A self-catalytic degradable PLA composite material and a preparation method thereof

Abstract

This application discloses a self-catalytically degradable PLA composite material and its preparation method. The PLA composite material comprises the following raw materials in parts by weight: 100 parts polylactic acid, 10-20 parts modified ethylene-acrylate-glycidyl methacrylate copolymer, and 1-3 parts catalytic degradation agent; wherein the modified ethylene-acrylate-glycidyl methacrylate copolymer contains cyclodextrin grafted into the glycidyl methacrylate segments. This application effectively solves the technical problems of insufficient interfacial compatibility between existing polylactic acid toughening systems and polylactic acid substrates, and the resulting strength loss during toughening.

Description

Technical Field

[0001] This application relates to the field of polyester biodegradable materials, and in particular to a self-catalytically degradable PLA composite material and its preparation method. Background Technology

[0002] Polylactic acid (PLA) is a thermoplastic polyester made from renewable plant resources with good biodegradability. In recent years, it has gained widespread attention and application in the field of disposable products such as food packaging, cosmetic containers, and agricultural mulch films. Compared with traditional petroleum-based plastics such as polyethylene and polypropylene, PLA products can decompose into carbon dioxide and water under industrial composting conditions after use and disposal, thus reducing the long-term burden of plastic waste on the ecological environment from the source.

[0003] However, the high rigidity of PLA molecular chains and its inherent brittleness severely limit its further application in the packaging field. Pure PLA typically has an elongation at break of less than 10% and low notched impact strength. Films, sheets, or containers made from PLA are highly susceptible to cracking and breakage under mechanical loads such as drops and bending, failing to meet the basic toughness requirements of packaging materials. To overcome this performance shortcoming, the industry commonly uses the addition of elastomer toughening agents to improve the flexibility and impact resistance of PLA. Commonly used toughening agents include ethylene-acrylate copolymers, ethylene-octene copolymers, thermoplastic polyurethanes, and polycaprolactone. Although the introduction of elastomers can effectively absorb impact energy and alleviate the brittle fracture tendency of PLA, most elastomers are non-polar or weakly polar materials with poor compatibility with the polar polyester matrix PLA. Simple blending results in weak interfacial bonding between the two phases, and the elastomer's dispersion in the PLA matrix is ​​not ideal, leading to a significant reduction in the toughening effect.

[0004] To improve the compatibility between elastomers and PLA substrates, existing technologies often employ methods such as grafting polar segments or adding reactive compatibilizers. For example, functional groups such as maleic anhydride and glycidyl methacrylate are grafted onto the elastomer molecular chain, allowing them to undergo in-situ chemical reactions with the terminal hydroxyl or carboxyl groups of PLA during melt processing, thereby enhancing the interfacial bonding between the two phases. However, the compatibilization effect of these methods still has significant limitations. On the one hand, the grafting rate of reactive groups is often limited, making it difficult to form a sufficiently continuous chemically bonded interfacial layer in the toughened PLA system. On the other hand, to achieve sufficient interfacial reactions, a high amount of toughening agent is usually required, but excessive elastomer can have a significant negative impact on the tensile strength and rigidity of the composite material, sacrificing the mechanical support properties required during use while improving toughness. Summary of the Invention

[0005] This application aims to solve the technical problems of insufficient interfacial compatibility in existing PLA toughening systems, and the resulting loss of strength during toughening.

[0006] In a first aspect, this application provides a self-catalytically degradable PLA composite material, characterized in that it comprises the following raw materials in parts by weight: 100 parts of polylactic acid, 10-20 parts of modified ethylene-acrylate-glycidyl methacrylate copolymer, and 1-3 parts of catalytic degradation agent; wherein cyclodextrin is grafted into the glycidyl methacrylate segment of the modified ethylene-acrylate-glycidyl methacrylate copolymer.

[0007] In any of the above technical solutions, the content of glycidyl methacrylate in the modified ethylene-acrylate-glycidyl methacrylate copolymer is 5-10 wt%.

[0008] In any of the above technical solutions, the modified ethylene-acrylate-glycidyl methacrylate copolymer is obtained by melt grafting of ethylene-acrylate-glycidyl methacrylate copolymer and cyclodextrin, with a mass ratio of 100:3 to 10.

[0009] In any of the above technical solutions, the temperature of the molten graft (molten zone) is 160-190°C.

[0010] In any of the above technical solutions, the raw material for melt grafting further includes a methacryloyloxysilane coupling agent, and the mass ratio of the ethylene-acrylate-glycidyl methacrylate copolymer to the methacryloyloxysilane coupling agent is 100:0.5-2.

[0011] Preferably, the methacryloyloxysilane coupling agent is a methacryloyloxypropyltrimethoxysilane coupling agent and / or a methacryloyloxypropyltriethoxysilane coupling agent.

[0012] The ethylene-acrylate-glycidyl methacrylate copolymer used in this application is a reactive elastomer. The epoxy groups in its molecular chain can undergo ring-opening reactions with the terminal carboxyl or hydroxyl groups of PLA during melt processing, forming a chemically bonded interfacial layer. This is its core advantage compared to non-reactive elastomers. However, relying solely on end-group coupling makes it difficult to form a continuous interfacial bond network between the elastomer and the substrate, limiting toughening efficiency. Furthermore, with increasing elastomer content, the tensile strength and stiffness of the composite material often decrease significantly.

[0013] This application utilizes the ring-opening reaction between the epoxy groups on the ethylene-acrylate-glycidyl methacrylate copolymer and the hydroxyl groups on the surface of cyclodextrin to graft cyclodextrin molecules into the copolymer chain segments via chemical bonds, fundamentally improving the interfacial bonding between the elastomer and the PLA substrate. Specifically, cyclodextrin acts as a heterogeneous nucleation site, and its unique ring-shaped cavity structure provides a regular template for the PLA molecular chains. During melting and cooling, it can induce the PLA molecular chains to stack orderly on its surface, forming an interfacial crystalline layer. This transforms the interfacial bonding from a point-like connection of single end-group reactions to a continuous planar anchoring, significantly enhancing the stress transfer efficiency between the elastomer and the substrate. The enhanced interfacial bonding can more effectively transfer the load from the PLA matrix to the elastomer dispersion phase, improving its impact resistance. At the same time, the presence of the interfacial crystalline layer itself has a positive effect on the rigidity and strength of the material, effectively compensating for the strength loss caused by the introduction of the elastomer. This application significantly improves the toughness of the material while effectively controlling the decrease in tensile strength, achieving a better balance between toughness and rigidity.

[0014] Furthermore, due to the regular hydrophilic cavities within cyclodextrin molecules, when grafted onto the interface between the elastomer and PLA, it effectively constructs ordered hydrophilic channels at the hydrophobic interface. During composting degradation, these channels provide directional transport pathways for water molecules to penetrate the material, allowing them to more easily act on the PLA ester bonds and initiate hydrolysis, thus helping to shorten the degradation induction period. However, the hydrophilic effect of cyclodextrin is mainly concentrated in the interfacial region and does not lead to a significant decrease in the overall mechanical properties of the material. The added catalytic degradation agent can further catalyze hydrolysis with the help of interfacial water molecules, accelerating ester bond breakage. The synergistic effect of both effectively improves the degradation rate of PLA composites after disposal.

[0015] In any of the above technical solutions, the cyclodextrin is β-cyclodextrin.

[0016] This application preferably uses β-cyclodextrin, which exhibits superior overall performance in nucleation-induced crystallization, hydrophilic channel construction, and odor adsorption.

[0017] In any of the above technical solutions, the polylactic acid is poly-L-lactic acid, poly-D-lactic acid, or a blend of the two, and the melt index of the polylactic acid is 5-30 g / 10 min (210℃, 2.16 kg).

[0018] In any of the above technical solutions, the acrylate in the ethylene-acrylate-glycidyl methacrylate copolymer is selected from one or more of methyl acrylate, ethyl acrylate, and butyl acrylate.

[0019] In any of the above technical solutions, the catalytic degradation agent is selected from one or more of iron stearate, zinc stearate, magnesium stearate, zinc oxide, and magnesium oxide.

[0020] In any of the above technical solutions, the PLA composite material further includes 0.1 to 1 part of an antioxidant, the antioxidant being selected from at least one of hindered phenolic antioxidant 1010 and phosphite antioxidant 168.

[0021] In a second aspect, this application provides a method for preparing the PLA composite material described in any of the first aspects, comprising: melt-blending dried polylactic acid, modified ethylene-acrylate-glycidyl methacrylate copolymer, and a catalytic degradation agent, and obtaining the composite material by extrusion granulation or direct molding.

[0022] In summary, this application has the following beneficial effects: This application presents a modified elastomer with toughening, interfacial reinforcement, and hydrophilicity regulation functions by chemically grafting cyclodextrin onto the molecular chain of an ethylene-acrylate-glycidyl methacrylate copolymer. During melt blending with polylactic acid, the retained epoxy groups of this modified copolymer can undergo in-situ chemical reactions with the substrate, while the grafted cyclodextrin forms a dense crystalline transition layer at the elastomer-substrate interface through epitaxial crystallization, significantly enhancing interfacial bonding and effectively improving the impact toughness of the composite material. Simultaneously, the reinforcing effect of the interfacial crystalline layer effectively compensates for the tensile strength loss caused by the introduction of the elastomer. More importantly, the ordered hydrophilic channels constructed by the cyclodextrin molecules at the interface provide a pathway for directional water penetration, producing a significant synergistic effect with the added catalytic degradation agent. This enables the composite material to possess the ability to autocatalytically accelerate degradation after disposal, while maintaining its mechanical properties during its service life. Detailed Implementation

[0023] Preparation Example Preparation Example 1: Modified ethylene-acrylate-glycidyl methacrylate copolymer, the preparation steps are as follows: Take ethylene-acrylate-glycidyl methacrylate copolymer (brand name LOTADER) ®AX8900, from Arkema, France, contains 1000g of glycidyl methacrylate (8wt%, melt index 6g / 10min (190℃ / 2.16kg)) and 60g of β-cyclodextrin (CAS No. 7585-39-9). These components are dried in a vacuum oven at 80℃~90℃ for 8 hours, then sealed and cooled before being transferred to a high-speed mixer. 12.5g of methacryloxypropyltrimethoxysilane is added, and the mixture is mixed at 800r / min for 5 minutes at room temperature to obtain a homogeneous premix. The premix is ​​then fed uniformly into the main feed port of a co-rotating twin-screw extruder using a precision metering feeder. The extruder screw diameter is 35mm, and the length-to-diameter ratio is 48:1. The temperatures of each section from the feeding zone to the die are set sequentially as follows: feeding zone 135℃, melting zone 165℃, homogenization zone 180℃, and extrusion zone 175℃. The screw speed is 120r / min. The extruded molten strip is cooled in a water tank and then cut into pellets by a pelletizer. The pellets are collected and vacuum dried at 60°C for 6 hours to obtain the modified ethylene-acrylate-glycidyl methacrylate copolymer.

[0024] Preparation Example 2, modified ethylene-acrylate-glycidyl methacrylate copolymer, the preparation steps are as follows: Take ethylene-acrylate-glycidyl methacrylate copolymer (brand name LOTADER) ® AX8840, from Arkema, France, contains 1000g of glycidyl methacrylate (8wt%, melt index 5g / 10min (190℃ / 2.16kg)) and 33g of β-cyclodextrin (CAS No. 7585-39-9). These components are dried in a vacuum oven at 80℃~90℃ for 8 hours, then sealed and cooled before being transferred to a high-speed mixer. 5g of methacryloxypropyltrimethoxysilane is added, and the mixture is mixed at 800r / min for 5 minutes at room temperature to obtain a homogeneous premix. The premix is ​​then fed uniformly into the main feed port of a co-rotating twin-screw extruder using a precision metering feeder. The extruder screw diameter is 35mm, and the length-to-diameter ratio is 48:1. The temperatures of each section from the feeding zone to the die are set sequentially as follows: feeding zone 140℃, melting zone 170℃, homogenization zone 185℃, and extrusion zone 180℃. The screw speed is 100r / min. The extruded molten strip is cooled in a water tank and then cut into pellets by a pelletizer. The pellets are collected and vacuum dried at 60°C for 6 hours to obtain the modified ethylene-acrylate-glycidyl methacrylate copolymer.

[0025] Preparation Example 3, modified ethylene-acrylate-glycidyl methacrylate copolymer, the preparation steps are as follows: Take ethylene-acrylate-glycidyl methacrylate copolymer (brand name LOTADER) ®AX8900, from Arkema, France, contains 1000g of glycidyl methacrylate (8wt%, melt index 6g / 10min (190℃ / 2.16kg)) and 95g of β-cyclodextrin (CAS No. 7585-39-9). These components are dried in a vacuum oven at 80℃~90℃ for 8 hours, then sealed and cooled before being transferred to a high-speed mixer. 20g of methacryloxypropyltrimethoxysilane is added, and the mixture is stirred at 800r / min for 5 minutes at room temperature to obtain a homogeneous premix. The premix is ​​then fed uniformly into the main feed port of a co-rotating twin-screw extruder using a precision metering feeder. The extruder screw diameter is 35mm, and the length-to-diameter ratio is 48:1. The temperatures of each section from the feeding zone to the die are set sequentially as follows: feeding zone 130℃, melting zone 160℃, homogenization zone 175℃, and extrusion zone 170℃. The screw speed is 100r / min. The extruded molten strip is cooled in a water tank and then cut into pellets by a pelletizer. The pellets are collected and vacuum dried at 60°C for 6 hours to obtain the modified ethylene-acrylate-glycidyl methacrylate copolymer.

[0026] Preparation Example 4, a modified ethylene-acrylate-glycidyl methacrylate copolymer, differs from Preparation Example 1 in that an equal amount of α-cyclodextrin (CAS No. 10016-20-3) is used to replace β-cyclodextrin (CAS No. 7585-39-9).

[0027] Preparation Example 5, a modified ethylene-acrylate-glycidyl methacrylate copolymer, differs from Preparation Example 1 in that the amount of β-cyclodextrin used is 20g.

[0028] Preparation Example 6, a modified ethylene-acrylate-glycidyl methacrylate copolymer, differs from Preparation Example 1 in that the amount of β-cyclodextrin used is 120g.

[0029] Example Example 1: A self-catalytically degradable PLA composite material was prepared according to the following steps: 1000g of polylactic acid resin (brand name Ingeo™ 4032D, NatureWorks, USA, melt index 7g / 10min (210℃ / 2.16kg)), 150g of modified ethylene-acrylate-glycidyl methacrylate copolymer (prepared in Preparation Example 1), 15g of zinc stearate, and 5g of antioxidant (antioxidant 1010 and 168 in a 1:1 mass ratio) were added to a high-speed mixer and mixed at 600r / min for 5 minutes at room temperature to obtain a uniform premix. The premixed material is fed into the main feed port of a co-rotating twin-screw extruder at a uniform speed through a precision metering feeder. The extruder screw diameter is 35mm, the length-to-diameter ratio is 48:1, and the temperatures of each section are set to 155℃, 170℃, 185℃, and 190℃ respectively, with the die head at 185℃. The screw speed is 120r / min. The extruded molten strip is cooled in a water tank and then cut into pellets by a pelletizer. The pellets are collected and vacuum dried at 60℃ for 6 hours to obtain the self-catalytically degradable PLA composite material.

[0030] Example 2: A self-catalytically degradable PLA composite material was prepared according to the following steps: 1000g of polylactic acid resin (brand name Ingeo™ 3052D, NatureWorks, USA, melt index 14g / 10min (210℃ / 2.16kg)), 105g of modified ethylene-acrylate-glycidyl methacrylate copolymer (prepared in Preparation Example 2), 10g of catalytic degradation agent (ferric stearate and zinc stearate in a 1:1 mass ratio), and 3g of antioxidant (antioxidant 1010 and 168 in a 1:1 mass ratio) were added to a high-speed mixer and mixed at 500r / min for 5 minutes at room temperature to obtain a uniform premix. The premixed material is fed into the main feed port of a co-rotating twin-screw extruder at a uniform speed through a precision metering feeder. The extruder screw diameter is 35mm, the length-to-diameter ratio is 48:1, and the temperatures of each section are set to 150℃, 165℃, 180℃, and 185℃ respectively, with the die head at 180℃. The screw speed is 120r / min. The extruded molten strip is cooled in a water tank and then cut into pellets by a pelletizer. The pellets are collected and vacuum dried at 60℃ for 6 hours to obtain the self-catalytically degradable PLA composite material.

[0031] Example 3: A self-catalytically degradable PLA composite material was prepared according to the following steps: 1000g of polylactic acid resin (brand name Ingeo™ 3052D, NatureWorks, USA, melt index 14g / 10min (210℃ / 2.16kg)), 192g of modified ethylene-acrylate-glycidyl methacrylate copolymer (prepared in Preparation Example 3), 25g of catalytic degradation agent (ferric stearate and zinc stearate in a mass ratio of 2:3), and 8g of antioxidant (antioxidant 1010 and 168 in a mass ratio of 1:1) were added to a high-speed mixer and mixed at 800r / min for 5 minutes at room temperature to obtain a uniform premix. The premixed material is fed into the main feed port of a co-rotating twin-screw extruder at a uniform speed through a precision metering feeder. The extruder screw diameter is 35mm, the length-to-diameter ratio is 48:1, and the temperatures of each section are set to 150℃, 165℃, 180℃, and 185℃ respectively, with the die head at 180℃. The screw speed is 120r / min. The extruded molten strip is cooled in a water tank and then cut into pellets by a pelletizer. The pellets are collected and vacuum dried at 60℃ for 6 hours to obtain the self-catalytically degradable PLA composite material.

[0032] Example 4, a self-catalytically degradable PLA composite material, differs from Example 1 in that an equal amount of the modified ethylene-acrylate-glycidyl methacrylate copolymer prepared in Example 4 is used instead of the modified ethylene-acrylate-glycidyl methacrylate copolymer prepared in Example 1.

[0033] Example 5, a self-catalytically degradable PLA composite material, differs from Example 1 in that an equal amount of the modified ethylene-acrylate-glycidyl methacrylate copolymer prepared in Example 5 is used instead of the modified ethylene-acrylate-glycidyl methacrylate copolymer prepared in Example 1.

[0034] Example 6, a self-catalytically degradable PLA composite material, differs from Example 1 in that an equal amount of the modified ethylene-acrylate-glycidyl methacrylate copolymer prepared in Example 6 is used instead of the modified ethylene-acrylate-glycidyl methacrylate copolymer prepared in Example 1.

[0035] Comparative Example Comparative Example 1, a self-catalytically degradable PLA composite material, differs from Example 1 in that it uses an equal amount of unmodified ethylene-acrylate-glycidyl methacrylate copolymer (brand name LOTADER). ® AX8900, Arkema, France, wherein the content of glycidyl methacrylate is 8 wt% and the melt index is 6 g / 10 min (190℃ / 2.16 kg)) replaces the modified ethylene-acrylate-glycidyl methacrylate copolymer prepared in Example 1.

[0036] Comparative Example 2, a self-catalytically degradable PLA composite material, differs from Example 1 in that zinc stearate (catalytic degradation agent) was not added.

[0037] Performance testing Experiment 1: Tensile property test Specimen Preparation: This test was conducted in accordance with GB / T 1040.1-2018 "Determination of Tensile Properties of Plastics - Part 1: General Rules" and GB / T 1040.2-2022 "Determination of Tensile Properties of Plastics - Part 2: Test Conditions for Molded and Extruded Plastics". An injection molding machine (three barrel temperatures of 165℃, 180℃, and 190℃ respectively, and a mold temperature of 25℃) was used to injection mold the PLA composite granules obtained in each example and comparative example into Type 1A multi-purpose standard tensile specimens. The total specimen length was 150 mm, the width of the narrow parallel section was 10 mm, the thickness was 4 mm, and the gauge length was 50 mm. Five qualified specimens were prepared for each formulation. Before testing, the specimens were conditioned for 24 hours at 23±2℃ and 50±10% relative humidity.

[0038] Test Procedure: During the tensile test, number the conditioned specimens and clamp them sequentially onto the pneumatic fixtures of the universal testing machine. The initial clamping distance is 115 mm, and the loading speed is set to 5 mm / min. Apply a uniform tensile load along the long axis of the specimen until it breaks. Record the maximum tensile stress during the test as the tensile strength (MPa) of the material. Simultaneously, measure the elongation of the specimen's gauge length using an extensometer (50 mm) to calculate the elongation at break. Use the arithmetic mean of all valid specimens in each group as the representative values ​​for the tensile strength and elongation at break of that group.

[0039] Experiment 2: Impact Strength Test Sample Preparation: This test was conducted in accordance with GB / T 1843-2008 "Determination of Impact Strength of Plastic Cantilever Beams". An injection molding machine (three barrel temperatures of 165℃, 180℃, and 190℃ respectively, and mold temperature of 25℃) was used to injection mold the PLA composite material granules obtained in each example and comparative example into long strips with a length of 80mm, a width of 10mm, and a thickness of 4mm. A standard type A notch was machined into the center of each sample, with a notch root radius of 0.25mm, a notch width of 8mm, and the notch face perpendicular to the long axis of the sample. Ten qualified samples were prepared for each formulation. Before testing, the samples were conditioned for 24 hours under standard environmental conditions of 23±2℃ and relative humidity of 50±10%. During the impact test, the conditioned notched samples were stably clamped onto the fixture of the cantilever beam (Izod) impact testing machine, with the back of the notch facing the impact edge of the pendulum, and the center plane of the notch flush with the top of the fixture and at the center of the pendulum impact. A pendulum of appropriate energy level (nominal energy 2.75 J) was selected based on the expected impact strength of the material, with an impact velocity of 3.5 ± 0.1 m / s. An instantaneous impact load was applied at an ambient temperature of 23℃, causing the specimen to fracture along the notch root, and the energy absorbed during fracture was recorded. The cantilever beam notched impact strength (kJ / m²) was calculated by dividing the absorbed energy by the notch width (8 mm), and the arithmetic mean of at least 10 valid specimens in each group was used as the representative value for that group.

[0040] Experiment 3: Disintegration Rate Test This experiment was conducted in accordance with ISO 20200:2015, "Determination of the degree of disintegration of plastic materials under simulated composting conditions in laboratory-scale tests". The PLA composite material granules obtained in each example and comparative example were molded into sheets with a thickness of 2.5 ± 0.2 mm, and then cut into square specimens of approximately 25 mm × 25 mm. The composting medium should preferably be commercial organic compost or a synthetic solid compost matrix prepared according to the formulation in Table 1 of ISO 20200, with its moisture content adjusted to 50%–60% according to the standard. Each specimen was numbered and placed into a nylon mesh bag (approximately 1 mm × 1 mm pore size), with approximately 20 g of each formulation specimen inside the bag. The bag opening was sealed with a heat-resistant plastic cable tie. After loosening and homogenizing the pre-prepared compost substrate with a steel shovel, it is layered approximately 50 mm thick in an opaque, heat-dissipating reaction vessel with a volume of at least 6 L. The mesh bag containing the sample is then laid flat and buried in the middle of the compost substrate in the reactor, ensuring full and uniform contact between the sample and the substrate. Small holes of appropriate diameter are made in the reactor lid to facilitate gas exchange and exhaust. The reactor is placed in a constant temperature incubator at 58±2℃. The sample is weighed regularly, and moisture lost through evaporation is replenished to maintain compost humidity. The reactor is opened and the compost is turned every 7 days to ensure aerobic conditions. On the 90th day and the end of the test (180 days), the sample mesh bag is removed, and the surface of the sample is cleaned with a fine brush under running water to remove any remaining compost. All residues are collected and transferred to a standard stainless steel test sieve with a diameter of 200 mm and an aperture of 2 mm. The sieve is then rinsed again with a gentle stream of water to complete the final separation. Subsequently, all residues trapped on the sieve (i.e., undisintegrated fragments >2 mm in size) were transferred nondestructively to pre-weighed clean petri dishes or weighing boats, dried to constant weight in a forced-air oven at approximately 40°C, then cooled to room temperature in a desiccator, and their total dry weight M1 was accurately weighed on an analytical balance. The disintegration rate (%) of each node was calculated by comparing it with the initial mass M0 of the sample: Disintegration rate (%) = [(M0-M1) / M0] × 100%. It should be noted that non-degradable ethylene segments are released as particulate matter (<2 mm in size) during PLA hydrolysis, resulting in a higher disintegration rate measured by the above sieving method.

[0041] Table 1. Performance Test Results

[0042] Analysis of experimental results: Compared to Example 1, Example 4 uses α-CD instead of β-CD for grafting. The mechanical properties of both are similar, but the 90-day disintegration rate is lower, indicating that although both can be used as heterogeneous nucleating agents, their efficiency in constructing hydrophilic channels is not as good as β-CD, resulting in a longer catalytic hydrolysis cycle for the composite material.

[0043] Compared to Example 1, Example 5 showed a significant decrease in tensile properties, impact strength, and 90-day disintegration rate due to excessively low β-CD content. This may be because insufficient β-CD grafting leads to a low density of interfacial nucleation sites, resulting in reduced continuity of the formed interfacial crystalline layer and deteriorating the effectiveness of interfacial strengthening and degradation promotion.

[0044] Compared to Example 1, Example 6, with its excessively high β-CD content, showed a significant increase in tensile strength, but a marked deterioration in elongation at break and impact strength. This may be because while an excessively high β-CD grafting amount provides denser nucleation sites and promotes the formation of the interfacial crystalline layer, excessive crystallinity can actually increase the material's brittleness, negatively impacting its toughness.

[0045] Compared to Example 1, Comparative Example 1 used an equal amount of ethylene-methyl acrylate-glycidyl methacrylate copolymer without grafted cyclodextrin. Its tensile strength, elongation at break, impact strength, and disintegration rate were all significantly reduced. This is because the elastomer without grafted cyclodextrin only bonds to the polylactic acid interface through a small amount of coupling reaction between epoxy groups and end groups, failing to form an interfacial crystalline layer, resulting in low stress transfer efficiency and insufficient toughening effect. Simultaneously, the lack of hydrophilic channels in the interfacial region hinders water molecule penetration, leading to a significantly slower degradation rate than in the example.

[0046] Compared to Example 1, Comparative Example 2 did not include the catalytic degradation agent zinc stearate. Its mechanical properties were comparable to Example 1, but its disintegration rate was significantly lower. This indicates that while the hydrophilic channels constructed by cyclodextrin can accelerate water molecule penetration and initiate hydrolysis, in the absence of a Lewis acid catalytic degradation agent, the acidic oligomers generated by hydrolysis have a weaker effect on further catalyzing ester bond breakage, demonstrating the existence of a synergistic degradation-promoting effect between the catalytic degradation agent and the hydrophilic channels of cyclodextrin.

[0047] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A self-catalytically degradable PLA composite material, characterized in that, The raw materials include the following parts by weight: 100 parts of polylactic acid, 10-20 parts of modified ethylene-acrylate-glycidyl methacrylate copolymer, and 1-3 parts of catalytic degradation agent; wherein the methacrylate segment of the modified ethylene-acrylate-glycidyl methacrylate copolymer is grafted with cyclodextrin.

2. The PLA composite material according to claim 1, characterized in that, The modified ethylene-acrylate-glycidyl methacrylate copolymer contains 5-10 wt% glycidyl methacrylate.

3. The PLA composite material according to claim 1, characterized in that, The modified ethylene-acrylate-glycidyl methacrylate copolymer is obtained by melt grafting of ethylene-acrylate-glycidyl methacrylate copolymer and cyclodextrin, with a mass ratio of 100:3 to 10.

4. The PLA composite material according to claim 3, characterized in that, The temperature for the fusion grafting is 160–190°C.

5. The PLA composite material according to claim 3, characterized in that, The raw materials for melt grafting also include a methacryloyloxysilane coupling agent, and the mass ratio of the ethylene-acrylate-glycidyl methacrylate copolymer to the methacryloyloxysilane coupling agent is 100:0.5-2.

6. The PLA composite material according to any one of claims 1 to 5, characterized in that, The cyclodextrin is β-cyclodextrin.

7. The PLA composite material according to claim 1, characterized in that, The polylactic acid is poly-L-lactic acid, poly-D-lactic acid, or a blend of the two, and the melt index of the polylactic acid is 5-30 g / 10 min (210℃, 2.16 kg).

8. The PLA composite material according to claim 1, characterized in that, In the ethylene-acrylate-glycidyl methacrylate copolymer, the acrylate is selected from one or more of methyl acrylate, ethyl acrylate, and butyl acrylate.

9. The PLA composite material according to claim 1, characterized in that, The catalytic degradation agent is selected from one or more of iron stearate, zinc stearate, magnesium stearate, zinc oxide, and magnesium oxide.

10. The method for preparing PLA composite material according to any one of claims 1 to 9, characterized in that, The product is obtained by melt blending dried polylactic acid, modified ethylene-acrylate-glycidyl methacrylate copolymer, and catalytic degradation agent, followed by extrusion granulation or direct molding.

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