High-strength biodegradable composite film and method for preparing the same

Abstract

The present application relates to the technical field of plastic film, in particular to a high-strength biodegradable composite film and a preparation method thereof.The present application overcomes the shortcomings of poor strength and poor barrier property of the existing film.The present application feeds a mixture of polylactic acid, modified montmorillonite, modified polycaprolactone and stearic acid amide into a double-screw extruder;then step-by-step blends the mixture A and 1,4-butanediol diglycidyl ether;finally, the material is extruded, cooled and granulated to obtain a composite material;the composite material is blown into a film to obtain the composite film;wherein the mixture A comprises polybutylene adipate terephthalate, modified mesoporous nanosilica, zinc laurate and 2-phenylimidazoline;the modified polycaprolactone is prepared from the polycaprolactone, maleic anhydride and dicumyl peroxide.The film prepared by the present application has high strength and good barrier property.

Description

Technical Field

[0001] This invention relates to the field of plastic film technology, specifically to a high-strength biodegradable composite film and its preparation method. Background Technology

[0002] Traditional plastics rely heavily on petroleum-based raw materials. Although they are widely used in packaging, agriculture, and other fields due to their superior mechanical properties and low cost, their non-degradable nature in the natural environment leads to persistent "white pollution" that threatens the ecosystem. With the advancement of environmental protection policies and the improvement of environmental awareness, polyester biodegradable plastics, represented by polylactic acid (PLA), polybutylene adipate / terephthalate (PBAT), and polybutylene succinate (PBS), have become the core direction for alternatives. They can be decomposed by microorganisms or hydrolyzed into harmless substances, effectively alleviating environmental pressure.

[0003] However, the application and promotion of polyester biodegradable plastics are still limited by key performance bottlenecks. In terms of mechanical properties, PLA itself is brittle and has poor compatibility with components such as PBAT and PBS, resulting in low impact strength and insufficient elongation at break of the finished products. It is easily damaged in transportation packaging and heavy-duty packaging scenarios, making it difficult to meet industrial-grade strength requirements. In terms of barrier properties, these materials have weak ability to block oxygen and moisture. When used in food packaging, they can easily cause food oxidation and spoilage. When used to protect precision devices, they can easily cause moisture damage, which greatly limits their application in high-end fields.

[0004] These performance shortcomings not only narrow the scope of polyester biodegradable plastics' substitution for traditional plastics, but also delay the industrialization process of environmentally friendly materials. There is an urgent need to overcome the limitations of existing technologies through precise formula adjustments, interface compatibility optimization, or process improvements, so as to promote their wider practical application.

[0005] To this end, a high-strength biodegradable composite film and its preparation method are proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a high-strength biodegradable composite film and its preparation method. This invention involves feeding a mixture of polylactic acid, modified montmorillonite, modified polycaprolactone, and stearamide into a twin-screw extruder; then, stepwise blending the mixture A with 1,4-butanediol diglycidyl ether; finally, extruding, cooling, and pelletizing the final material to obtain a composite material; and then blowing the composite material into a film to obtain the composite film. The mixture A comprises poly(butylene adipate / terephthalate), modified mesoporous nano-silica, zinc laurate, and 2-phenylimidazoline; the modified polycaprolactone is prepared from the polycaprolactone, maleic anhydride, and dicumyl peroxide. The film prepared by this invention exhibits high strength and good barrier properties.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] Unless otherwise specified, all parts of substances in this invention are parts by mass.

[0009] On one hand, the present invention provides a method for preparing a high-strength biodegradable composite film, specifically including the following steps:

[0010] Polylactic acid (number average molecular weight 90,000–110,000 g / mol), modified montmorillonite, modified polycaprolactone, and stearamide are blended and fed into a twin-screw extruder. The temperatures of zones 1 to 4 are set to 160-165℃, 170-175℃, 175-180℃, and 175-180℃, respectively. Then, mixture A and 1,4-butanediol diglycidyl ether are blended stepwise. Mixture A is fed into the first side feed port of zone 5. The temperatures of zones 5 to 8 are set to... The temperatures are set to 180-185℃, 185-190℃, 185-190℃, and 180-185℃ respectively. 1,4-Butanediol diglycidyl ether is injected into the second side feed port of the ninth zone for blending. The temperatures of zones 9 to 12 are set to 190-195℃, 195-200℃, 195-200℃, and 190-195℃ respectively. The screw speed of the whole machine is 180-220 rpm. After the material is extruded through the die head, it is cooled by a water tank and cut into granules by a pelletizer to obtain the composite material.

[0011] After drying, the composite material is blown into a film. The extruder is set to 170-175℃ in zone 1, 175-185℃ in zone 2, 185-195℃ in zone 3, and 180-190℃ in zone 4, with a die temperature of 185-195℃ and a screw speed of 50 rpm. After the material is plasticized and melted in the extruder, it is extruded, blown in at a blow-in-expansion ratio of 3, cooled and shaped, and finally wound up by a herringbone clamping device, traction rollers, and a winding device to obtain a high-performance biodegradable composite film with a thickness of 0.03 mm.

[0012] The mixture A comprises polybutylene adipate / terephthalate (number average molecular weight 40,000-60,000 g / mol), modified mesoporous nano-silica, zinc laurate, and 2-phenylimidazoline; modified polycaprolactone is prepared from polycaprolactone (number average molecular weight 45,000-55,000 g / mol), maleic anhydride, and dicumyl peroxide; modified montmorillonite is prepared from sodium montmorillonite and hexadecyltrimethylammonium bromide; and modified mesoporous nano-silica is prepared from mesoporous nano-silica and a silane coupling agent.

[0013] Preferably, the modified polycaprolactone is prepared by mixing polycaprolactone, maleic anhydride, and dicumyl peroxide, and then extruding and granulating the mixture in a twin-screw extruder to obtain modified polycaprolactone. The temperatures of each zone are 165-170℃, 175-180℃, 180-185℃, 180-185℃, and 175-180℃, respectively, the die head temperature is 170-175℃, and the screw speed is 120-180 rpm. The mass ratio of polycaprolactone, maleic anhydride, and dicumyl peroxide is 90:8-12:1.5-2.5.

[0014] Preferably, the preparation method of modified montmorillonite is as follows: sodium-based montmorillonite (cation exchange capacity 85-100 mmol / 100 g) is ultrasonically dispersed in 150 parts of deionized water to form a dispersion. A hexadecyltrimethylammonium bromide solution is added to the dispersion and stirred at a constant temperature of 75-85℃ for 3-5 h. After the reaction is completed, the mixture is filtered, washed, and dried to obtain modified montmorillonite. A hexadecyltrimethylammonium bromide solution is obtained by dissolving hexadecyltrimethylammonium bromide in 50 parts of deionized water. The mass ratio of sodium-based montmorillonite to hexadecyltrimethylammonium bromide is 10:3.5-4.5.

[0015] Preferably, the method for preparing modified mesoporous nano-silica is as follows: mesoporous silica (average particle size of 100-200 nm) is dried in a vacuum oven, the dried powder is dispersed in anhydrous toluene to obtain a dispersion, a silane coupling agent is added to the dispersion and refluxed at 105-115℃ for 20-28 h, and after the reaction is completed, the mixture is centrifuged, washed and dried to obtain modified mesoporous nano-silica; the mass ratio of mesoporous silica to silane coupling agent is 10:1-1.6.

[0016] Preferably, the stepwise blending method is as follows: the mixture A is fed into the feed port from the first side of the fifth zone; 1,4-butanediol diglycidyl ether is injected into the feed port from the second side of the ninth zone for blending.

[0017] On the other hand, the present invention provides a high-strength biodegradable composite film, specifically comprising the following components: the raw materials for preparing the high-strength biodegradable composite film include: polylactic acid, modified montmorillonite, modified polycaprolactone, stearamide, poly(butylene adipate / terephthalate), modified mesoporous nano-silica, zinc laurate, 2-phenylimidazoline, and 1,4-butanediol diglycidyl ether.

[0018] Preferably, the silane coupling agent is (3-aminopropyl)triethoxysilane.

[0019] Preferably, the mass ratio of polylactic acid, modified montmorillonite, modified polycaprolactone, stearamide, poly(butylene adipate / terephthalate), modified mesoporous nano silica, zinc laurate, 2-phenylimidazoline, and 1,4-butanediol diglycidyl ether is 60:4-6:5-9:1-2:40:3-5:1-2:0.8-1.2:1.4-2.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. In the initial stage of extrusion, the addition of stearamide plays a dual role. First, as a processing aid, it effectively reduces melt viscosity, thereby promoting the nanoscale exfoliation and ordered arrangement along the shear direction of lamellar montmorillonite in the polylactic acid matrix. Second, as a nucleation site, it initiates the formation of high-density microcrystalline regions in polylactic acid. This physical reinforcing framework, composed of oriented inorganic layers and fine polymer crystals, lays the foundation for the high rigidity, high hardness, and thermal stability of the composite material, thus improving its overall strength.

[0022] 2. In the middle stage of the extrusion process, the maleic anhydride active groups grafted onto the modified polycaprolactone backbone undergo grafting reactions with other polymer chains to form a pre-defined copolymer. Simultaneously, zinc laurate catalyzes transesterification reactions between different polyester macromolecules, generating complex block copolymers in situ at the interfaces. These two compatibilizing mechanisms work synergistically to construct a chemically bonded interfacial layer with gradient characteristics between the phases, effectively suppressing interfacial failure and ensuring that loads can be smoothly transferred from rigid regions to flexible regions, providing a fundamental guarantee for achieving the comprehensive mechanical properties of the material.

[0023] 3. This invention constructs a physically synergistic barrier structure by introducing nanofillers of different morphologies in stages during the process. In the pre-extrusion stage, layered organomontmorillonite is arranged into an ordered barrier substrate under shear force; spherical mesoporous silica added in the middle stage fills the gaps between the montmorillonite layers, further extending the permeation path of gas molecules.

[0024] 4. By injecting 1,4-butanediol diglycidyl ether into the second side feed port after extrusion, and with the synergistic catalysis of the pre-extrusion additives, a stable three-dimensional covalent network is constructed throughout the entire structure. This order of addition ensures that the crosslinking reaction is initiated only after the physical dispersion, filler assembly, and interface compatibilization are fully completed in the early stage, avoiding processing difficulties and uneven dispersion caused by a sharp increase in melt viscosity due to premature crosslinking. This network integrates all polymer matrices and nanofillers into an inseparable whole through chemical bonds. At the same time, this dense covalent network structure forms the final chemical barrier by binding the movement of polymer chain segments and reducing the free volume of the system, further reducing the permeability of the material.

[0025] 5. Zinc ions in zinc laurate can form a dynamic ionic crosslinking network with carboxyl groups on the polymer chain. When the material is subjected to impact or tension, this network can dissipate a large amount of energy through the reversible breaking and recombination of ionic bonds, thereby endowing the material with excellent toughness and elongation at break. On the basis of the high strength and high barrier properties provided by the aforementioned rigid covalent network, the ionic network solves the problem of brittleness of the material, so that the composite material ultimately has excellent comprehensive performance. Attached Figure Description

[0026] Figure 1 The bar chart shows the biodegradation rate test results of Examples 1-5 of the present invention at 60d, 90d, and 120d. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Please see Figure 1 This invention provides a high-strength biodegradable composite film and its preparation method, the technical solution of which is as follows:

[0029] Example 1

[0030] First, modified polycaprolactone was prepared by mixing 90 parts of polycaprolactone, 8 parts of maleic anhydride and 1.5 parts of dicumyl peroxide in a high-speed mixer at 1000 rpm for 5 min. Then, the uniformly mixed material was fed into a twin-screw extruder at a screw speed of 120 rpm for reactive extrusion and granulation to obtain modified polycaprolactone.

[0031] Ten parts of sodium-based montmorillonite were placed in 150 parts of deionized water and dispersed by ultrasonication to obtain a montmorillonite dispersion. Simultaneously, 3.5 parts of hexadecyltrimethylammonium bromide were dissolved in 50 parts of deionized water at 75°C and then added to the montmorillonite dispersion. The system temperature was maintained at 75°C and the mixture was stirred at 500 rpm for 5 hours. After the reaction was completed, the mixture was filtered using a Buchner funnel and the filter cake was washed with deionized water at 90°C until no silver bromide precipitate was formed in the filtrate when tested with 0.1 mol / L silver nitrate solution. Finally, the filter cake was dried in a vacuum oven at 80°C for 40 hours to obtain modified montmorillonite.

[0032] Ten parts of mesoporous silica were dried in a vacuum oven at 120°C for 12 hours. Then, the dried powder was added to a reaction vessel containing anhydrous toluene and ultrasonically dispersed under nitrogen protection. Next, one part of (3-aminopropyl)triethoxysilane was added to the reaction vessel, the system was heated to 105°C and refluxed for 28 hours. After the reaction was completed, the product was collected by centrifugation and washed three times each with anhydrous toluene and anhydrous ethanol. Finally, the product was dried in a vacuum oven at 80°C for 20 hours to obtain modified mesoporous nano silica.

[0033] A twin-screw extruder with a length-to-diameter ratio of 48:1 and 12 temperature zones was used to dry all powdered raw materials in a vacuum oven at 110°C for 12 hours. A mixture of 60 parts polylactic acid, 4 parts modified montmorillonite, 5 parts modified polycaprolactone, and 1 part stearamide was fed into the main feed port. A mixture of 40 parts poly(butylene adipate / terephthalate), 3 parts modified mesoporous silica, 1 part zinc laurate, and 0.8 parts 2-phenylimidazoline was fed into the first side feed port at the fifth barrel. 1.4 parts 1,4-butanediol diglycidyl ether was injected into the second side feed port at the ninth barrel. A vacuum exhaust port was set at the eleventh barrel, maintaining a vacuum of -0.08 MPa. The screw speed was set to 180 r / min. After extrusion through the die head, the material was cooled in a water bath and granulated by a pelletizer to obtain the final composite material.

[0034] The composite material particles were dried in a vacuum oven to reduce their moisture content to below 0.05%. The dried particles were then fed into a single-screw extruder at 50 rpm. After plasticizing and melting in the extruder, the material was extruded, blown up (blow-up ratio 3), cooled and shaped, and finally wound up using a herringbone clamping device, traction rollers, and a winding device to obtain a high-performance biodegradable composite film with a thickness of 0.03 mm.

[0035] The difference between Example 2 and Example 1 is that, in the preparation of modified polycaprolactone, the amount of maleic anhydride added is 10 parts, the amount of dicumyl peroxide added is 2 parts, and the screw speed is 150 rpm; in the preparation of modified montmorillonite, after adding hexadecyltrimethylammonium bromide solution, it is stirred at 80°C for 4 hours, and the mass ratio of sodium montmorillonite to hexadecyltrimethylammonium bromide is 10:4; in the preparation of modified mesoporous nano silica, after adding silane coupling agent, it is refluxed at 110°C for 24 hours, and the mass ratio of mesoporous silica to silane coupling agent is 10:1.3.

[0036] The difference between Example 3 and Example 1 is that, in the preparation of modified polycaprolactone, the amount of maleic anhydride added is 12 parts, the amount of dicumyl peroxide added is 2.5 parts, and the screw speed is 180 rpm; in the preparation of modified montmorillonite, after adding hexadecyltrimethylammonium bromide solution, it is stirred at 85°C for 3 hours, and the mass ratio of sodium montmorillonite to hexadecyltrimethylammonium bromide is 10:4.5; in the preparation of modified mesoporous nano silica, after adding silane coupling agent, it is refluxed at 110°C for 24 hours, and the mass ratio of mesoporous silica to silane coupling agent is 10:1.3.

[0037] The difference between Example 4 and Example 2 is that, in the preparation process of the composite material, the mass ratio of polylactic acid, modified montmorillonite, modified polycaprolactone, stearamide, poly(adipate adipate / butyl terephthalate), modified mesoporous nano silica, zinc laurate, 2-phenylimidazoline, and 1,4-butanediol diglycidyl ether is 60:5:7:1.5:40:4:1.5:1:1.7, and the screw speed of the whole machine is 200 rpm.

[0038] The difference between Example 5 and Example 2 is that, in the preparation process of the composite material, the mass ratio of polylactic acid, modified montmorillonite, modified polycaprolactone, stearamide, poly(adipate adipate / butyl terephthalate), modified mesoporous nano silica, zinc laurate, 2-phenylimidazoline, and 1,4-butanediol diglycidyl ether is 60:6:9:2:40:5:2:1.2:2, and the screw speed of the whole machine is 220 rpm.

[0039] The only difference between Comparative Example 1 and Example 1 is that modified polycaprolactone is not added.

[0040] The only difference between Comparative Example 2 and Example 1 is that, in preparing the composite material, 5 parts of polycaprolactone, 0.5 parts of maleic anhydride and 0.1 parts of dicumyl peroxide were mixed with polylactic acid, modified montmorillonite and stearamide and then fed into a twin-screw extruder, without preparing modified polycaprolactone.

[0041] The only difference between Comparative Example 3 and Example 1 is that no modified montmorillonite is added.

[0042] The only difference between Comparative Example 4 and Example 1 is that, in preparing the composite material, 4 parts of sodium-based montmorillonite and 1 part of hexadecyltrimethylammonium bromide were mixed with polylactic acid, modified polycaprolactone and stearamide and then fed into a twin-screw extruder, without preparing modified montmorillonite.

[0043] The only difference between Comparative Example 5 and Example 1 is that no modified mesoporous nano silica is added.

[0044] The only difference between Comparative Example 6 and Example 1 is that, in the preparation of the composite material, 3 parts of mesoporous nano silica and 0.3 parts of (3-aminopropyl)triethoxysilane were mixed with poly(butylene adipate / terephthalate), zinc laurate and 2-phenylimidazoline and then side-fed, without preparing modified mesoporous nano silica.

[0045] The only difference between Comparative Example 7 and Example 1 is that modified mesoporous nano silica is not added, and the amount of modified montmorillonite is increased to 7 parts.

[0046] The only difference between Comparative Example 8 and Example 1 is that polylactic acid, modified montmorillonite, modified polycaprolactone, stearamide, poly(butylene adipate / terephthalate), modified mesoporous nano silica, zinc laurate, 2-phenylimidazoline, and 1,4-butanediol diglycidyl ether, i.e., all raw materials, are added at the main feed inlet.

[0047] The only difference between Comparative Example 9 and Example 1 is that 1,4-butanediol diglycidyl ether was added to the first side feed port, and poly(butylene adipate / terephthalate), modified mesoporous nano silica, zinc laurate and 2-phenylimidazoline were added to the second side feed port.

[0048] The only difference between Comparative Example 10 and Example 1 is that zinc laurate is not added.

[0049] The only difference between Comparative Example 11 and Example 1 is that stearamide is not added.

[0050] The only difference between Comparative Example 12 and Example 1 is that stearamide and 2-phenylimidazoline are not added.

[0051] The only difference between Comparative Example 13 and Example 1 is that 1,4-butanediol diglycidyl ether is not added.

[0052] Test Example 1

[0053] Test subjects: Thin films prepared in Examples 1-5, Comparative Examples 1-4, and Comparative Examples 8-13 were tested.

[0054] Test method: Following standard ASTM D638, the test was conducted on an Instron 2367 universal testing machine at a tensile speed of 20 mm / min. In the obtained tensile curves, the yield stress was taken as the tensile strength, and the fracture point strain as the elongation at break. The final test results are shown in Table 1.

[0055] Table 1. Results of Mechanical Performance Tests

[0056]

[0057] Comparative Example 1, lacking a compatibilizer, exhibited incompatibility between polylactic acid and poly(adipate adipate / butyl terephthalate) at the interface, resulting in inability to transfer stress and lower strength and toughness. Comparative Example 2, employing a one-step mixing method to modify polycaprolactone raw materials, suffered from insufficient in-situ grafting efficiency, leading to weaker interfacial bonding compared to examples using pre-modified polycaprolactone and limited improvement in mechanical properties. Comparative Example 3, lacking montmorillonite, resulted in a decrease in the tensile strength and modulus of the material. Comparative Example 4, using unmodified montmorillonite, formed aggregates in the matrix, creating stress concentration points and simultaneously deteriorating both the strength and toughness of the material. Comparative Examples 8 and 9, respectively... By adding materials in one go and reversing the order of addition, the sequential reaction process was disrupted, resulting in a chaotic and defective system structure and poor mechanical properties. Comparative Example 10 lacked zinc laurate, which weakened the interfacial ester exchange compatibilization and lacked an ionic crosslinking network, leading to a loss of toughness. Comparative Example 11 lacked stearamide, which affected the physical reinforcement effect of montmorillonite and the crystallinity of polylactic acid, resulting in a reduction in strength and stiffness. Comparative Example 12 lacked a synergistic catalyst, resulting in incomplete covalent network crosslinking, and its strength and toughness could not reach the set values. Comparative Example 13, on the other hand, lacked a covalent network skeleton, resulting in insufficient material strength and modulus.

[0058] In summary, Comparative Examples 3 and 4 demonstrate that introducing modified rigid fillers is a prerequisite for providing basic strength. Building upon this, Comparative Examples 1, 2, and 10 demonstrate that interface issues must be addressed through compatibilization techniques to effectively combine the rigid matrix with the flexible phase. Furthermore, Comparative Examples 11 and 12 reveal the need for synergistic effects of additives to optimize physical morphology and catalytic efficiency, creating conditions for the final network construction. Finally, Comparative Examples 8, 9, and 13, by demonstrating the role of process and chemical reactions, prove that the dual-crosslinked network constructed under sequential reaction processes is the guarantee for integrating all previously optimized physical structures and chemical interfaces into a high-performance whole. The failure of each comparative example represents the loss of a single function and the disruption of the entire synergistic enhancement chain, thus systematically demonstrating the indispensability of each technical feature in the embodiment schemes.

[0059] Test Example 2

[0060] Test subjects: Thin films prepared in Examples 1-5 and Comparative Examples 5-9 and 12-13 were tested.

[0061] Test method: The barrier properties of the thin film were tested according to the test methods of GB / T1038-2000 and GB / T1037-1988. The final test results are shown in Table 2.

[0062] Table 2 Barrier Performance Test Results

[0063]

[0064] Comparative Example 5 lacked mesoporous nano-silica, resulting in large gaps and unstable orientation between montmorillonite layers, reducing the tortuosity of the physical barrier path. Comparative Example 6 used unmodified silica, which agglomerated in the matrix and formed interfacial pores, failing to provide synergistic barrier effects. Comparative Example 7 replaced silica with more montmorillonite, demonstrating that single-form fillers, at high concentrations, could not form optimal barrier paths due to their own stacking. Comparative Examples 8 and 9, due to disordered process timing, failed to form ordered physical barrier structures and solidified numerous interfacial defects, leading to decreased barrier performance. Comparative Example 12, due to reduced synergistic catalytic efficiency and insufficient covalent network crosslinking density, weakened the binding ability of polymer segments, resulting in a relatively large free volume. Comparative Example 13, lacking any covalent crosslinking network, lacked the chemical barrier achieved by reducing free volume.

[0065] In summary, Comparative Examples 5, 6, and 7 collectively demonstrate that the construction of the first and second-level physical barrier requires surface modification of the filler and the synergistic assembly of two different filler morphologies to form an optimized physical barrier structure. Building upon this physical foundation, Comparative Examples 8 and 9 demonstrate from a process perspective that following the correct reaction sequence is essential to protect and solidify the physical structure and eliminate interfacial defects. Finally, Comparative Examples 12 and 13 reveal the role of the third-level chemical barrier: given the physical barrier structure and defect-free interface, a dense chemical cross-linked network must be constructed through synergistic catalytic reactions to suppress gas molecule diffusion by reducing the system's free volume. This indicates that improving the barrier performance of thin films is an indispensable result of physical morphology control, interfacial elimination, and chemical network densification.

[0066] Test Example 3

[0067] Test subjects: Thin films prepared in Examples 1-5 were tested.

[0068] Test method: The degradation rate was tested according to GB / T20197-2006 standard, and the biodegradation rate was tested at 60d, 90d, and 120d. The results are shown in Table 3. The final test results are shown in Table 3 and... Figure 1 As shown.

[0069] Table 3 Degradation Rate Test Results

[0070]

[0071] The high-performance biodegradable composite film prepared by this invention has core components, polylactic acid (PLA) and poly(butylene adipate / terephthalate), both of which are biodegradable by microorganisms. In environments rich in microorganisms and characterized by humidity and heat, such as composting, the material first undergoes hydrolysis, breaking down the long polymer chains into oligomers and monomers such as lactic acid, adipic acid, terephthalic acid, and butanediol. Subsequently, these small molecules can be further absorbed and metabolized by microorganisms as carbon and energy sources, ultimately decomposing into carbon dioxide, water, and biomass. The organic montmorillonite and mesoporous silica introduced into the system are both natural inorganic minerals, harmless to the environment. Simultaneously, organic additives such as stearamide and zinc laurate are themselves biodegradable or biocompatible. Therefore, the entire composite material system can achieve complete biodegradation after use and disposal, returning to the natural cycle and effectively solving the environmental pollution problems caused by traditional plastic packaging.

[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-strength biodegradable composite film, characterized in that: The specific steps include: using a twin-screw extruder with a length-to-diameter ratio of 48:1 and 12 temperature zones, all powdered raw materials are dried in a vacuum oven at 110°C for 12 hours; a mixture of 60 parts polylactic acid, 4 parts modified montmorillonite, 5 parts modified polycaprolactone, and 1 part stearamide is fed into the main feed port; at the first side feed port in the fifth barrel, 40 parts poly(butylene adipate / terephthalate), 3 parts modified mesoporous nano-silica, and 1 part zinc laurate are fed into the machine. A mixture of 0.8 parts of 2-phenylimidazoline was used; 1.4 parts of 1,4-butanediol diglycidyl ether were injected into the second side feed port at the 9th barrel, and a vacuum exhaust port was set at the 11th barrel, maintaining a vacuum of -0.08 MPa; the screw speed of the whole machine was set to 180 r / min, and after the material was extruded through the die head, it was cooled by a water tank and cut into granules by a pelletizer to finally prepare the composite material; the composite material was blown into a film to obtain the composite film; The modified polycaprolactone was prepared from polycaprolactone, maleic anhydride and dicumyl peroxide; The modified montmorillonite is prepared by ultrasonically dispersing sodium montmorillonite in deionized water to form a dispersion, adding hexadecyltrimethylammonium bromide solution to the dispersion and stirring at a constant temperature, and after the reaction is completed, filtering, washing and drying to obtain the modified montmorillonite. The modified mesoporous nano-silica is prepared by: drying the mesoporous silica and dispersing it in anhydrous toluene to obtain a dispersion; adding a silane coupling agent to the dispersion and refluxing the reaction; and centrifuging, washing, and drying the mixture after the reaction to obtain the modified mesoporous nano-silica.

2. The method for preparing a high-strength biodegradable composite film according to claim 1, characterized in that: The modified polycaprolactone is prepared by mixing the polycaprolactone, maleic anhydride and dicumyl peroxide, and then extruding and granulating the mixture in a twin-screw extruder to obtain the modified polycaprolactone.

3. A high-strength biodegradable composite film prepared by the method described in claim 1, characterized in that: Specifically, the raw materials for preparing the high-strength biodegradable composite film include: polylactic acid, modified montmorillonite, modified polycaprolactone, stearamide, poly(butylene adipate / terephthalate), modified mesoporous nano silica, zinc laurate, 2-phenylimidazoline, and 1,4-butanediol diglycidyl ether.

4. The high-strength biodegradable composite film according to claim 3, characterized in that: The silane coupling agent is (3-aminopropyl)triethoxysilane.

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