Controllable layered distribution PBAT-based degradable lunch box material and preparation method thereof, and degradable lunch box
By controlling the molecular weight ratio and phase structure of PBAT-based biodegradable lunchbox materials and combining them with pH-responsive microcapsules, the problem of aromatic microplastic residues in PBAT-based lunchboxes was solved, achieving a balance between efficient degradation and mechanical properties.
Patent Information
- Application Number
- CN202610580522.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-04-29
- Publication Date
- 2026-07-03
AI Technical Summary
Existing PBAT-based biodegradable lunch boxes have the problem of residual aromatic chain segments forming microplastics during the degradation process, and the degradation rate is greatly affected by environmental factors, which cannot meet food safety requirements.
The PBAT-based biodegradable lunchbox material with controllable layered distribution achieves simultaneous and rapid degradation of chain segments by adjusting the molecular weight ratio and phase structure of aliphatic and aromatic segments, combined with pH-responsive microcapsules and water-soluble porogens.
The lunchbox was efficiently degraded under industrial composting conditions, with a significant reduction in microplastic residues, mechanical properties that meet usage requirements, a degradation rate of over 90%, and an aromatic unit residue rate of less than 5%.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of polymer material processing and molding technology, specifically to a controllable layered distribution of PBAT-based biodegradable lunchbox material and its preparation method, as well as a biodegradable lunchbox. Background Technology
[0002] Existing biodegradable lunch boxes generally suffer from two major problems: "incomplete degradation" and "microplastic pollution." Studies have shown that commercially available PBAT-based lunch boxes, after being treated under industrial composting conditions for 478 days (16 months), still have macroscopic residues, with a mass loss of only 57-66%, indicating that they have not completely disappeared. The fundamental reason is that after the rapid degradation of natural components such as starch, the degradation of the PBAT polyester phase is slow. Its aliphatic segments (butylene adipate) are preferentially attacked and broken by microorganisms, while the aromatic segments (terephthalic acid units) are enriched and remain due to their stable structure, forming microplastic particles (<5μm). More seriously, after the lunch box is exposed to ultraviolet radiation or microwave heating during use, PBAT will undergo photo-oxidative cross-linking or thermal cross-linking, leading to an increase in degradation activation energy and further slowing down the overall biodegradation rate. Current laboratory testing standards (such as ISO 17556) are conducted at a constant 25°C and 60% humidity, with a 90% mineralization rate determining complete degradation. However, these conditions cannot realistically simulate the complex environments experienced by discarded lunchboxes, including temperature fluctuations (-10°C to 70°C), pH changes (pH 5-9), and mechanical breakage. Residual microplastics can accumulate through the food chain, posing a potential risk to food safety.
[0003] In existing technologies, the blending of PBAT with PLA and other materials is usually carried out by simple melt blending, which makes it difficult to control the phase structure, resulting in a mismatch in the degradation rates of each component during the degradation process and easily generating microplastic fragments. Summary of the Invention
[0004] As described above in the prior art, one of the objectives of this invention is to provide a controllable layered distribution of PBAT-based biodegradable lunchbox material, thereby solving the problem of aromatic microplastic residues caused by asynchronous chain segment degradation in PBAT-based lunchboxes.
[0005] The second objective of this invention is to provide a method for preparing PBAT-based biodegradable lunchbox materials with controllable layered distribution, which can successfully prepare biodegradable lunchbox materials.
[0006] The third objective of this invention is to provide a biodegradable lunchbox.
[0007] One of the objectives of this invention is achieved through the following technical solution: A controllable layered distribution of PBAT-based biodegradable lunch box material, comprising polybutylene adipate-terephthalate copolymer (PBAT), which is composed of aliphatic segments (BA segments) and aromatic segments (BT segments); The PBAT is a multiblock copolymer with a controllable layered distribution tendency, wherein the BA segments and BT segments are arranged in a quasi-alternating pattern, and the sequence regularity index η≥0.65, wherein η is calculated by measuring the area ratio of the carbonyl carbon chemical shift splitting peak by ¹³C-NMR, and η = Ialternating / (Ialternating + I random). The BA segment is composed of multiple repeating units of butylene adipate, with a number-average molecular weight Mn of 3000-8000 g / mol, and the BT segment is composed of multiple repeating units of butylene terephthalate, with a number-average molecular weight Mn of 15000-35000 g / mol. The molecular weight ratio of the BA segment to the BT segment is 1:3 to 1:5; The melt flow index of the PBAT is 3-8 g / 10 min (2.16 kg at 190℃). After melt blending and controlled heat treatment, the controllable layered PBAT-based biodegradable lunchbox material can selectively exhibit one of the following three phase structures: (a) Island structure: The BA phase is dispersed in microspheres in the BT continuous phase, with a phase region size of 0.1-1 μm; (b) Controllable layered bicontinuous phase structure: BA phase region and BT phase region are arranged alternately, and the phase region size is 0.5-2μm.
[0008] Furthermore, it further comprises 0.3-0.8 wt% of pH-responsive microcapsules, wherein the core material of the pH-responsive microcapsules is a complex of lipase and citrate monoglyceride, and the wall material of the pH-responsive microcapsules is polylactic acid, which can rupture in an environment with a pH below 6.5. The pH-responsive microcapsules rupture and release the core material in an acidic environment generated by the degradation of BA segments.
[0009] Furthermore, the phase structure of PBAT is a layered bicontinuous phase, in which the BA phase region and the BT phase region are arranged alternately, and the phase region size is 0.5-2μm.
[0010] Furthermore, it further contains 5-15 wt% of a water-soluble porogen, polyethylene glycol (PEG2000), which dissolves upon contact with water to form micropores with an average pore size of 50-200 nm.
[0011] Furthermore, when the compound further includes 5-25 parts of bio-based filler, it also includes 0.5-2 parts of reactive compatibilizer. The reactive compatibilizer forms a PBAT graft copolymer in situ during extrusion, maintaining the continuity of the PBAT phase region. Preferably, it is a starch-g-PBAT graft copolymer. The second objective of this invention is achieved by the following technical solution: A method for manufacturing a controllable layered PBAT-based biodegradable lunchbox material includes the following steps: S1. Synthesis of alternating block PBAT prepolymer: Butylene adipate prepolymer (BA prepolymer, Mn=3000-8000 g / mol) and butylene terephthalate prepolymer (BT prepolymer, Mn=15000-35000 g / mol) were mixed at a molar ratio of 1:3 to 1:5. 0.03-0.08 wt% tetrabutyl titanate catalyst was added, and the transesterification reaction was carried out at 240-250 °C and a vacuum degree of 50-100 Pa for 2-3 hours under an inert atmosphere. Vacuum treatment was used to remove reaction byproducts. This post-treatment step controlled the melt index of the PBAT copolymer to 3-8 g / 10 min (190 °C, 2.16 kg), resulting in a multi-block copolymer with a controllable layered distribution tendency, thus obtaining the PBAT copolymer. S2. Melt blending: The PBAT copolymer obtained in step S1 is melt blended with 5-25 parts of optional bio-based filler and 5-15 wt% polyethylene glycol (PEG 2000) processing aid in a twin-screw extruder at 160-180℃, with a screw speed of 150-200 rpm and a residence time of 2-3 minutes to obtain granules, which are biodegradable lunch box materials. PEG 2000 acts as a water-soluble pore-forming agent and dissolves in subsequent use to form 50-200 nm micropores. After melt blending, by controlling the subsequent heat treatment process, three different phases of biodegradable lunchbox materials can be obtained: Rapid cooling: Cooling rate ≥ 50℃ / s, resulting in a biodegradable lunchbox material with an island structure; Slow cooling and annealing: cooling rate ≤5℃ / s, annealing at 100-140℃ for 2-6h to obtain biodegradable lunch box material with a controllable layered distribution of two continuous phases; S3. pH-responsive microcapsule loading: After the granules obtained in step S2 are thermoformed into a lunchbox semi-finished product, a pH-responsive microcapsule dispersion is sprayed or dipped onto the surface of the lunchbox, or the microcapsule dispersion is pre-coated and bonded to the surface of the granules before thermoforming, so that the pH-responsive microcapsules are loaded onto the material surface. The microcapsule loading amount is 0.3-0.8 wt%. The pH-responsive microcapsules were prepared by the following method: lipase (activity 10000-15000 U / g) and glyceryl citrate were dissolved in water at a mass ratio of 1:2-1:3 to prepare a core material solution with a solid content of 15-20%; polylactic acid (Mn=8000-12000) was dissolved in dichloromethane to prepare a wall material solution with a content of 10-12 wt%; microcapsules with a particle size of 20-50 μm and an encapsulation efficiency >85% were obtained by solvent evaporation at a wall material / core material mass ratio of 1:1-1.2:1 and a stirring speed of 800-1200 rpm.
[0012] The third objective of this invention is achieved by the following technical solution: A biodegradable lunch box is made of biodegradable lunch box material through a thermoforming process. The lunch box has a wall thickness of 0.4-0.8 mm, a volume of 500-1000 mL, a tensile strength retention rate of >90% during its service life, and a degradation rate of >90% within 120 days under industrial composting conditions.
[0013] Furthermore, the thermoforming process includes the following steps: Sheet extrusion: The granules obtained in step S2 are melted and plasticized in a single screw extruder at 160-180℃, and extruded into sheets through a coat hanger die. The sheet thickness is 0.4-0.8mm, the extrusion rate is 3-5m / min, the cooling roller temperature is 15-20℃, and the cooling rate is >50℃ / s. Vacuum forming: The sheet material is heated to above the softening point but below the melting point, i.e., the temperature range is 150-160℃, the heating time is 20-30 seconds, and it is vacuum formed into a lunch box under a vacuum degree of 0.06-0.08MPa. The mold temperature is 30-50℃, the forming time is 3-5 seconds, and the pressure is held and cooled for 10-15 seconds.
[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention provides a PBAT-based biodegradable lunch box material with controllable layered distribution, 1. Matching chain segment length: The molecular weight of BA chain segment is reduced to the range of efficient microbial metabolism (3000-8000g / mol), and the BT chain segment is correspondingly shortened to 15000-35000g / mol, so that the degradation endpoints of the two are synchronized; 2. Block structure with controllable layered distribution: The PBAT is a multi-block copolymer with controllable layered distribution tendency, avoiding the uneven distribution of degradation sites caused by random copolymerization; 3. pH-responsive microcapsules: Lipase microcapsules are pre-embedded. The acidic environment (pH<6.5) generated by BA degradation triggers the wall material to break, releasing microcapsules to attack BT chain segments, forming a positive feedback cycle of degradation; 4. Bicontinuous phase with controllable layered distribution: Replacing the traditional "island structure", after the BA phase degrades, the BT phase loses mechanical support and collapses, the specific surface area increases by 10-15 times, and the degradation rate is increased exponentially. The lunchbox of this invention exhibits an overall degradation rate of >92% and an aromatic unit residue rate of <5% (compared to >40% for traditional PBAT) within 120 days under industrial composting conditions (58℃±2℃, humidity 65%). The amount of microplastics (<5μm) generated is <4.2%, and its mechanical properties meet the requirements for holding hot food (85℃) and cold chain (-18℃). Detailed Implementation
[0015] The present invention will now be further described in conjunction with specific embodiments. It should be noted that, without conflict, the embodiments or technical features described below can be arbitrarily combined to form new embodiments. Example
[0016] This embodiment provides a PBAT-based biodegradable lunch box material with controllable layered distribution, comprising polybutylene adipate terephthalate copolymer (PBAT), which is composed of aliphatic segments (BA segments) and aromatic segments (BT segments); PBAT is a multiblock copolymer with a controllable layered distribution tendency, in which the BA segments and BT segments are arranged in a quasi-alternating pattern, and the sequence regularity index η≥0.65. η is calculated by measuring the area ratio of the carbonyl carbon chemical shift splitting peak by ¹³C-NMR, and η = Ialternating / (Ialternating + I random). The BA segment is composed of multiple repeating units of butylene adipate, with a number-average molecular weight Mn of 3000-8000 g / mol, while the BT segment is composed of multiple repeating units of butylene terephthalate, with a number-average molecular weight Mn of 15000-35000 g / mol. The molecular weight ratio of BA segment to BT segment is 1:3 to 1:5; The melt flow index of PBAT is 3-8 g / 10 min (2.16 kg at 190℃). After melt blending and controlled heat treatment, the controllable layered PBAT-based biodegradable lunchbox material can selectively exhibit one of the following three phase structures: Controllable layered bicontinuous phase structure: The BA phase region and the BT phase region exhibit a controllable layered distribution tendency, forming a controllable layered multiblock copolymer with a phase region size of 0.5-2μm.
[0017] In this embodiment, the formation mechanism of the controllable layered distribution tendency of PBAT is as follows: 1. Reaction kinetic control: Tetrabutyl titanate catalysts are 3-5 times more efficient at catalytic reactions between hydroxyl and ester groups than those between ester groups. When the hydroxyl groups of BA prepolymer react with the ester groups of BT prepolymer, the newly formed end groups have reduced activity and tend to react with the active end groups of another prepolymer. After the hydroxyl groups (-OH) of BA prepolymer react with the ester groups (-COO-) of BT prepolymer, the newly formed end groups (still hydroxyl groups) are attached to the rigid BT chain segments, which reduces their steric accessibility and nucleophilicity. They are difficult to react with the equally "sluggish" BT ester groups, but can react efficiently with the "flexible" BA hydroxyl groups, thereby driving the generation of alternating sequences.
[0018] 2. Thermodynamics: Driving force of phase separation BA segment: solubility parameter δ≈19.2(J / cm³)^0.5, strong hydrophilicity, and good compatibility with polar groups; BT segment: solubility parameter δ≈22.5(J / cm³)^0.5, relatively hydrophobic, benzene ring structure repels polar molecules. Thermodynamic spontaneous processes: In the molten state (240-250℃), the BA and BT segments tend to separate into micro-phases due to differences in solubility parameters, but the reactivity of the terminal hydroxyl / ester groups forces them to undergo transesterification at the phase interface. The competitive result is the formation of an alternating arrangement of bicontinuous phases rather than macro-phase separation, because complete separation would lead to an increase in the system's free energy.
[0019] Step S1, the transesterification reaction, adopts a two-step process: first, BA prepolymer and BT prepolymer are prepared separately, and then they are mixed for transesterification. The BA prepolymer is prepared by pre-condensation of adipic acid and butanediol at 180-200℃ and atmospheric pressure for 2 hours, and the BT prepolymer is prepared by pre-condensation of dimethyl terephthalate and butanediol at 220-240℃ and vacuum for 3 hours.
[0020] In this embodiment, the phase structure of PBAT is a controllable layered bicontinuous phase structure with a phase region size of 0.5-2 μm.
[0021] In this embodiment, it further includes 5-15 wt% of a water-soluble porogen, polyethylene glycol (PEG2000), which dissolves upon contact with water or compost leachate to form micropores with an average pore size of 50-200 nm.
[0022] In this embodiment, when 5-25 parts of bio-based filler are further included, 0.5-2 parts of reactive compatibilizer are also included. The reactive compatibilizer forms a starch-g-PBAT graft copolymer in situ during the extrusion process, maintaining the continuity of the PBAT phase region.
[0023] This embodiment also provides a method for preparing a controllable layered distribution of PBAT-based biodegradable lunchbox material, including the following steps: Alternating Block PBAT Synthesis S1. Butylene adipate prepolymer (Mn=5200g / mol) and butylene terephthalate prepolymer (Mn=22000g / mol) were mixed at a molar ratio of 1:4, and 0.05wt% tetrabutyl titanate was added. The mixture was subjected to transesterification reaction at 240℃ and 50Pa vacuum for 2.5 hours to obtain a multi-block copolymer with a controllable layered distribution tendency. Vacuum treatment was used to remove reaction byproducts. This post-treatment step controlled the melt index of the PBAT copolymer at 5.8 g / 10min (190℃ 2.16kg). S2. Melt Blending: The PBAT copolymer obtained in step S1 is melt-blended with 5-25 parts of optional bio-based filler and 5-15 wt% polyethylene glycol (PEG 2000) processing aid in a twin-screw extruder at 160-180℃, screw speed 150-200 rpm, residence time 2-3 minutes to obtain granules, which are biodegradable lunch box materials. PEG 2000 acts as a water-soluble pore-forming agent, dissolving to form 50-200 nm micropores during subsequent use. After melt blending, the material is slowly cooled and annealed: cooling rate ≤5℃ / s, annealing at 100-140℃ for 2-6 hours to obtain a biodegradable lunch box material with a controllable layered distribution of two continuous phases. In this embodiment, the twin-screw extruder in step S2 is a co-rotating twin-screw extruder with a screw diameter of 35-50 mm and an aspect ratio of L / D = 40-48. The screw assembly includes at least 3 sets of 45° / 90° kneading block elements to achieve the strong shear dispersion required for gradient copolymerization.
[0024] In this embodiment, the melt blending in step S2 adopts a side-feeding process. The bio-based filler is added through the side feed port in the third screw section, and the feeding rate is controlled at 5-10 kg / h to avoid the starch staying in the high-temperature zone of the barrel for too long, which would lead to thermal degradation.
[0025] This embodiment also provides a biodegradable lunch box, which is made of biodegradable lunch box material through a thermoforming process. The lunch box has a wall thickness of 0.4-0.8mm, a volume of 500-1000mL, a tensile strength retention rate of >90% during its service life, and a degradation rate of >90% within 120 days under industrial composting conditions.
[0026] Specifically, the thermoforming process includes the following steps: Sheet extrusion: The granules obtained in step S2 are melted and plasticized in a single screw extruder at 160-180℃, and extruded into sheets through a coat hanger die. The sheet thickness is 0.4-0.8mm, the extrusion rate is 3-5m / min, the cooling roller temperature is 15-20℃, and the cooling rate is >50℃ / s. Vacuum forming: The sheet material is heated to above the softening point but below the melting point, i.e., the temperature range is 150-160℃, the heating time is 20-30 seconds, and it is vacuum formed into a lunch box under a vacuum degree of 0.06-0.08MPa. The mold temperature is 30-50℃, the forming time is 3-5 seconds, and the pressure is held and cooled for 10-15 seconds.
[0027] Example 2 This embodiment provides a controllable layered distribution of PBAT-based biodegradable lunch box material, comprising polybutylene adipate terephthalate copolymer (PBAT) and pH-responsive microcapsules. The polybutylene adipate terephthalate copolymer is composed of aliphatic segments (BA segments) and aromatic segments (BT segments). PBAT is a multiblock copolymer with a controllable layered distribution tendency, in which the BA segments and BT segments are arranged in a quasi-alternating pattern, and the sequence regularity index η≥0.65. η is calculated by measuring the area ratio of the carbonyl carbon chemical shift splitting peak by ¹³C-NMR, and η = Ialternating / (Ialternating + I random). The BA segment is composed of multiple repeating units of butylene adipate, with a number-average molecular weight Mn of 3000-8000 g / mol, while the BT segment is composed of multiple repeating units of butylene terephthalate, with a number-average molecular weight Mn of 15000-35000 g / mol. The molecular weight ratio of BA segment to BT segment is 1:3 to 1:5; The melt flow index of PBAT is 3-8 g / 10 min (2.16 kg at 190℃). By controlling the processing conditions, materials can selectively exhibit the following phase structures: Controllable layered bicontinuous phase structure: The BA phase region and the BT phase region exhibit a controllable layered distribution tendency, forming a controllable layered multiblock copolymer with a phase region size of 0.5-2μm.
[0028] The core material of the pH-responsive microcapsules is a complex of lipase and glyceryl citrate, and the wall material is polylactic acid. The microcapsules rupture and release the core material in the acidic environment generated by the degradation of BA segments.
[0029] This embodiment also provides a method for preparing a controllable layered distribution of PBAT-based biodegradable lunchbox material, including the following steps: Alternating Block PBAT Synthesis S1. Butylene adipate prepolymer (Mn=5200g / mol) and butylene terephthalate prepolymer (Mn=22000g / mol) were mixed at a molar ratio of 1:4, and 0.05wt% tetrabutyl titanate was added. The mixture was subjected to transesterification reaction at 240℃ and 50Pa vacuum for 2.5 hours to obtain a multi-block copolymer with a controllable layered distribution tendency. Vacuum treatment was used to remove reaction byproducts. This post-treatment step controlled the melt index of the PBAT copolymer at 5.8 g / 10min (190℃ 2.16kg). S2. Preparation of pH-responsive microcapsules: The core material of the microcapsules is a complex of lipase and glyceryl citrate. Lipase (activity 10000 U / g) and glyceryl citrate are dissolved in water at a mass ratio of 1:2, with a solid content of 15%. Polylactic acid (Mn=10000) is used as the wall material, dissolved in dichloromethane (10wt%), with a wall material / core material mass ratio of 1:1. The microcapsules rupture and release the core material under the acidic environment generated by the degradation of BA segments. The microcapsules are prepared by solvent evaporation method with a stirring speed of 800 rpm, producing microcapsules with a particle size of 20-50 μm and an encapsulation rate >85%. After melt blending, the microcapsules are slowly cooled and annealed: cooling rate ≤5℃ / s, annealing at 100-140℃ for 2-6 h, to obtain a biodegradable lunch box material with a controllable layered distribution of a bicontinuous phase. S2. Melt blending: The PBAT copolymer obtained in step S1 is melt blended with 5-25 parts of optional bio-based filler and 5-15 wt% polyethylene glycol (PEG 2000) processing aid in a twin-screw extruder at 160-180℃, with a screw speed of 150-200 rpm and a residence time of 2-3 minutes to obtain granules, which are biodegradable lunch box materials. PEG 2000 acts as a water-soluble pore-forming agent and dissolves in subsequent use to form 50-200 nm micropores. S3. pH-responsive microcapsule loading: After the granules obtained in step S2 are thermoformed into a lunchbox semi-finished product, a pH-responsive microcapsule dispersion is sprayed or dipped onto the surface of the lunchbox, or the microcapsule dispersion is pre-coated and bonded to the surface of the granules before thermoforming, so that the pH-responsive microcapsules are loaded onto the material surface. The microcapsule loading amount is 0.3-0.8 wt%. The pH-responsive microcapsules were prepared by the following method: lipase (activity 10000-15000 U / g) and glyceryl citrate were dissolved in water at a mass ratio of 1:2-1:3 to prepare a core material solution with a solid content of 15-20%; polylactic acid (Mn=8000-12000) was dissolved in dichloromethane to prepare a wall material solution with a content of 10-12 wt%; microcapsules with a particle size of 20-50 μm and an encapsulation efficiency >85% were obtained by solvent evaporation at a wall material / core material mass ratio of 1:1-1.2:1 and a stirring speed of 800-1200 rpm.
[0030] To avoid lipase inactivation due to the high temperature (160-180℃) during melt blending, this invention sets the microcapsule loading process after thermoforming or during surface pre-coating. The microcapsules are dispersed in an aqueous medium (such as a 1-3 wt% polyvinyl alcohol aqueous solution) and attached to the surface of the lunchbox by spraying or dipping. During use, the microcapsules are located on the surface of the material. When the lunchbox is discarded and comes into contact with a composting environment, the acidic substances (succinic acid, adipic acid, etc.) produced by the degradation of the BA segments cause the local pH to drop below 6.5, triggering the hydrolysis and rupture of the microcapsule wall material (PLA), releasing lipase and glyceryl citrate. Glyceryl citrate further acidifies the microenvironment, and the lipase attacks the BT segments, forming a positive feedback loop of acidification-enzyme release-degradation.
[0031] Comparative Example 1 Comparative Example 1 provides a PBAT-based biodegradable lunchbox material. The poly(butylene adipate-terephthalate) copolymer is composed of aliphatic segments (BA segments) and aromatic segments (BT segments). PBAT does not have a bicontinuous phase structure with a controllable layered distribution.
[0032] Comparative Example 2 This comparative example provides a PBAT-based biodegradable lunchbox material with a controllable layered distribution, comprising polybutylene adipate terephthalate copolymer (PBAT) and pH-responsive microcapsules. The polybutylene adipate terephthalate copolymer is composed of aliphatic segments (BA segments) and aromatic segments (BT segments). PBAT has a controllable layered bicontinuous phase structure, where A is the BA segment and B is the BT segment, and n≥5; The number-average molecular weight (Mn) of the BA segment is 3000-8000 g / mol, and the number-average molecular weight (Mn) of the BT segment is 15000-35000 g / mol. The molecular weight ratio of BA segment to BT segment is 1:3 to 1:5; The melt flow index of PBAT is 3-8 g / 10 min (2.16 kg at 190℃). After melt blending, a controlled heat treatment process is applied, specifically, after melt blending, rapid cooling is performed at a rate ≥50℃ / s to obtain a biodegradable lunchbox material with an island structure, which can selectively exhibit the following phase structures: Island structure: The BA phase is dispersed in microspheres in the BT continuous phase, with a phase region size of 0.1-1 μm.
[0033] Experimental Example 1 Methods for testing molecular weight and chain segment distribution The number-average molecular weight (Mn), weight-average molecular weight (Mw), and molecular weight distribution index (PDI) of PBAT copolymers were determined by gel permeation chromatography (GPC) to verify the chain length matching effect.
[0034] Sample preparation: Dissolve pure PBAT particles or film samples in tetrahydrofuran (THF) at a concentration of 2.5 g / L, filter through a 0.45 μm PTFE membrane, and inject into a 2 mL sample vial. All samples are slightly turbid due to the presence of 24% starch filler and require ultrasonic dispersion for 15 minutes.
[0035] Test conditions: A Waterse2695 HPLC system equipped with a Waters2414 differential refractive index detector (RI) was used. The column setup consisted of PLgel MIXED-A (300 × 7.5 mm, 20 μm) + MIXED-B (10 μm) + MIXED-D (5 μm) in series. The mobile phase was THF containing 250 ppm butylparaben stabilizer, the flow rate was 1.0 mL / min, the column temperature was 40 °C, and the injection volume was 100 μL.
[0036] Calibration curves: Calibration curves were established using narrow-distribution polystyrene standards (580, 10440, 38640, 132900, 492500, 990500 g / mol), and data processing was performed using Empower3 software.
[0037] Data analysis: The BA segment (low temperature peak) and BT segment (high temperature peak) signals were separated by peak deconvolution, and the Mn value and BA / BT peak area ratio of each segment were calculated. The GPC method described above was used, with each sample measured in triplicate and the average value taken. The test results are shown in Table 1.
[0038] Table 1. Molecular weight distribution of PBAT segments in different formulations (GPC test)
[0039] Results analysis: Chain segment length control precision: The optimal sample was synthesized by a two-step method. The BA chain segment Mn=5050±160 g / mol and the BT chain segment Mn=20200±580 g / mol. The actual value deviated from the design value (5000 / 20000) by <3%, which proves that the synthesis process has high controllability.
[0040] Narrowing of molecular weight distribution: The PDI of the preferred sample decreased from 2.85 to 1.98 in the traditional PBAT, indicating that the alternating block structure makes the molecular chain length more uniform and reduces the heterogeneity of degradation sites.
[0041] BA / BT ratio optimization: The proportion of BA segments in the preferred sample was increased to 20.0%, which is close to the theoretical synchronous degradation ratio (calculated based on the degradation rate constant), while the proportion of traditional PBAT was only 13.0% due to the excessive length of BA segments, which could not form an effective degradation synergy.
[0042] Conclusion: GPC data directly verified the realization of the technical feature in claim 1, "BA segment Mn=3000-8000 g / mol, BT segment Mn=15000-35000 g / mol, ratio 1:3-1:5". Moreover, the preferred sample has a narrow molecular weight distribution and precise segment ratio, providing a structural basis for synchronous degradation.
[0043] Experiment Example 2 Experimental methods: Degradation tests were conducted according to GB / T19277.1-2011 (Industrial composting conditions), with a temperature of 58±2℃ and humidity of 65%. Sample dimensions were 50mm×50mm×0.6mm. Tensile strength was tested according to GB / T1040.3-2006. Microplastic residue was determined by using a laser particle size analyzer (Malvern Mastersizer 3000) to measure the proportion of particles <5μm after degradation. The residual rate of aromatic units was determined by HPLC-MS to measure the content of butylene terephthalate oligomers. The test results are shown in Table 2.
[0044] Table 2 Comparison of degradation performance of formulations with different chain segment lengths
[0045] Results analysis: Chain segment length matching effect: When the BA / BT molecular weight ratio was optimized from 1:6.7 to 1:4.0, the degradation rate after 120 days increased from 45.2% to 92.3%, and the microplastic residue decreased from 38.5% to 4.2%, proving that shortening the BT chain segment can simultaneously degrade to the endpoint.
[0046] Mechanical properties maintained: The tensile strength of the sample in Example 2 was only 5.8% lower than that of the traditional PBAT, but still far exceeded the national standard requirement of ≥15MPa, meeting the strength requirements for use in lunch boxes.
[0047] Critical threshold: BA segment Mn < 8000 g / mol is the key to ensuring efficient microbial metabolism, while BT segment Mn < 35000 g / mol can avoid degradation delay caused by excessive crystallinity.
[0048] Conclusion: The molecular weight range (BA: 3000-8000; BT: 15000-35000; ratio 1:3-1:5) is the optimal range for achieving a balance between simultaneous degradation and mechanical properties.
[0049] Experimental Example 3 Experimental Methods: Lunchbox samples containing microcapsules were placed in simulated compost leachate with an initial pH of 7.2. pH changes and lipase activity were periodically measured using the pNPP method. The activation energy for BT segment degradation was obtained by calculating the DSC curve using the Kissinger equation. The degradation induction period was defined as the time required for BT segment mass loss to reach 5%. The test results are shown in Table 3.
[0050] Table 3 Triggering effect of pH-responsive microcapsules
[0051] Results analysis: Positive feedback mechanism: When the microcapsule ruptures at pH < 6.0, it releases lipase, and the activation energy for BT segment degradation decreases from 85.2 kJ / mol to 58.2 kJ / mol, a reduction of 31.7%, while the reaction rate constant increases by about 10 times.
[0052] Time synergy: The citrate monoglyceride released from the 0.5wt% microcapsules can further acidify the microenvironment, reducing the pH to 5.5, accelerating the hydrolysis of BT ester bonds. The BT degradation induction period of the sample in Example 2 was shortened to 8 days, which perfectly matched the rapid degradation period of the BA chain segment (7-10 days), avoiding the "degradation vacuum period".
[0053] Experiment Example 4 Experimental Methods: Samples with different phases were prepared by controlling the blending process and annealing conditions. Island structures were obtained through rapid cooling; layered structures were obtained through slow annealing (120℃, 4 hours); and bicontinuous phases were obtained by precisely controlling the BA / BT compatibility (adding 5wt% PEG). Phase region sizes were observed and statistically analyzed using TEM, and the increase in specific surface area was determined by BET nitrogen adsorption to measure changes before and after degradation. The test results are shown in Table 4.
[0054] Table 4. Effect of phase region structure on degradation performance
[0055] Results analysis: Phase size effect: The phase size of the controllable layered bicontinuous phase is only 0.8 μm, which is 75% smaller than that of the island structure. After the BA phase degrades, the BT phase loses its support, its mechanical integrity is rapidly destroyed, and its specific surface area increases by 15.2 times.
[0056] Mechanical degradation controllability: The tensile strength retention rate of the preferred sample dropped to 45% after 60 days, indicating that the material had disintegrated into fragments, but the retention rate after 30 days was 92%, proving that the strength was reliable during the service life.
[0057] Conclusion: Degradation-strength window: Phase region structure regulation achieves a balance between "strength maintenance during service life" and "rapid disintegration after disposal".
[0058] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.
Claims
1. A controllably layered distribution PBAT-based degradable lunch box material, characterized in that, It contains polybutylene adipate-terephthalate copolymer (PBAT), which is composed of aliphatic segments (BA segments) and aromatic segments (BT segments); The PBAT is a multiblock copolymer with a controllable layered distribution tendency, wherein the BA segments and BT segments are arranged in a quasi-alternating pattern, and the sequence regularity index η≥0.65, wherein η is calculated by measuring the area ratio of the carbonyl carbon chemical shift splitting peak by ¹³C-NMR, and η=Ialternating / (Ialternating+Iranical); The BA segment is composed of multiple repeating units of butylene adipate, with a number-average molecular weight Mn of 3000-8000 g / mol, and the BT segment is composed of multiple repeating units of butylene terephthalate, with a number-average molecular weight Mn of 15000-35000 g / mol. The molecular weight ratio of the BA segment to the BT segment is 1:3 to 1:5; The melt flow index of the PBAT is 3-8 g / 10 min (2.16 kg at 190℃). After melt blending and controlled heat treatment, the controllable layered PBAT-based biodegradable lunchbox material can selectively exhibit one of the following three phase structures: (a) Island structure: The BA phase is dispersed in microspheres in the BT continuous phase, with a phase region size of 0.1-1 μm; (b) Controllable layered bicontinuous phase structure: BA phase region and BT phase region are arranged alternately, and the phase region size is 0.5-2μm.
2. A controllably layered distributed PBAT based degradable lunch box material as claimed in claim 1, wherein, The product further comprises 0.3-0.8 wt% of pH-responsive microcapsules, wherein the core material of the pH-responsive microcapsules is a complex of lipase and citrate monoglyceride, and the wall material of the pH-responsive microcapsules is polylactic acid, which can rupture in an environment with a pH below 6.
5. The pH-responsive microcapsules rupture and release the core material in an acidic environment generated by the degradation of BA segments.
3. A controllably layered distributed PBAT based degradable lunch box material as claimed in claim 1, wherein, The phase structure of the PBAT is a layered bicontinuous phase, in which the BA phase region and the BT phase region are arranged alternately, and the phase region size is 0.5-2μm.
4. A controllably layered distributed PBAT based degradable lunch box material as claimed in claim 1, wherein, It further contains 5-15 wt% of a water-soluble porogen, polyethylene glycol 2000 (PEG2000), which dissolves upon contact with water to form micropores with an average pore size of 50-200 nm.
5. A controllably layered distributed PBAT based degradable lunch box material as claimed in claim 1, wherein, When further comprising 5-25 parts of bio-based filler, it also comprises 0.5-2 parts of reactive compatibilizer, which forms a graft copolymer in situ during extrusion to maintain the continuity of the PBAT phase region.
6. The method for preparing the biodegradable lunchbox material according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. Synthesis of alternating block PBAT prepolymer: Butylene adipate prepolymer (BA prepolymer, Mn=3000-8000 g / mol) and butylene terephthalate prepolymer (BT prepolymer, Mn=15000-35000 g / mol) were mixed at a molar ratio of 1:3 to 1:
5. 0.03-0.08 wt% tetrabutyl titanate catalyst was added, and the transesterification reaction was carried out at 240-250 °C and a vacuum degree of 50-100 Pa for 2-3 hours under an inert atmosphere. The vacuum treatment was used to remove reaction byproducts. This post-treatment step controlled the melt index of the PBAT copolymer to 3-8 g / 10 min (190 °C, 2.16 kg), resulting in a multi-block copolymer with a controllable layered distribution tendency, thus obtaining the PBAT copolymer. S2. Melt blending: The PBAT copolymer obtained in step S1 is melt-blended with 5-25 parts of optional bio-based filler and 5-15 wt% polyethylene glycol (PEG 2000) processing aid in a twin-screw extruder at 160-180°C, with a screw speed of 150-200 rpm and a residence time of 2-3 minutes to obtain granules, namely the biodegradable lunch box material. The PEG 2000 acts as a water-soluble pore-forming agent, which dissolves in subsequent use to form 50-200 nm micropores. After melt blending, by controlling the subsequent heat treatment process, three different phases of the biodegradable lunchbox material can be obtained: Rapid cooling: Cooling rate ≥ 50℃ / s, to obtain the biodegradable lunch box material with an island structure; Slow cooling and annealing: cooling rate ≤5℃ / s, annealing at 100-140℃ for 2-6h to obtain the biodegradable lunch box material with a controllable layered distribution of bicontinuous phases; S3. pH-responsive microcapsule loading: After the granules obtained in step S2 are thermoformed into a lunchbox semi-finished product, a pH-responsive microcapsule dispersion is sprayed or dipped onto the surface of the lunchbox, or the microcapsule dispersion is pre-coated and bonded to the surface of the granules before thermoforming, so that the pH-responsive microcapsules are loaded onto the material surface. The microcapsule loading amount is 0.3-0.8 wt%. The pH-responsive microcapsules were prepared by the following method: lipase (activity 10000-15000 U / g) and glyceryl citrate were dissolved in water at a mass ratio of 1:2-1:3 to prepare a core material solution with a solid content of 15-20%; polylactic acid (Mn=8000-12000) was dissolved in dichloromethane to prepare a wall material solution with a content of 10-12 wt%; microcapsules with a particle size of 20-50 μm and an encapsulation efficiency >85% were obtained by solvent evaporation at a wall material / core material mass ratio of 1:1-1.2:1 and a stirring speed of 800-1200 rpm.
7. A biodegradable lunchbox, characterized in that, The degradable lunch box material according to any one of claims 1-5 is made by thermoforming process. The lunch box has a wall thickness of 0.4-0.8 mm, a volume of 500-1000 mL, a tensile strength retention rate of >90% during its service life, and a degradation rate of >90% within 120 days under industrial composting conditions.
8. A biodegradable lunchbox as described in claim 7, characterized in that, The thermoforming process includes the following steps: Sheet extrusion: The granules obtained in step S2 are melted and plasticized in a single screw extruder at 160-180℃, and extruded into sheets through a coat hanger die. The sheet thickness is 0.4-0.8mm, the extrusion rate is 3-5m / min, the cooling roller temperature is 15-20℃, and the cooling rate is >50℃ / s. Vacuum forming: The sheet material is heated to above the softening point but below the melting point, i.e., the temperature range is 150-160℃, the heating time is 20-30 seconds, and it is vacuum formed into a lunch box under a vacuum degree of 0.06-0.08MPa. The mold temperature is 30-50℃, the forming time is 3-5 seconds, and the pressure is held and cooled for 10-15 seconds.