A multi-layer composite tableware with controllable degradation of time sequence and a preparation method thereof

Abstract

The application discloses a kind of time sequence controllable degradation multilayer composite tableware and preparation method thereof.The tableware includes sequentially compounded outer layer, slow degradation layer (high crystallinity PLA / PBS / PBAT, crystallinity 55-65%), intermediate layer gradient transition layer (containing reactive compatibilizer and nanocellulose), and inner layer fast degradation layer (TPS / PLA / PGA, crystallinity 15-25%).Three layers are precisely compounded by microfluidic co-extrusion technology, so that the tableware maintains excellent performance within 6-12 months shelf life, and realizes "inner layer first disintegration, outer layer follow-up degradation" time sequence controllable degradation within 60-90 days after use.The application breaks through the contradiction between shelf life and degradation rate, and can be widely applied to fast food boxes, cold drink cups, knives and forks and other disposable tableware fields.

Description

Technical Field

[0001] This invention relates to the field of bio-based material processing technology, specifically to a time-controlled degradable multilayer composite tableware and its preparation method. Background Technology

[0002] With tightening global policies on plastic pollution control, the market demand for biodegradable disposable tableware is growing rapidly. Bio-based materials such as polylactic acid (PLA) and polybutylene succinate (PBS) have become important alternatives to traditional petroleum-based plastics due to their excellent biodegradability and processability.

[0003] However, existing biodegradable tableware generally suffers from the following technical contradictions: The contradiction between shelf life and degradation rate: In existing technologies, to improve the temperature resistance and mechanical properties of PLA, it is usually modified by increasing crystallinity or adding inorganic fillers. Although high-crystallinity PLA (crystallinity > 50%) has improved temperature resistance, its degradation cycle is extended to 12-24 months, which is difficult to meet the environmental protection requirement of "rapid degradation after use"; while low-crystallinity PLA or materials with high starch content degrade quickly (1-3 months), but have a short shelf life and are prone to performance degradation during the shelf life.

[0004] Limitations of single-material performance: Pure PLA is brittle and lacks toughness; pure PBS has a slow crystallization rate and a long molding cycle; starch-based materials have poor water resistance. Although simple blending can improve a certain property, it is difficult to achieve the synergistic effect of multiple objectives such as "high temperature resistance, high strength, and rapid degradation".

[0005] The existing tableware has a single structure and function. Most of the existing tableware is homogeneous and cannot be customized according to the usage scenario (such as hot / cold food, short-term / long-term storage). It also lacks an intelligent response mechanism that "actively accelerates degradation after use".

[0006] Patent CN115927104A discloses a high-heat-resistant PLA straw, which improves temperature resistance through a three-layer co-extrusion technology. However, all three layers are PLA-based materials, have a single function, and do not involve degradation timing regulation. CN113603972B discloses a plant fiber / rigid particle / polypropylene composite material, but it belongs to a non-degradable system and does not involve multi-layer gradient structure design.

[0007] Therefore, developing a tableware that can achieve a balance between stable shelf-life performance and rapid degradation after use has become a pressing technical problem to be solved in this field. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention proposes a time-controlled degradable multilayer composite tableware and its preparation method. This achieves a balance between stable shelf-life performance and rapid degradation after use.

[0009] To achieve the above objectives, the technical solution of the present invention is implemented as follows: To achieve the above objectives, the present invention provides the following technical solution: A time-controlled degradable multilayer composite tableware, comprising an outer layer, a middle layer, and an inner layer sequentially laminated together: The outer layer is a slow-degrading layer, composed of the following components in parts by mass: Highly crystalline polylactic acid (PLA) 60-75 parts, polybutylene succinate (PBS) 15-25 parts, polybutylene terephthalate adipate (PBAT) 5-10 parts, inorganic nanofiller (nano-calcium carbonate or nano-montmorillonite, particle size 30-80nm) 3-8 parts, antioxidant 0.3-0.8 parts, lubricant 0.5-1.5 parts.

[0010] The outer layer crystallinity is controlled at 55-65%, the glass transition temperature is ≥60℃, and the degradation induction period is ≥180 days.

[0011] The inner layer is a rapidly degradable layer, composed of the following components in parts by mass: Thermoplastic starch (TPS) 40-55 parts, low-crystallinity polylactic acid (PLA) 25-35 parts, polyglycolic acid (PGA) 10-20 parts, plasticizer (glycerol or sorbitol) 5-10 parts, compatibilizer (maleic anhydride grafted PLA) 3-6 parts, degradation promoter (aliphatic polyesterase or photosensitizer) 0.5-2 parts.

[0012] The PGA in the inner layer is dispersed in a solid state, and the material is a composite structure of "PLA / TPS matrix + PGA particles".

[0013] The crystallinity of the inner layer is controlled at 15-25%, and the weight loss rate is ≥60% after 30 days under composting conditions (58 ℃, 50% humidity).

[0014] The intermediate layer is a gradient transition layer, composed of the following components in parts by mass: 40-50 parts of medium-crystallinity polylactic acid (PLA), 20-30 parts of polybutylene succinate (PBS), 15-25 parts of thermoplastic starch (TPS), 2-5 parts of reactive compatibilizer (isocyanate or epoxy), and 2-4 parts of nanocellulose.

[0015] The crystallinity of the intermediate layer is controlled at 35-45%, and the thickness is 15-25% of the total wall thickness. It forms a chemical bond and molecular chain interpenetration structure with the inner and outer layers through a reactive compatibilizer.

[0016] The three-layer structure is integrally formed by microfluidic co-extrusion technology. The thickness ratio of the outer layer, middle layer and inner layer is 25-35%: 15-25%: 40-60%, the sum of the thicknesses of the three layers is 100%, and the total thickness of the three layers is 0.5-2.0 mm.

[0017] The present invention also provides a method for preparing the above-mentioned time-controllable degradation multilayer composite tableware, comprising the following steps: (1) Premixing and granulation of raw materials for each layer Preparation of the slow-degrading layer (outer layer): High-crystallinity PLA (crystallinity ≥40%, molecular weight 100,000-150,000, D-lactic acid content <2%), PBS, and PBAT are vacuum dried at 60℃ for 4-6 hours until the moisture content is <0.01%. Inorganic nanofillers (surface-treated with silane coupling agent), antioxidants, and lubricants are added according to the formula, and the mixture is mixed in a high-speed mixer for 10-15 minutes. The mixture is then fed into a twin-screw extruder, set at a temperature of 160-180℃ and a screw speed of 200-300 rpm, and melt-extruded to granulate, obtaining the outer layer special material.

[0018] Preparation of the rapidly degradable layer (inner layer): Thermoplastic starch (TPS) is obtained by plasticizing starch (corn starch or cassava starch with a moisture content of <10%) with a plasticizer in a high-shear mixer at 120-140℃ for 10-15 minutes. Low-crystallinity PLA (crystallinity ≤20%, molecular weight 80,000-120,000, D-lactic acid content 4-8%), PGA, TPS, compatibilizer, and degradation promoter are dried at 50℃, mixed in proportion, and fed into a twin-screw extruder. The extrusion temperature is set at 160-180℃ (to avoid excessive degradation of PGA), and the screw speed is 150-250 rpm. The mixture is then melt-extruded and granulated to obtain the inner layer special material.

[0019] Gradient transition layer (intermediate layer) fabrication: After drying medium-crystallinity PLA (crystallinity 20-40%, molecular weight 90,000-130,000), PBS, and TPS, they are mixed with reactive compatibilizers and nanocellulose, added to a twin-screw extruder, set at a temperature of 150-170℃ and a screw speed of 180-280 rpm, and melt-extruded to granulate to obtain a special material for the intermediate layer.

[0020] (2) Microfluidic co-extrusion molding A three-layer co-extrusion die is used, equipped with a melt pump and an online layer thickness monitoring system. The outer, middle, and inner layer materials are separately fed into three single-screw extruders, with the following temperature gradients set:

[0021] The volumetric flow rate ratio of the three melt layers is precisely controlled by a melt pump to be (25-35):(15-25):(40-60). The melt layers converge within the die head through layered flow channels to form a three-layer melt flow. A microfluidic distributor is used to regulate the flow stability of each melt layer, ensuring that the layer thickness uniformity error is <±5%.

[0022] The melt flow is initially cooled and shaped by a sizing die (temperature 80-100℃), then rolled to the target thickness by a three-roll calender (roll temperature 60-80℃), and finally cut or thermoformed (vacuum forming / compression forming) to obtain tableware products.

[0023] (3) Post-treatment and crystallization control The molded tableware is annealed at 80-90℃ for 10-30 minutes to promote the cold crystallization of the outer PLA layer, achieving a crystallinity of 55-65%. After annealing, it is immediately cooled to room temperature to freeze the amorphous structure of the intermediate and inner layers, ensuring that the inner layer maintains a low crystallinity.

[0024] The innovative mechanism of this invention: 1. Time-controlled degradation mechanism The outer layer, a highly crystalline PLA / PBS / PBAT blend, forms a dense crystalline region and a hydrophobic interface, effectively blocking the penetration of moisture and oxygen, resulting in a degradation induction period of over 6 months. The inner TPS / PGA system contains a large number of hydrophilic hydroxyl groups and amorphous regions, which rapidly absorb water and swell in a humid and hot environment. The ester bonds of PGA undergo autocatalytic hydrolysis under the influence of trace amounts of moisture, resulting in a molecular weight decrease of over 80% within 30 days, leading to the initial disintegration of the inner layer. After the inner layer disintegrates, the outer layer loses its support, its specific surface area increases, and the degradation rate accelerates accordingly, achieving a sequential degradation process of "inner layer triggering - outer layer following".

[0025] 2. Interface Interoperability Enhancement Mechanism The intermediate layer uses a reactive compatibilizer (such as toluene diisocyanate TDI or epoxy chain extender ADR) to react with the terminal hydroxyl groups of the outer PLA layer and the hydroxyl groups of the inner TPS layer during melt co-extrusion, forming urea groups or ester bonds. At the same time, the nanocellulose of the intermediate layer acts as a physical anchor point, interpenetrating between the inner and outer matrix layers to form a dual interfacial bond of "chemical bonding + physical entanglement", with an interlayer peel strength >5 N / cm.

[0026] 3. Precise control of microfluidic layer thickness By using closed-loop control of the melt pump (accuracy ±0.5%) and a microfluidic distributor in the die head, stable laminar flow of three layers of melt with significant viscosity differences (the viscosity of the outer layer is 3-6 times that of the inner layer) is achieved, avoiding interlayer mixing or interface instability.

[0027] The beneficial effects of this invention are: (1) Overcoming the contradiction between shelf life and degradation rate This invention utilizes a gradient structural design with a "slow outer layer and fast inner layer" to ensure that tableware retains over 90% of its tensile strength within 6 months under storage conditions of 25℃ / 50%RH, meeting shelf-life requirements. After use, under composting conditions, the inner layer disintegrates within 30 days, the inner and outer layers crack within 60 days, and it completely degrades into CO2 and H2O within 90 days. In contrast, while tableware made from single-layer, highly crystalline PLA has a longer shelf life, its degradation cycle requires 180-360 days.

[0028] (2) Synergistically improve mechanical properties and temperature resistance The outer layer of highly crystalline PLA / PBS blend provides excellent temperature resistance (heat distortion temperature ≥100℃) and rigidity (flexural modulus ≥3000 MPa), allowing it to hold hot food (≤100℃) without deformation; the middle layer's nanocellulose reinforcement and interpenetrating structure ensure strong interlayer bonding, resulting in an overall impact strength >8 kJ / m². 2 It is far superior to pure PLA tableware (3-5 kJ / m³). 2 ).

[0029] (3) Reduce raw material costs The inner layer has a TPS content as high as 40-55%, and the starch price is only 1 / 5 to 1 / 8 of that of PLA. The overall raw material cost is 30-40% lower than that of pure PLA tableware. Furthermore, the outer layer can be recycled and reused after the inner layer disintegrates, further improving economic efficiency.

[0030] (4) Achieve functional customization By adjusting the thickness ratio and formula of the three layers, products with different degradation sequences can be customized: such as short-term use tableware (thickened inner layer, complete degradation in 30 days) and long-term storage containers (thickened outer layer, shelf life of 12 months, degradation 120 days after use). Detailed Implementation

[0031] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0032] For experiments not specified in this protocol, the procedures and conditions described in the literature within this field should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products. Example 1

[0033] This embodiment provides a fast food box (shelf life of 6 months, degradable after 90 days of use) and its preparation method. The fast food box has a three-layer structure. Outer layer formulation (parts by weight): High crystallinity PLA (NatureWorks 4032D), crystallinity 40%: 70 parts; PBS (Showa Denko 1020MD): 20 parts; PBAT (BASF ecoflex): 8 parts; Nano calcium carbonate (particle size 50nm, treated with KH-550): 5 parts; Antioxidant 1010: 0.5 parts; Calcium stearate: 1.0 part.

[0034] Intermediate layer formulation (parts by weight): Medium-crystallinity PLA (NatureWorks 2003D), crystallinity 25%: 45 parts; PBS (Showa Denko 1020MD): 25 parts; TPS (glycerol plasticized corn starch, glycerol content 25%): 20 parts; Toluene diisocyanate (TDI): 3 parts; Nanocellulose (diameter 10-20nm, length 500-1000nm): 3 parts.

[0035] Inner layer formula (parts by weight): TPS (same as above): 50 parts; Low crystallinity PLA (NatureWorks 4060D), crystallinity 10%: 30 parts; PGA (molecular weight 50,000): 15 parts; Glycerol: 8 parts; Maleic anhydride grafted PLA (grafting rate 1.2%): 4 parts; Aliphatic polyesterase (Novozymes Lipolase): 1 part.

[0036] The manufacturing process of the fast food box includes the following steps: (1) The raw materials for each layer are premixed and granulated according to the above formula, and dried until the moisture content is <0.05%; Granulation of the outer layer special material: High-crystallinity PLA (crystallinity 60%, molecular weight 100,000-150,000, D-lactic acid content <2%), PBS, and PBAT were vacuum dried at 60℃ for 5 hours, with a moisture content <0.01%. Inorganic nanofillers (surface-treated with silane coupling agent), antioxidants, and lubricants were added according to the formula, and mixed in a high-speed mixer for 15 minutes. The mixture was added to a twin-screw extruder, set at a temperature of 170℃ and a screw speed of 200 rpm, and melt-extruded to granulate, obtaining the outer layer special material.

[0037] Preparation of the rapidly degradable layer (inner layer): Starch (corn starch, moisture content <10%) and plasticizer glycerin are plasticized in a high-shear mixer at 130℃ for 15 minutes to obtain thermoplastic starch (TPS). Low-crystallinity PLA (crystallinity 10%, molecular weight 80,000-120,000, D-lactic acid content 4-8%), PGA, TPS, compatibilizer, and degradation promoter are dried at 50℃, mixed in proportion, and added to a twin-screw extruder. The temperature is set at 180℃ (to avoid excessive degradation of PGA), and the screw speed is 200 rpm. Melt extrusion granulation is performed to obtain the special material for the inner layer.

[0038] Gradient transition layer (intermediate layer) fabrication: Medium-crystallinity PLA (crystallinity of 25%, molecular weight of 90,000-130,000), PBS, and TPS were dried, then mixed with reactive compatibilizer and nanocellulose, and fed into a twin-screw extruder. The mixture was set at 160°C and 1220 rpm for melt extrusion granulation to obtain a special material for the intermediate layer.

[0039] (2) A three-layer co-extrusion sheet production line is adopted. A three-layer co-extrusion die is used, equipped with a melt pump and an online layer thickness monitoring system. The outer, middle, and inner layer materials are separately fed into three single-screw extruders, with the following temperature gradients set:

[0040] Melt pump control flow ratio: outer layer 30%, middle layer 20%, inner layer 50%.

[0041] The melt flows through layered channels within the die head, forming a three-layer melt flow. A microfluidic distributor is used to regulate the flow stability of each melt layer, ensuring a layer thickness uniformity error of <±5%. The die head gap is 1.5mm, the extrusion speed is 5m / min, and the melt is calendered to a 1.0mm thick sheet through a three-roll calender (upper roll 90℃, middle roll 80℃, lower roll 70℃).

[0042] The melt flow is initially cooled and shaped by a sizing die (temperature 90℃), then rolled to the target thickness by a three-roll calender (roll temperature 70℃), and finally thermoformed (vacuum forming / compression forming) to obtain the primary product of the lunch box (volume 500mL, wall thickness 0.8mm).

[0043] The molded tableware is annealed at 85℃ for 20 minutes to promote the cold crystallization of the outer PLA layer, achieving a crystallinity of 55-65%. Immediately after annealing, it is cooled to room temperature to freeze the amorphous structure of the intermediate and inner layers, ensuring that the inner layer maintains a low crystallinity. Performance testing:

[0044] Initial tensile strength: 42 MPa (longitudinal), 38 MPa (transverse) Heat distortion temperature (0.45MPa): 105℃ Interlayer peel strength: 6.2 N / cm Tensile strength retention rate after 6 months of storage at 25℃ / 50%RH: 92%; Composting degradation (58℃, 50% humidity): 30 days: Inner layer disintegrates, overall weight loss 45%. 60 days: Outer layer cracks, overall weight loss 78%. 90 days: Completely degraded, residue <2%. Example 2

[0045] This embodiment provides a cold drink cup (shelf life of 12 months, degrades after 60 days of use) and its manufacturing process. The cold drink cup is made of a three-layer structure. Outer layer formulation (parts by weight): Highly crystalline PLA (50% crystallinity): 75 parts, PBS: 18 parts, PBAT: 5 parts, Nano-montmorillonite (modified with cetyltrimethylammonium bromide): 6 parts, Antioxidant 168: 0.6 parts, EBS wax: 1.2 parts Intermediate layer formulation (parts by weight): Medium-crystallinity PLA (20% crystallinity): 50 parts, PBS: 22 parts, TPS: 18 parts, epoxy chain extender (ADR4468): 4 parts, nanocellulose: 4 parts Inner layer formula (parts by weight): TPS: 45 parts, Low-crystallinity PLA (8% crystallinity): 35 parts, PGA: 12 parts, Sorbitol: 6 parts, Maleic anhydride-grafted PLA: 5 parts, Photosensitizer (benzophenone): 0.8 parts The preparation process includes the following steps: (1) The raw materials of each layer are premixed and granulated according to the above formula, and dried to a moisture content of <0.05%; the same as the preparation process steps (1) in Example 1. (2) Microfluidic co-extrusion technology is adopted, and the flow ratio controlled by the melt pump is: 35% for the outer layer, 25% for the middle layer, and 40% for the inner layer, with a flow accuracy within ±0.5%. The layer thickness uniformity error is controlled to be less than ±5% by the microfluidic distributor; the extruder temperature is 180℃ for the outer layer, 175℃ for the middle layer, and 160℃ for the inner layer; the die gap is 1.5mm, and the extrusion speed is 5m / min. (3) The melt flow is initially cooled and shaped by a 100°C forming die, then rolled to a 0.6mm thick sheet by three-roll calendering (roller temperature 80°C), and finally thermoformed (vacuum forming / compression forming) to obtain the initial product of cold drink cups and tableware; The initial product of the cold drink cup / tableware is annealed at 90℃ for 10 minutes to promote the cold crystallization of the outer PLA layer, so that the crystallinity of the outer layer reaches 55-65% and the crystallinity of the inner layer is maintained at 15-25%. After annealing, it is immediately cooled to room temperature to obtain the final product of the cold drink cup with a wall thickness of 0.6mm.

[0046] Performance testing: Initial light transmittance (outer layer): 82% Initial tensile strength: 45 MPa; Tensile strength retention rate after 12 months of storage at 25℃ / 50%RH: 88%; Outdoor exposure (25℃, natural humidity), composting degradation (58℃, 50% humidity). 30 days: Inner layer softens, overall weight loss 52%. 60 days: Complete collapse. Example 3

[0047] This embodiment provides a disposable knife and fork (shelf life of 9 months, degradable after 75 days of use) and its preparation method, wherein the disposable knife and fork has a three-layer structure. Outer layer formulation (parts by weight): Highly crystalline PLA (60% crystallinity): 65 parts, PBS: 22 parts, PBAT: 10 parts, nano-calcium carbonate: 8 parts, antioxidant 1010: 0.4 parts, zinc stearate: 0.8 parts Intermediate layer formulation (parts by weight): Medium-crystallinity PLA (40% crystallinity): 42 parts; PBS: 28 parts; TPS: 22 parts; TDI: 2.5 parts; Nanocellulose: 2.5 parts; Inner layer formula (parts by weight): TPS: 55 parts, low crystallinity PLA (10% crystallinity): 25 parts, PGA: 18 parts, glycerol: 10 parts, maleic anhydride-grafted PLA: 3 parts, aliphatic polyesterase: 1.5 parts; Preparation process: (1) The raw materials of each layer are premixed and granulated according to the above formula, and dried to a moisture content of <0.05%; the same as the preparation process steps (1) in Example 1. (2) Microfluidic co-extrusion technology is adopted, and the flow ratio controlled by the melt pump is: 35% for the outer layer, 25% for the middle layer, and 40% for the inner layer, with a flow accuracy within ±0.5%. The layer thickness uniformity error is controlled to be less than ±5% by the microfluidic distributor; the extruder temperature is 175℃ for the outer layer, 160℃ for the middle layer, and 170℃ for the inner layer; the die gap is 1.5mm, and the extrusion speed is 5m / min. (3) The melt flow is initially cooled and shaped by a 100°C shaping die, then rolled to a 0.6mm thick sheet by three-roll calendering (roller temperature 80°C), and finally cut and hot-pressed to obtain the initial product of disposable cutlery. The initial product of disposable cutlery was annealed at 90°C for 10 minutes, and then immediately cooled to room temperature to obtain a final product with a wall thickness of 0.6 mm.

[0048] Performance testing: Bending strength: 78 MPa; Notched impact strength: 9.5 kJ / m 2 ; Hot water resistance (100℃, 30 minutes): No deformation, no leakage; Compost degradation in 75 days: complete degradation. Comparative Example 1

[0049] This comparative example provides a non-layered blended tableware product (similar to CN113603972B), prepared by the following method: High-crystallinity PLA (40% crystallinity, 70 parts), PBS (25 parts), and PBAT (5 parts) were blended and granulated. The granulation process was the same as that of the outer layer component in Example 1. The extrusion process was the same as that of the outer layer component in Example 1. The mixture was then injection molded into a lunch box (0.8 mm wall thickness), using the same tableware processing process as in Example 1.

[0050] Initial tensile strength: 48 MPa (higher than Example 1); Heat distortion temperature: 110℃ (higher than Example 1); Performance retention rate after 12 months of storage: 95%; Composting degradation after 180 days: only 35% weight loss, but serious residue. Comparative Example 2

[0051] This comparative example provides a simple blend of starch / PLA tableware: PLA (40% crystallinity, 50 parts), starch (40 parts), glycerol (8 parts), and compatibilizer (2 parts) were blended, granulated, and injection molded. The preparation process was the same as that of Comparative Example 1.

[0052] Performance comparison: Initial tensile strength: 22 MPa (significantly lower than Example 1) After 3 months of storage, the tensile strength decreased to 15 MPa (insufficient shelf life). Compost degradation in 30 days: Complete disintegration (degradation too fast). Comparative Example 3

[0053] This comparative example provides a three-layer co-extruded tableware with no gradient design (similar crystallinity of each layer). The outer, middle and inner layers all use the same formula (PLA / PBS / TPS=60 / 20 / 20), and the crystallinity of each layer is 40%.

[0054] The preparation process is the same as that of Comparative Example 1.

[0055] Performance testing: Interlayer peel strength: 2.1 N / cm (far lower than in Example 1, due to lack of viscosity gradient and reactive compatibilizer). The overall strength decreased by 40% after 6 months of storage (due to rapid moisture penetration). After 60 days of compost degradation: the overall weight loss was 55%, with no "inner layer disintegration" phenomenon. Comparative Example 4

[0056] This comparative example provides a lunch box in which no reactive compatibilizer or nanocellulose is added to the middle layer; the rest of the formulation and process are the same as in Example 1.

[0057] Performance testing: The interlayer peel strength is low (<3 N / cm), and it is easy to delaminate during use, which affects the overall performance. The middle layer cannot effectively buffer the stress at the interface between the inner and outer layers, which affects the stability of the degradation sequence.

[0058] This demonstrates that the synergistic effect of reactive compatibilizers and nanocellulose is a necessary means to achieve strong interlayer bonding and ensure stable temporal degradation. Comparative Example 5

[0059] This comparative example provides a lunchbox that retains the same outer and middle layers as in Example 1; the inner layer is changed to a "TPS / low-crystallinity PLA" system, which does not contain PGA or degradation promoters; the crystallinity is still controlled at 15-25%. The remaining formulation and process steps are the same as in Example 1.

[0060] Performance testing: There was no significant difference in performance during the storage period; After 30 days of compost degradation, the inner layer did not disintegrate, and the overall weight loss was less than 20%. The sequential degradation effect of "inner layer prior disintegration" could not be achieved. This demonstrates that the introduction of PGA is a key technical feature for achieving rapid hydrolysis of the inner layer and triggering sequential degradation. Comparative Example 6

[0061] This comparative example provides a lunch box that uses the exact same material system and layer thickness ratio as Example 1; The difference in the preparation process compared to Example 1 is that a conventional three-layer co-extrusion die is used, but there is no melt pump closed-loop control or microfluidic distributor.

[0062] Poor uniformity of layer thickness, with an error >±15%; due to the much higher viscosity of the outer layer than the inner layer, interlayer mixing or interface curling is prone to occur; the degradation sequence is unstable, with large batch-to-batch differences. This demonstrates that microfluidic co-extrusion is a key process for achieving stable molding of high viscosity difference melts and ensuring structural consistency.

[0063] In summary, Examples 1-3 all achieved the goal of "stable performance during shelf life + rapid degradation after use", with tensile strength retention rate >88% within 6-12 months and complete degradation within 60-90 days after use.

[0064] Although Comparative Example 1 has excellent mechanical properties and temperature resistance, its degradation cycle is too long (>180 days), which does not meet the environmental protection intention of "degradable".

[0065] Although Comparative Example 2 degrades quickly, it has a short shelf life and poor mechanical properties, which cannot meet the requirements for commercialization.

[0066] Comparative Example 3 demonstrates that a three-layer structure without a “crystallization gradient” and a “reactive compatibilizer” design cannot achieve time-controlled degradation, and the interlayer bonding is weak.

[0067] Comparative Example 4 demonstrates that the synergistic effect of reactive compatibilizers and nanocellulose is a necessary means to achieve strong interlayer bonding and ensure stable time-series degradation.

[0068] Comparative Example 5 demonstrates that the introduction of PGA is a key technical feature for achieving rapid hydrolysis of the inner layer and triggering sequential degradation.

[0069] Comparative Example 6 demonstrates that microfluidic co-extrusion is a key process for achieving stable molding of high viscosity difference melts and ensuring structural consistency.

[0070] The above results indicate that the “slow outside, fast inside” gradient structure, reactive compatibilizer interface enhancement, and microfluidic co-extrusion process described in this invention are three essential technical features for achieving time-controlled degradation, and none of them can be omitted.

[0071] Finally, 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. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A multi-layered composite tableware with time-controlled degradation, characterized in that, It includes an outer layer, a middle layer, and an inner layer that are sequentially laminated: The outer layer is a slow-degradable layer, and its components include highly crystalline polylactic acid, polybutylene succinate, and polybutylene adipate. The inner layer is a fast-degradable layer, and its components include thermoplastic starch, low-crystallinity polylactic acid, and polyglycolic acid; The intermediate layer is a gradient transition layer, and its components include polylactic acid with moderate crystallinity, polybutylene succinate, and thermoplastic starch. The outer layer has a crystallinity of 55-65%, the middle layer has a crystallinity of 35-45%, and the inner layer has a crystallinity of 15-25%; the thickness ratio of the outer layer, middle layer, and inner layer is 25-35%: 15-25%: 40-60%, and the sum of the thicknesses of the three layers is 100%.

2. A multi-layered composite tableware with time-controllable degradation, characterized in that, The tensile strength retention rate of the outer layer after being stored at 25°C and 50% relative humidity for 6 months is no less than 90%. The inner layer loses no less than 60% of its weight within 30 days under composting conditions of 58°C and 50% humidity. The intermediate layer is chemically bonded to the outer and inner layers through a reactive compatibilizer; The tableware completely degrades within 60-90 days under composting conditions; Alternatively, the interlayer peel strength between the outer layer and the middle layer, and between the middle layer and the inner layer, is ≥5 N / cm.

3. The time-controlled degradable multilayer composite tableware according to claim 1, characterized in that: The mass ratio of highly crystalline polylactic acid, polybutylene succinate, and polybutylene adipate in the outer layer is 12-15:3-5:1-2. The mass ratio of thermoplastic starch, low-crystallinity polylactic acid, and polyglycolic acid in the inner layer is 8-11:5-7:2-4. The intermediate layer comprises polylactic acid with moderate crystallinity, polybutylene succinate, and thermoplastic starch in a mass ratio of 8-10:4-6:3-5.

4. The time-controlled degradable multilayer composite tableware according to claim 1, characterized in that: The outer layer is composed of the following components in parts by weight: 60-75 parts of highly crystalline polylactic acid, 15-25 parts of polybutylene succinate, 5-10 parts of polybutylene terephthalate-adipate, 3-8 parts of inorganic nanofiller, 0.3-0.8 parts of antioxidant, and 0.5-1.5 parts of lubricant; the inorganic nanofiller is nano-calcium carbonate or nano-montmorillonite surface-treated with silane coupling agent, with a particle size of 30-80 nm.

5. The time-controlled degradable multilayer composite tableware according to claim 1, characterized in that: The inner layer is composed of the following components in parts by weight: 40-55 parts thermoplastic starch, 25-35 parts low-crystallinity polylactic acid, 10-20 parts polyglycolic acid, 5-10 parts plasticizer, 3-6 parts compatibilizer, and 0.5-2 parts degradation promoter; wherein the plasticizer is glycerol or sorbitol, the degradation promoter is aliphatic polyesterase or photosensitizer, and the compatibilizer is maleic anhydride-grafted PLA.

6. The time-controlled degradable multilayer composite tableware according to claim 1, characterized in that: The intermediate layer is composed of the following components by weight: 40-50 parts of moderately crystalline polylactic acid, 20-30 parts of polybutylene succinate, 15-25 parts of thermoplastic starch, 2-5 parts of reactive compatibilizer, and 2-4 parts of nanocellulose; the reactive compatibilizer is an isocyanate or epoxy compound, and the nanocellulose has a diameter of 10-20 nm and a length of 500-1000 nm.

7. The method for preparing the time-controlled degradable multilayer composite tableware according to any one of claims 1-6, characterized in that, Includes the following steps: (1) Weigh the raw materials for the outer layer, middle layer and inner layer respectively, dry them and mix them evenly, then extrude and granulate them for later use; (2) Using microfluidic co-extrusion technology, the three-layer melt is added to three single-screw extruders in a volume ratio of (25-35):(15-25):(40-60). The flow rate is controlled within ±0.5% by the melt pump closed loop control, and the layer thickness uniformity error is controlled within ±5% by the microfluidic distributor. (3) The tableware products are obtained by shaping, calendering, cutting or thermoforming and annealing.

8. The method for preparing the time-controlled degradable multilayer composite tableware according to claim 7, characterized in that, The extrusion temperatures of the three-layer melt in step (2) are: outer layer 175-185℃, middle layer 160-175℃, and inner layer 160-180℃.

9. The method for preparing the time-controllable degradable multilayer composite tableware according to claim 7, characterized in that, The annealing temperature in step (3) is 80-90℃ and the time is 10-30min.

10. The time-controlled degradable multilayer composite tableware according to claim 1, characterized in that, The tableware includes fast food containers, cold drink cups, and cutlery.

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