting, thereby improving the interfacial bonding strength; the antioxidant is used to inhibit the thermo-oxidative degradation of polyester components under high-temperature shear; and the lubricant is used to adjust the conveying state and dispersion uniformity of the material in the twin-screw extruder.

[0044] S4. The barrier precursor system, starch transition phase component and main matrix premix are melt-blended and extruded to construct a multiphase synergistic high barrier biodegradable material masterbatch.

[0045] After forming the main matrix premix capable of supporting the barrier structure in S3, the barrier precursor system obtained in S1, the starch transition phase component obtained in S2, and the main matrix premix obtained in S3 are added to a twin-screw extruder for melt blending. The extruder temperature zones are preferably controlled within the range of 130–190°C, the screw speed is controlled within 150–400 r / min, and the average residence time of the material in the barrel is controlled within 30–120 s. In this step, the initial temperature zone focuses on the melt plasticization of polylactic acid and PBAT, the middle temperature zone focuses on the dispersion and embedding of starch and polyvinyl alcohol, and the final temperature zone focuses on using the shear field to induce intercalation and exfoliation of the nano-clay sheets and their orientation along the melt flow direction. During this stage, the compatibilizer gradually migrates to the interfaces between the phases, forming an interfacial transition layer and reducing the degree of phase separation between the polylactic acid / PBAT phase and the starch / PVA phase. By controlling shear strength and temperature distribution, nano-clay can form tortuous diffusion paths within the material, creating continuous or semi-continuous barrier regions between polyvinyl alcohol and starch, while maintaining the toughness and processability of the main material. The extruded melt is then cooled and pelletized to obtain a high-barrier, biodegradable packaging material masterbatch.

[0046] S5. Introduce plant wax into the molding stage and perform secondary heat treatment to form a hydrophobic barrier layer on the surface of the material.

[0047] Building upon the internal barrier network and multiphase stable structure already formed in S4, to further enhance water vapor barrier performance, plant wax is introduced during subsequent film or sheet forming stages, or it is directionally migrated within the masterbatch during the forming process. Specifically, plant wax can be premixed with the masterbatch obtained from S4 and then processed by casting, blown film, or sheeting; alternatively, plant wax can be formulated as a low-melting-point auxiliary component and added at the rear of the forming machine's feed section. The forming temperature is preferably controlled within the range of 140–185°C, and the draw ratio or stretch ratio is adjusted according to the product type to preferentially enrich the plant wax on the melt surface and form a continuous or quasi-continuous hydrophobic layer during cooling and solidification. The spatial distribution of the plant wax is controlled by the forming thermal history and flow field to concentrate it as much as possible on the material surface, reducing the permeation rate of water after adsorption on the surface. If a film preparation method is used, the film thickness is preferably controlled within the range of 20–150 μm to balance barrier performance, flexibility, and forming stability.

[0048] S6. Perform shaping and post-treatment on the molded material to stabilize the internal barrier structure and the surface hydrophobic structure.

[0049] After the material is formed in step S5, a heat-setting process is required to prevent the internal multiphase structure from continuing to relax after cooling and affecting the barrier performance. Specifically, the formed material is heat-set at 50–80°C for 1–12 hours to moderately increase the crystallinity of polylactic acid and stabilize the polyvinyl alcohol / starch barrier region and the nano-clay orientation structure. Simultaneously, the surface plant wax undergoes limited rearrangement within this temperature range, which is beneficial for forming a more uniform hydrophobic surface. If necessary, a constant temperature and humidity conditioning treatment can be further performed, preferably at a temperature of 20–30°C, a relative humidity of 40%–60%, and a time of 12–48 hours, to release internal stress and stabilize dimensions. After this step, the resulting packaging material forms a tortuous barrier path composed of nano-clay sheets inside, a dense barrier region composed of polyvinyl alcohol and starch in the middle, and a hydrophobic layer enriched with plant wax on the surface, thus giving the material good oxygen barrier performance, water vapor barrier performance, mechanical properties, and biodegradability.

[0050] Example 1: A bio-based high-barrier biodegradable packaging material comprises the following formulation: 60 parts polylactic acid, 20 parts poly(butylene adipate / terephthalate), 10 parts starch, 2 parts nano clay, 5 parts polyvinyl alcohol, 3 parts glycerin, 1 part plant wax, 2 parts compatibilizer, 0.3 parts antioxidant, and 0.5 parts lubricant.

[0051] The nano-clay is an organically modified layered silicate with an interlayer spacing of 2.5 nm, and exists in the packaging material in a composite dispersion structure of exfoliated and intercalated states, wherein the mass proportion of the exfoliated state is 50%.

[0052] The polyvinyl alcohol has a degree of alcoholysis of 92% and a number-average molecular weight of 5 × 10⁻⁶. 4 It is distributed in the packaging material as a continuous phase and forms a hydrogen bond network structure with starch.

[0053] The starch is a pre-plasticized starch with a particle size of 17 μm and a crystallinity of 22%, and forms a transition interface structure between the dispersed phase and the continuous phase in the material; the starch surface contains hydroxyl functional groups, which form an interfacial bonding layer with polyvinyl alcohol and compatibilizer.

[0054] The compatibilizer is maleic anhydride-grafted polyester with a grafting rate of 1.75% and a number-average molecular weight of 3 × 10⁻⁶. 4 The compatibilizer is distributed at the interfaces of each phase in the material, forming an interface transition layer with a thickness of 60 nm.

[0055] The plant wax is carnauba wax, which has a melting point of 75°C. During the material forming process, it undergoes phase separation and migrates to the surface of the material to form a continuous hydrophobic layer with a thickness of 5.5 μm.

[0056] The glycerol exists in a molecularly dispersed state in the packaging material and forms hydrogen bonds with polyvinyl alcohol and starch, resulting in a glass transition temperature of 45°C.

[0057] The polylactic acid and poly(butylene adipate / terephthalate) form a bicontinuous structure in the packaging material, wherein the volume fraction of the flexible phase is 30%.

[0058] The lubricant is calcium stearate with a melting point of 85°C. It forms an interfacial lubrication layer with a thickness of 30 nm during the packaging material processing.

[0059] A method for preparing bio-based high-barrier biodegradable packaging materials includes the following steps: S1. Pre-disperse the nano-clay and construct an initial barrier precursor system.

[0060] First, the nano-clay was dried at 90℃ for 6 hours to control its moisture content to 1.0%. The dried nano-clay was then added to a high-speed mixer for premixing with polyvinyl alcohol (PVA), which was pulverized to 70 mesh. The premixing speed was 850 r / min for 18 minutes, allowing the PVA particles to adsorb nano-clay sheets and form a coating.

[0061] S2. The starch is pre-plasticized to form a transition phase component.

[0062] The starch was dried at 80℃ for 4 hours to reduce its moisture content to 5%. Then, it was added to a mixing device with glycerol for pre-plasticization mixing at 75℃ for 25 minutes, so that the glycerol could penetrate into the starch granules to form a plasticized starch intermediate.

[0063] S3. Perform premixing of the main matrix to form a main matrix premix.

[0064] Polylactic acid (PLA) was vacuum dried at 60°C for 6 hours, and poly(butylene adipate / terephthalate) was dried at 70°C for 4 hours. The dried PLA, poly(butylene adipate / terephthalate), compatibilizer, antioxidant, and lubricant were then added to a high-speed mixer and mixed for 12 minutes at 40°C. The compatibilizer was pre-contaminated with the poly(butylene adipate / terephthalate).

[0065] S4. Perform melt blending and extrusion to obtain the material masterbatch.

[0066] The barrier precursor system obtained in S1, the starch transition phase component obtained in S2, and the main matrix premix obtained in S3 were added to a twin-screw extruder for melt blending. The extruder temperature zones were all 160°C, the screw speed was 275 r / min, and the average residence time of the material in the barrel was 75 s. The extruded melt was cooled and pelletized to obtain the masterbatch.

[0067] S5. Perform molding processing to form a hydrophobic layer on the surface of the material.

[0068] The plant wax was premixed with the masterbatch obtained from S4 and then cast in a film at a temperature of 162℃. By adjusting the traction ratio, the plant wax was enriched on the surface of the melt. After cooling and solidification, a continuous layer was formed. The film thickness was 85μm.

[0069] S6. Perform shaping, adjustment, and post-processing.

[0070] The molded material was treated at 65℃ for 6 hours and then placed in an environment with a temperature of 25℃ and a relative humidity of 50% for 24 hours. After treatment, the material formed a layered structure, an intermediate region structure, and a surface structure.

[0071] Example 2: A bio-based high-barrier biodegradable packaging material comprises the following formulation: 75 parts polylactic acid, 35 parts polybutylene adipate / terephthalate, 20 parts starch, 5 parts nano clay, 12.5 parts polyvinyl alcohol, 6.5 parts glycerin, 3 parts plant wax, 4 parts compatibilizer, 0.65 parts antioxidant, and 1.25 parts lubricant.

[0072] The nano-clay is an organically modified layered silicate with an interlayer spacing of 2.5 nm, and exists in the packaging material in a composite dispersion structure of exfoliated and intercalated states, wherein the mass proportion of the exfoliated state is 50%.

[0073] The polyvinyl alcohol has a degree of alcoholysis of 92% and a number-average molecular weight of 5 × 10⁻⁶. 4 It is distributed in the packaging material as a continuous phase and forms a hydrogen bond network structure with starch.

[0074] The starch is a pre-plasticized starch with a particle size of 17 μm and a crystallinity of 22%, and forms a transition interface structure between the dispersed phase and the continuous phase in the material; the starch surface contains hydroxyl functional groups, which form an interfacial bonding layer with polyvinyl alcohol and compatibilizer.

[0075] The compatibilizer is maleic anhydride-grafted polyester with a grafting rate of 1.75% and a number-average molecular weight of 3 × 10⁻⁶. 4 The compatibilizer is distributed at the interfaces of each phase in the material, forming an interface transition layer with a thickness of 60 nm.

[0076] The plant wax is carnauba wax, which has a melting point of 75°C. During the material forming process, it undergoes phase separation and migrates to the surface of the material to form a continuous hydrophobic layer with a thickness of 5.5 μm.

[0077] The glycerol exists in a molecularly dispersed state in the packaging material and forms hydrogen bonds with polyvinyl alcohol and starch, resulting in a glass transition temperature of 45°C.

[0078] The polylactic acid and poly(butylene adipate / terephthalate) form a bicontinuous structure in the packaging material, wherein the volume fraction of the flexible phase is 30%.

[0079] The lubricant is calcium stearate with a melting point of 85°C. It forms an interfacial lubrication layer with a thickness of 30 nm during the packaging material processing.

[0080] A method for preparing bio-based high-barrier biodegradable packaging materials includes the following steps: S1. Pre-disperse the nano-clay and construct an initial barrier precursor system.

[0081] First, the nano-clay was dried at 90℃ for 6 hours to control its moisture content to 1.0%. The dried nano-clay was then added to a high-speed mixer for premixing with polyvinyl alcohol (PVA), which was pulverized to 70 mesh. The premixing speed was 850 r / min for 18 minutes, allowing the PVA particles to adsorb nano-clay sheets and form a coating.

[0082] S2. The starch is pre-plasticized to form a transition phase component.

[0083] The starch was dried at 80℃ for 4 hours to reduce its moisture content to 5%. Then, it was added to a mixing device with glycerol for pre-plasticization mixing at 75℃ for 25 minutes, so that the glycerol could penetrate into the starch granules to form a plasticized starch intermediate.

[0084] S3. Perform premixing of the main matrix to form a main matrix premix.

[0085] Polylactic acid (PLA) was vacuum dried at 60°C for 6 hours, and poly(butylene adipate / terephthalate) was dried at 70°C for 4 hours. The dried PLA, poly(butylene adipate / terephthalate), compatibilizer, antioxidant, and lubricant were then added to a high-speed mixer and mixed for 12 minutes at 40°C. The compatibilizer was pre-contaminated with the poly(butylene adipate / terephthalate).

[0086] S4. Perform melt blending and extrusion to obtain the material masterbatch.

[0087] The barrier precursor system obtained in S1, the starch transition phase component obtained in S2, and the main matrix premix obtained in S3 were added to a twin-screw extruder for melt blending. The extruder temperature zones were all 160°C, the screw speed was 275 r / min, and the average residence time of the material in the barrel was 75 s. The extruded melt was cooled and pelletized to obtain the masterbatch.

[0088] S5. Perform molding processing to form a hydrophobic layer on the surface of the material.

[0089] The plant wax was premixed with the masterbatch obtained from S4 and then cast in a film at a temperature of 162℃. By adjusting the traction ratio, the plant wax was enriched on the surface of the melt. After cooling and solidification, a continuous layer was formed. The film thickness was 85μm.

[0090] S6. Perform shaping, adjustment, and post-processing.

[0091] The molded material was treated at 65℃ for 6 hours and then placed in an environment with a temperature of 25℃ and a relative humidity of 50% for 24 hours. After treatment, the material formed a layered structure, an intermediate region structure, and a surface structure.

[0092] Example 3: A bio-based high-barrier biodegradable packaging material comprises the following formulation: 90 parts polylactic acid, 50 parts polybutylene adipate / terephthalate, 30 parts starch, 8 parts nano clay, 20 parts polyvinyl alcohol, 10 parts glycerin, 5 parts plant wax, 6 parts compatibilizer, 1 part antioxidant, and 2 parts lubricant.

[0093] The nano-clay is an organically modified layered silicate with an interlayer spacing of 2.5 nm, and exists in the packaging material in a composite dispersion structure of exfoliated and intercalated states, wherein the mass proportion of the exfoliated state is 50%.

[0094] The polyvinyl alcohol has a degree of alcoholysis of 92% and a number-average molecular weight of 5 × 10⁻⁶. 4 It is distributed in the packaging material as a continuous phase and forms a hydrogen bond network structure with starch.

[0095] The starch is a pre-plasticized starch with a particle size of 17 μm and a crystallinity of 22%, and forms a transition interface structure between the dispersed phase and the continuous phase in the material; the starch surface contains hydroxyl functional groups, which form an interfacial bonding layer with polyvinyl alcohol and compatibilizer.

[0096] The compatibilizer is maleic anhydride-grafted polyester with a grafting rate of 1.75% and a number-average molecular weight of 3 × 10⁻⁶. 4 The compatibilizer is distributed at the interfaces of each phase in the material, forming an interface transition layer with a thickness of 60 nm.

[0097] The plant wax is carnauba wax, which has a melting point of 75°C. During the material forming process, it undergoes phase separation and migrates to the surface of the material to form a continuous hydrophobic layer with a thickness of 5.5 μm.

[0098] The glycerol exists in a molecularly dispersed state in the packaging material and forms hydrogen bonds with polyvinyl alcohol and starch, resulting in a glass transition temperature of 45°C.

[0099] The polylactic acid and poly(butylene adipate / terephthalate) form a bicontinuous structure in the packaging material, wherein the volume fraction of the flexible phase is 30%.

[0100] The lubricant is calcium stearate with a melting point of 85°C. It forms an interfacial lubrication layer with a thickness of 30 nm during the packaging material processing.

[0101] A method for preparing bio-based high-barrier biodegradable packaging materials includes the following steps: S1. Pre-disperse the nano-clay and construct an initial barrier precursor system.

[0102] First, the nano-clay was dried at 90℃ for 6 hours to control its moisture content to 1.0%. The dried nano-clay was then added to a high-speed mixer for premixing with polyvinyl alcohol (PVA), which was pulverized to 70 mesh. The premixing speed was 850 r / min for 18 minutes, allowing the PVA particles to adsorb nano-clay sheets and form a coating.

[0103] S2. The starch is pre-plasticized to form a transition phase component.

[0104] The starch was dried at 80℃ for 4 hours to reduce its moisture content to 5%. Then, it was added to a mixing device with glycerol for pre-plasticization mixing at 75℃ for 25 minutes, so that the glycerol could penetrate into the starch granules to form a plasticized starch intermediate.

[0105] S3. Perform premixing of the main matrix to form a main matrix premix.

[0106] Polylactic acid (PLA) was vacuum dried at 60°C for 6 hours, and poly(butylene adipate / terephthalate) was dried at 70°C for 4 hours. The dried PLA, poly(butylene adipate / terephthalate), compatibilizer, antioxidant, and lubricant were then added to a high-speed mixer and mixed for 12 minutes at 40°C. The compatibilizer was pre-contaminated with the poly(butylene adipate / terephthalate).

[0107] S4. Perform melt blending and extrusion to obtain the material masterbatch.

[0108] The barrier precursor system obtained in S1, the starch transition phase component obtained in S2, and the main matrix premix obtained in S3 were added to a twin-screw extruder for melt blending. The extruder temperature zones were all 160°C, the screw speed was 275 r / min, and the average residence time of the material in the barrel was 75 s. The extruded melt was cooled and pelletized to obtain the masterbatch.

[0109] S5. Perform molding processing to form a hydrophobic layer on the surface of the material.

[0110] The plant wax was premixed with the masterbatch obtained from S4 and then cast in a film at a temperature of 162℃. By adjusting the traction ratio, the plant wax was enriched on the surface of the melt. After cooling and solidification, a continuous layer was formed. The film thickness was 85μm.

[0111] S6. Perform shaping, adjustment, and post-processing.

[0112] The molded material was treated at 65℃ for 6 hours and then placed in an environment with a temperature of 25℃ and a relative humidity of 50% for 24 hours. After treatment, the material formed a layered structure, an intermediate region structure, and a surface structure.

[0113] Comparative Example 1: Using a formulation system that is basically the same as in Example 2, key barrier-related components such as nano-clay, polyvinyl alcohol and plant wax were removed, and only basic biodegradable systems such as polylactic acid, PBAT and starch were retained. This was mainly used to verify the contribution of each functional component in the "multi-level barrier structure" to the barrier performance.

[0114] Specifically, the following formulas are included: 75 parts polylactic acid, 35 parts polybutylene adipate / terephthalate, 20 parts starch, 0 parts nano clay, 6.5 parts glycerin, 4 parts compatibilizer, 0.65 parts antioxidant, and 1.25 parts lubricant.

[0115] Comparative Example 2: Using a formulation system that is basically the same as in Example 2, the barrier functional components such as nano-clay, polyvinyl alcohol and plant wax were retained, but the compatibilizer was removed. It was mainly used to verify the key role of interfacial compatibility regulation in material performance.

[0116] Specifically, the following formulas are included: 75 parts polylactic acid, 35 parts poly(dibutyl adipate / terephthalate), 20 parts starch, 5 parts nano clay, 12.5 parts polyvinyl alcohol, 6.5 parts glycerin, 3 parts plant wax, 0 parts compatibilizer, 0.65 parts antioxidant, and 1.25 parts lubricant.

[0117] The materials prepared in Examples 1-3 and Comparative Examples 1-2 were subjected to the tests shown in Table 1 below to verify the actual effect of the coating.

[0118] Table 1

[0119] By conducting multiple tests on Examples 1-3 and Comparative Examples 1-2, including oxygen permeability, water vapor permeability, tensile properties, elongation at break, and degradation properties, it can be seen that the formulation of the present invention achieves a significantly better synergistic effect in terms of barrier properties and mechanical properties than the comparative examples.

[0120] First, regarding oxygen barrier performance, Examples 2 and 3 showed a significantly better performance trend than Example 1, and were also significantly better than Comparative Example 1. The reason for this is that in the example systems, nano-clay and polyvinyl alcohol (PVA) worked together to form a continuous or semi-continuous barrier structure. The nano-clay extended the gas diffusion path through layered orientation, while PVA and starch formed a dense structural region. Together, they significantly tortuoused the oxygen diffusion path within the material. In contrast, Comparative Example 1, lacking both nano-clay and PVA, relied solely on a polylactic acid (PLA) and starch system, resulting in a shorter gas diffusion path and thus a significantly higher oxygen permeability. Furthermore, although Comparative Example 2 contained nano-clay and PVA, the lack of a compatibilizer led to poor interfacial bonding and localized interfacial defects, disrupting the continuity of the barrier path and resulting in overall lower barrier performance than Example 2.

[0121] Secondly, in terms of water vapor barrier performance, all examples showed significantly better results than the comparative examples, with Example 3 performing best. This is mainly attributed to the migration of plant wax to the surface during material molding, forming a continuous hydrophobic layer that makes it difficult for water molecules to be adsorbed and penetrate the material surface; at the same time, the internal nano-clay and PVA / starch barrier regions further slowed down water vapor diffusion. In contrast, Comparative Example 1, due to the absence of plant wax, had a more hydrophilic surface, allowing water vapor to easily penetrate the material, resulting in a significantly higher water vapor permeability; although Comparative Example 2 contained plant wax, due to insufficient interfacial compatibility and the presence of microscopic defect channels within the material, water vapor could still diffuse rapidly along the interface, thus its barrier performance was still unsatisfactory.

[0122] Furthermore, regarding mechanical properties, the overall systems in the examples exhibited a good balance between tensile strength and elongation at break. Example 2 demonstrated superior comprehensive mechanical properties, exhibiting both high strength and good toughness, which is closely related to the rational phase structure formed by polylactic acid and PBAT, as well as the compatibilizer-enhanced interfacial bonding. Comparative Example 1, lacking the support of nanostructured fillers and barrier phases, relied primarily on the matrix material for its mechanical properties, exhibiting moderate strength and toughness. Comparative Example 2, due to the absence of a compatibilizer and poor interfacial bonding, was prone to interfacial delamination under stress, resulting in a significant decrease in elongation at break and exhibiting brittle fracture characteristics.

[0123] In addition, in terms of degradation performance, both the examples and the comparative examples maintain good degradability. However, due to the presence of starch, PVA and multiphase structure, the examples form more degradation initiation sites, resulting in more uniform degradation behavior of the materials under natural environment or composting conditions. In contrast, the degradation process of the comparative example system is relatively simple, and the degradation rate distribution is uneven.

[0124] In summary, this invention achieves synergistic optimization of the material's gas barrier, water vapor barrier, mechanical properties, and degradation performance by constructing a multi-level structure consisting of a "nanoclay tortuous barrier path—polyvinyl alcohol / starch dense barrier region—plant wax surface hydrophobic layer" and combining it with a compatibilizer to regulate the interfacial state. Compared to the comparative example, this technical solution not only significantly improves barrier performance but also avoids interfacial defects caused by the simple superposition of components.

[0125] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A bio-based high-barrier biodegradable packaging material, characterized in that, The material comprises the following formula by weight: Polylactic acid 60-90 parts; 20-50 parts of poly(butylene adipate / terephthalate); 10-30 parts starch; 2-8 parts of nano-clay; 5-20 parts of polyvinyl alcohol; 3-10 parts glycerin; 1-5 parts of plant wax; 2-6 parts compatibilizer; Antioxidant 0.3 to 1 part; Lubricant 0.5 to 2 parts.

2. The bio-based high-barrier biodegradable packaging material according to claim 1, characterized in that, The nano-clay is an organically modified layered silicate with an interlayer spacing controlled in the range of 1.5 to 3.5 nm. It exists in the packaging material in a composite dispersion structure of exfoliated and intercalated states, wherein the mass proportion of the exfoliated state is 30% to 70%.

3. The bio-based high-barrier biodegradable packaging material according to claim 1, characterized in that, The degree of alcoholysis of the polyvinyl alcohol is 85%–99%, and the number average molecular weight is 2 × 10⁻⁶. 4 ~8×10 4 It is distributed in the packaging material in the form of a continuous or semi-continuous phase and forms a hydrogen bond network structure with starch.

4. The bio-based high-barrier biodegradable packaging material according to claim 1, characterized in that, The starch is a pre-plasticized or esterified starch with a particle size of 5-30 μm and a crystallinity of 10%-35%, and forms a transition interface structure between the dispersed phase and the continuous phase in the material. The starch surface contains hydroxyl or ester functional groups, which form a stable interfacial bonding layer with polyvinyl alcohol and compatibilizer.

5. The bio-based high-barrier biodegradable packaging material according to claim 1, characterized in that, The compatibilizer is maleic anhydride-grafted polyester or grafted polyolefin, with a grafting rate of 0.5% to 3.0% and a number-average molecular weight of 1×10⁻⁶. 4 ~5×10 4 ; The compatibilizer is distributed at the interfaces of each phase in the material, forming an interfacial transition layer with a thickness of 20-100 nm.

6. The bio-based high-barrier biodegradable packaging material according to claim 1, characterized in that, The plant wax is a natural wax substance with a melting point in the range of 60 to 90°C. During the material forming process, it undergoes phase separation and migrates to the surface of the material to form a continuous hydrophobic layer with a thickness of 1 to 10 μm.

7. The bio-based high-barrier biodegradable packaging material according to claim 1, characterized in that, The glycerol exists in a molecularly dispersed state in the packaging material. Its glass transition temperature is adjusted by forming hydrogen bonds with polyvinyl alcohol and starch, thereby reducing the glass transition temperature to the range of 30-60°C.

8. The bio-based high-barrier biodegradable packaging material according to claim 1, characterized in that, The polylactic acid and poly(butylene adipate / terephthalate) form an "island structure" or "bicontinuous structure" in the packaging material, wherein the volume fraction of the flexible phase is 20% to 40%.

9. The bio-based high-barrier biodegradable packaging material according to claim 1, characterized in that, The lubricant is a fatty acid or its metal salt, with a melting point of 50-120°C, and forms an interfacial lubrication layer during the processing of packaging materials. The thickness of the interfacial lubrication layer is 10-50 nm.

10. A method for preparing a bio-based high-barrier degradable packaging material, comprising preparing the material based on the bio-based high-barrier degradable packaging material according to any one of claims 1-9, characterized in that, Includes the following steps: S1. Pre-disperse the nano-clay and construct an initial barrier precursor system; S2. Pre-plasticize starch to form a transition phase component that matches the barrier precursor system; S3. Perform premixing of the main matrix to form a main matrix premix that can support the barrier structure; S4. The barrier precursor system, starch transition phase component and main matrix premix are melt-blended and extruded to construct a multi-phase synergistic high barrier biodegradable material masterbatch. S5. Introduce plant wax into the molding stage and perform secondary heat treatment to form a hydrophobic barrier layer on the surface of the material. S6. Perform shaping and post-treatment on the molded material to stabilize the internal barrier structure and the surface hydrophobic structure.

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