A biodegradable polylactic acid blended film and a preparation method thereof

Abstract

The application discloses a kind of biodegradable polylactic acid blend film and preparation method thereof, belong to the technical field of degradable film.The film includes the following weight parts raw materials: polylactic acid 45~60 parts, polybutylene adipate terephthalate 30~45 parts, polybutylene succinate 8~15 parts, hyperbranched polyester amide 5~10 parts, plasticizer 3~7 parts, reinforcing filler 4~8 parts, composite fresh-keeping master batch 5~10 parts, processing aid 0.5~2 parts;The reinforcing filler is chitosan intercalation modified montmorillonite.The application is blended by polylactic acid and two kinds of degradable polyester, combined with the synergistic effect of hyperbranched polyester amide, chitosan intercalation modified montmorillonite and composite fresh-keeping master batch, the film not only has excellent mechanical properties and barrier properties, but also has broad-spectrum antibacterial and efficient ethylene adsorption active preservation function, while maintaining complete biodegradable characteristics, has broad application prospect in the field of fresh fruit and vegetable packaging.

Description

Technical Field

[0001] This invention relates to the field of biodegradable film technology, and in particular to a biodegradable polylactic acid blend film and its preparation method. Background Technology

[0002] With the rapid development of the fresh food e-commerce and cold chain logistics industries, the market demand for packaging materials for fresh fruits and vegetables continues to grow. Traditional fresh food packaging mostly uses petroleum-based plastic films such as polyethylene and polypropylene, which are non-biodegradable and lack active preservation functions. Polylactic acid (PLA)-based fully biodegradable films are the core direction for replacing petroleum-based plastics. Their advantages, such as renewable raw materials, excellent biocompatibility, compostability, and good processability, have led to their widespread application in the field of preservation films.

[0003] However, the application of polylactic acid (PLA) materials in food preservation is still limited by their inherent performance defects, among which their high brittleness, insufficient barrier properties, weak antibacterial properties, and lack of preservation function are particularly prominent. Regarding brittleness, PLA molecular chains are rigid and have high crystallinity, with an elongation at break of less than 10% at room temperature. This is especially true in cold chain environments around 4°C, where the mobility of molecular chain segments further decreases. In terms of barrier properties, PLA is a random linear aliphatic polyester with a large free volume of molecular chains, resulting in poor barrier properties against gases such as oxygen, water vapor, and carbon dioxide. It cannot effectively prevent the infiltration of external oxygen leading to oxidative browning in fruits and vegetables, nor can it inhibit the diffusion of ethylene produced by respiration in fruits and vegetables. Furthermore, it easily causes moisture loss and shrinkage in fruits and vegetables, significantly shortening their length. Regarding shelf life, polylactic acid (PLA) has only a weak natural antibacterial effect and cannot effectively inhibit the adhesion and reproduction of common food pathogens such as Escherichia coli and Staphylococcus aureus, leading to easy microbial contamination of food during storage and transportation. In terms of preservation, fresh fruits and vegetables continuously release ethylene through respiration during cold chain storage. Ethylene, as a ripening hormone, is the core factor that accelerates the ripening, aging, and spoilage of fruits and vegetables. Existing PLA-based preservation films are mostly passive barrier packaging, which can only achieve basic protection through physical wrapping. Summary of the Invention

[0004] The purpose of this invention is to provide a biodegradable polylactic acid blend film to solve the problems of polylactic acid films in the prior art, such as high brittleness, insufficient barrier properties, weak antibacterial properties, and lack of preservation function.

[0005] The present invention also aims to provide a preparation method for preparing a biodegradable polylactic acid blend film that simultaneously possesses toughness, barrier properties, antibacterial properties, and preservation functions.

[0006] In a first aspect, the present invention provides a biodegradable polylactic acid blend film, comprising the following raw materials in parts by weight: Polylactic acid 45-60 parts, polybutylene terephthalate-adipate 30-45 parts, polybutylene succinate 8-15 parts, hyperbranched polyester amide 5-10 parts, plasticizer 3-7 parts, reinforcing filler 4-8 parts, composite preservative masterbatch 5-10 parts, processing aid 0.5-2 parts; The reinforcing filler is chitosan-intercalated modified montmorillonite.

[0007] Preferably, the plasticizer includes acetylated tributyl citrate.

[0008] Preferably, the processing aids include hindered phenolic antioxidants and zinc stearate in a mass ratio of 1:(0.5-1).

[0009] More preferably, hindered phenolic antioxidants include antioxidant 1010 and antioxidant 1076.

[0010] Preferably, hyperbranched polyesteramide is prepared by the following method: Under an inert atmosphere, 1,2,4-triphenyltrihydric anhydride, ethanolamine, and p-toluenesulfonic acid catalyst are added to a reaction vessel and stirred for 4–5 hours. The mixture is then washed and dried to obtain the final product.

[0011] Preferably, the reaction temperature is 200–240°C.

[0012] Preferably, the molar ratio of 1,2,4-triphenyltriglycerid acid anhydride to ethanolamine is 1:(0.8-1.2).

[0013] Preferably, chitosan-intercalated modified montmorillonite is prepared by the following method: Chitosan was dissolved in acetic acid solution, the pH was adjusted to 4.8-5.5, montmorillonite was added, and the mixture was reacted at 50-70℃ for 4-10 hours. After washing, chitosan-intercalated modified montmorillonite was obtained.

[0014] Preferably, the mass ratio of chitosan to montmorillonite is 1:(2-5).

[0015] Preferably, the raw materials of the composite preservation masterbatch include polylactic acid, potassium permanganate, modified nano-attapulgite, and ε-polylysine hydrochloride in a mass ratio of 1:(0.05-0.2):(0.2-0.4):(0.01-0.1).

[0016] Preferably, the composite preservation masterbatch is prepared by the following method: A1. Add nano-attapulgite to deionized water, stir and sonicate to obtain a suspension; add aminosilane coupling agent to the suspension, adjust the pH value to 8-9, stir and react at 50-60℃ for 3-5 hours to obtain amino-modified nano-attapulgite. A2. Dissolve potassium permanganate in deionized water to prepare potassium permanganate aqueous solution; soak amino-modified nano-attapulgite in potassium permanganate aqueous solution for 4-6 hours, filter and dry to obtain potassium permanganate-supported amino-modified nano-attapulgite. A3. After uniformly mixing polylactic acid, potassium permanganate-supported amino-modified nano-attapulgite, and ε-polylysine hydrochloride, add the mixture to a twin-screw extruder for melt blending and extrusion at an extrusion temperature of 160-180℃. After cooling in a water bath, pelletizing, and drying, the composite preservation masterbatch is obtained.

[0017] Preferably, in step A1, the aminosilane coupling agent includes one or more of KH550, KH560 or KH570.

[0018] Secondly, the present invention also discloses a method for preparing a biodegradable polylactic acid blend film, comprising the following steps: S1. Mix polylactic acid, polybutylene terephthalate, polybutylene succinate, hyperbranched polyesteramide, plasticizer, reinforcing filler and 1 part of processing aid evenly to obtain a mixture; S2. The mixture is melt-blended and extruded, while composite preservation masterbatch is added by side feeding, and then pelletized to obtain film masterbatch; S3. After drying the film masterbatch, the biodegradable polylactic acid blend film is obtained by casting, biaxial stretching, heat setting, cooling and winding.

[0019] Preferably, in step S2, the melt blending extrusion temperature is 165–190°C and the screw speed is 200–300 rpm.

[0020] Preferably, in step S3, the longitudinal stretching temperature of the biaxial stretching is 85-95°C, and the stretching ratio is 2.5-3.5 times; the transverse stretching temperature is 90-100°C, and the stretching ratio is 3-3.5 times. Preferably, the heat setting temperature is 110–120°C and the setting time is 8–12 seconds.

[0021] The beneficial effects of this invention are: This invention constructs a ternary blend system of polylactic acid (PLA), polybutylene terephthalate (PET), and polybutylene succinate (PSS), and introduces hyperbranched polyesteramide as a compatibility toughening agent. This effectively improves the inherent brittleness of PLA and significantly enhances the elongation at break and impact resistance of the film. The hyperbranched polyesteramide molecule contains a large number of end functional groups, which can form hydrogen bonds with PLA and aliphatic polyesters, promoting the uniform refinement of the dispersed phase and inhibiting phase domain coarsening, thereby achieving a balance between rigidity and toughness. The introduction of chitosan-intercalated modified montmorillonite fully utilizes the physical barrier effect of the nanosheets. Chitosan molecules expand the interlayer spacing of montmorillonite through intercalation, increasing the tortuosity of the gas molecule permeation path. At the same time, the antibacterial activity and polycationic properties of chitosan itself endow the film with antibacterial function. Furthermore, the exfoliation and dispersibility of montmorillonite are significantly improved after intercalation, avoiding the stress concentration defects caused by the easy agglomeration of traditional inorganic fillers. In the composite preservation masterbatch, potassium permanganate is loaded into the porous structure of amino-modified nano-attapulgite, which can achieve continuous adsorption and oxidative decomposition of ethylene gas released by the respiration of fruits and vegetables, thus delaying the ripening and senescence process. ε-polylysine hydrochloride, as a natural antimicrobial peptide, forms a synergistic antimicrobial network with chitosan, showing broad-spectrum inhibitory effects on both Gram-positive and Gram-negative bacteria. Detailed Implementation

[0022] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below.

[0023] A biodegradable polylactic acid blend film, comprising the following raw materials in parts by weight: Polylactic acid 45-60 parts, polybutylene terephthalate-adipate 30-45 parts, polybutylene succinate 8-15 parts, hyperbranched polyester amide 5-10 parts, plasticizer 3-7 parts, reinforcing filler 4-8 parts, composite preservative masterbatch 5-10 parts, processing aid 0.5-2 parts; The reinforcing filler is chitosan-intercalated modified montmorillonite.

[0024] By employing the above technical solutions, this invention synergistically constructs a composite system possessing high toughness, barrier properties, preservation, and antibacterial functions. Specifically, regarding toughness improvement, this invention, on the one hand, uses two flexible biodegradable polyesters, polybutylene terephthalate (PET) and polybutylene succinate (PSS), blended with brittle polylactic acid (PLA) to form an island structure or continuous network structure, effectively absorbing and dispersing impact energy. On the other hand, it introduces hyperbranched polyesteramide, whose unique dendritic molecular structure contains a large number of terminal carboxyl active groups, which can react with the terminal groups of each matrix resin, significantly enhancing the compatibility and bonding force of each phase interface, avoiding performance degradation caused by phase separation, thereby improving film toughness while maintaining high tensile strength. Simultaneously, chitosan intercalation-modified montmorillonite hydroxyl or amino groups can form hydrogen bonds with the carboxyl groups of the hyperbranched polyesteramide, further strengthening the interfacial bonding force between the filler and the matrix, avoiding stress defects caused by filler agglomeration, and maximizing the toughness enhancement effect.

[0025] In terms of improving barrier properties, chitosan-intercalated modified montmorillonite is used as a reinforcing filler. The chitosan molecular chains are inserted into the interlayer of montmorillonite, which not only expands the interlayer spacing of montmorillonite, making it easier to disperse in the polymer matrix, but also the rigid molecular chains of chitosan and the layered structure of montmorillonite together construct a tortuous gas molecule diffusion path, greatly extending the permeation path of oxygen and water vapor. This significantly improves the film's barrier capacity against oxygen and water vapor, effectively preventing oxidative browning and moisture loss in fruits and vegetables. In addition, the antibacterial activity and polycationic properties of chitosan itself can synergistically impart antibacterial function to the film with the composite preservation masterbatch.

[0026] Regarding antibacterial and active preservation functions, this invention designs a composite preservation masterbatch, such as amino-modified nano-attapulgite loaded with potassium permanganate. The nano-attapulgite, as a porous carrier, after amino modification with a silane coupling agent, exhibits excellent adsorption and fixation of potassium permanganate, achieving stable loading of the strong oxidant potassium permanganate. Furthermore, ε-polylysine hydrochloride in the composite preservation masterbatch, as a broad-spectrum antibacterial agent, works synergistically with potassium permanganate. During film application, on the one hand, ε-polylysine hydrochloride effectively inhibits the adhesion and reproduction of common pathogenic bacteria such as Escherichia coli and Staphylococcus aureus; on the other hand, potassium permanganate can continuously and stably oxidize and absorb ethylene gas released by the respiration of fruits and vegetables, thus delaying the ripening and senescence process of fruits and vegetables from the source.

[0027] In some embodiments, the plasticizer includes acetylated tributyl citrate, polycaprolactone, and tributyl citrate.

[0028] In some embodiments, the processing aids include a hindered phenolic antioxidant and zinc stearate in a mass ratio of 1:(0.5 to 1).

[0029] Furthermore, hindered phenolic antioxidants include antioxidant 1010 and antioxidant 1076.

[0030] By adopting the above technical solutions, adding plasticizers can further improve the compatibility between matrices and enhance the ability of molecular chain segments to move, thereby improving the flexibility of the film; while processing aids can ensure the molecular weight and performance stability of the matrix resin.

[0031] In some embodiments, hyperbranched polyesteramide is prepared by the following method: Under an inert atmosphere, 1,2,4-triphenyltriglycerid acid, ethanolamine, and the catalyst p-toluenesulfonic acid are added to a reaction vessel, stirred for 4–5 hours, and then washed and dried to obtain the final product.

[0032] Furthermore, the reaction temperature is 200–240℃; Furthermore, the molar ratio of 1,2,4-triphenyltriglycerid acid anhydride to ethanolamine is 1:(0.8–1.2).

[0033] By adopting the above technical solution, the hyperbranched polyester amide prepared by this method has a large number of active carboxyl groups at the molecular ends. On the one hand, it can form hydrogen bonds with the terminal carboxyl and terminal hydroxyl groups of the polyester matrix, improve the interfacial bonding force between polylactic acid and polybutylene terephthalate and polybutylene succinate, and avoid phase separation. On the other hand, it can combine with the polar groups on the surface of chitosan-intercalated modified montmorillonite to achieve uniform dispersion of inorganic fillers in the matrix and avoid filler agglomeration to form stress defects. At the same time, its unique hyperbranched structure can also play an internal plasticizing role, further improving the elongation at break of the film, and achieving multiple effects of dual-interfacial compatibility, strengthening and toughening.

[0034] In some embodiments, chitosan-intercalated modified montmorillonite is prepared by the following method: Chitosan was dissolved in acetic acid solution, the pH was adjusted to 4.8-5.5, montmorillonite was added, and the mixture was reacted at 50-70℃ for 4-10 hours. After washing, chitosan-intercalated modified montmorillonite was obtained.

[0035] Furthermore, the mass ratio of chitosan to montmorillonite is 1:(2-5).

[0036] By adopting the above technical solutions, chitosan molecular chains can be inserted between the layers of montmorillonite through cation exchange, thus opening up the tightly stacked structure of montmorillonite and achieving single-layer peeling of montmorillonite. The peeled nanosheets form a crisscrossing labyrinth barrier in the matrix, significantly extending the permeation path of gas molecules such as oxygen and water vapor, and significantly improving the barrier performance of the film. At the same time, chitosan is a natural cationic polysaccharide with broad-spectrum antibacterial activity, which can form an antibacterial synergy with ε-polylysine hydrochloride in the composite preservation masterbatch, thereby enhancing the inhibitory effect on pathogenic bacteria.

[0037] In some embodiments, the raw materials of the composite preservation masterbatch include polylactic acid, potassium permanganate, modified nano-attapulgite, and ε-polylysine hydrochloride in a mass ratio of 1:(0.05-0.2):(0.2-0.4):(0.01-0.1).

[0038] Furthermore, the composite preservation masterbatch is prepared by the following method: A1. Add nano-attapulgite to deionized water, stir and sonicate to obtain a suspension; add aminosilane coupling agent to the suspension, adjust the pH value to 8-9, stir and react at 50-60℃ for 3-5 hours to obtain amino-modified nano-attapulgite. A2. Dissolve potassium permanganate in deionized water to prepare potassium permanganate aqueous solution; soak amino-modified nano-attapulgite in potassium permanganate aqueous solution for 4-6 hours, filter and dry to obtain potassium permanganate-supported amino-modified nano-attapulgite. A3. After uniformly mixing polylactic acid, potassium permanganate-supported amino-modified nano-attapulgite, and ε-polylysine hydrochloride, add the mixture to a twin-screw extruder for melt blending and extrusion at an extrusion temperature of 160-180℃. After cooling in a water bath, pelletizing, and drying, the composite preservation masterbatch is obtained.

[0039] Furthermore, in step A1, the aminosilane coupling agent includes one or more of KH550, KH560, or KH570.

[0040] By adopting the above technical solutions, polylactic acid exhibits excellent compatibility with the film matrix, enabling pre-dispersion of functional components and avoiding agglomeration and precipitation problems caused by direct powder addition. Amino-modified nano-attapulgite anchors potassium permanganate through one-dimensional nanopores, achieving efficient and long-lasting ethylene adsorption and oxidative removal, inhibiting post-ripening senescence of fruits and vegetables, and avoiding moisture absorption, inactivation, migration, precipitation, and film discoloration problems caused by direct potassium permanganate addition. Simultaneously, nano-attapulgite can simultaneously achieve ultraviolet shielding and gas barrier, forming a barrier synergy with chitosan-intercalated montmorillonite. ε-polylysine hydrochloride is a food-grade natural antibacterial agent that is resistant to high-temperature processing without inactivation, achieving broad-spectrum and long-lasting antibacterial effects against pathogenic bacteria such as Escherichia coli and Staphylococcus aureus. It forms a triple antibacterial synergy with the amino groups of attapulgite and chitosan, significantly improving the antibacterial effect.

[0041] A method for preparing a biodegradable polylactic acid blend film includes the following steps: S1. Mix polylactic acid, polybutylene terephthalate, polybutylene succinate, hyperbranched polyesteramide, plasticizer, reinforcing filler and 1 part of processing aid evenly to obtain a mixture; S2. The mixture is melt-blended and extruded, while composite preservation masterbatch is added by side feeding, and then pelletized to obtain film masterbatch; S3. After drying the film masterbatch, the biodegradable polylactic acid blend film is obtained by casting, biaxial stretching, heat setting, cooling and winding.

[0042] By adopting the above technical solutions, the base resin, compatibilizer, plasticizer, reinforcing filler, and processing aids are first premixed to obtain a basic mixture. Then, the composite preservation masterbatch is added through side feeding, which can significantly shorten the residence time of functional components in the high-temperature molten state, minimize the thermal deactivation of potassium permanganate and ε-polylysine hydrochloride, and avoid side reactions between the active groups in the functional components and the compatibilizer in the matrix, ensuring the stable performance of compatibility and preservation function. Casting prepares amorphous cast sheets with low crystallinity, laying the foundation for subsequent biaxial stretching. The biaxial stretching process can orient the polyester molecular chains and sheet fillers along the stretching direction, further improving the mechanical properties and barrier properties of the film. The heat setting process can eliminate the internal stress of the film, improve dimensional stability, and prevent the film from shrinking and warping in the low-temperature environment of the cold chain.

[0043] In some embodiments, in step S2, the melt blending extrusion temperature is 165–190°C and the screw speed is 200–300 rpm.

[0044] By adopting the above technical solutions, this temperature range is perfectly matched with the melt processing window of polylactic acid, polybutylene terephthalate, and polybutylene succinate, which not only ensures the complete plasticization and uniform blending of the matrix resin, but also avoids the thermal degradation of polyester and the deactivation of functional components caused by excessively high temperatures.

[0045] In some embodiments, in step S3, the longitudinal stretching temperature of the biaxial stretching is 85-95°C, and the stretching ratio is 2.5-3.5 times; the transverse stretching temperature is 90-100°C, and the stretching ratio is 3-3.5 times. By adopting the above technical solutions, the stretching temperature range is between the glass transition temperature and cold crystallization temperature of polylactic acid. The polyester molecular chains have sufficient mobility to achieve uniform stretching and orientation, avoiding problems such as film breakage and uneven thickness during stretching. The longitudinal stretching ratio of 2.5 to 3.5 times and the transverse stretching ratio of 3 to 3.5 times can enable the molecular chains and sheet fillers to be simultaneously oriented in both directions, forming a regular aggregated structure. This significantly improves the tensile strength, elongation at break, and gas barrier properties of the film, while ensuring the uniformity of the film's performance in both the longitudinal and transverse directions, avoiding defects caused by anisotropy.

[0046] In some embodiments, the heat setting temperature is 110–120°C and the setting time is 8–12 seconds.

[0047] By adopting the above technical solutions, the heat setting temperature of 110-120℃ can cause the stretched and oriented molecular chains to relax and crystallize appropriately, effectively eliminating the internal stress generated during biaxial stretching, significantly improving the thermal dimensional stability of the film, and avoiding problems such as heat shrinkage, warping, and heat sealing cracking during subsequent processing and cold chain use; the setting time of 8-12s can ensure that the crystallization process is fully completed, while avoiding the problem of excessively high crystallinity and increased brittleness of the film caused by excessively long setting time, so that the film has both excellent dimensional stability and flexibility.

[0048] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0049] Preparation Example Preparation Example 1-1: A hyperbranched polyester amide was prepared by the following method: Under a nitrogen atmosphere, 1 mol of 1,2,4-triphenyltriglycerid acid, 1 mol of ethanolamine, and 9.4 mmol of p-toluenesulfonic acid were added to a three-necked flask and stirred at 230 °C for 4 h. The mixture was then washed with methanol and deionized water, and dried at 60 °C to obtain a hyperbranched polyesteramide.

[0050] Preparation Example 2-1: A chitosan-intercalated modified montmorillonite was prepared by the following method: 1 g of chitosan (88% degree of deacetylation) was dissolved in 100 mL of 1% acetic acid solution. The pH was adjusted to 5.0 with 0.1 M sodium hydroxide solution. 3.0 g of sodium montmorillonite was added. The mixture was reacted at 300 rpm and 50 °C for 6 h. The mixture was then washed with deionized water until the pH reached 7. After drying, a chitosan-intercalated modified montmorillonite was obtained.

[0051] Preparation Example 3-1: A composite preservative masterbatch was prepared by the following method: A1. Add 30g of nano-attapulgite to 600mL of deionized water, stir at room temperature for 2h, and then sonicate for 30min to obtain a uniform and stable suspension; add 0.9g of KH550 to the suspension, adjust the pH of the system to 8.5 with ammonia, stir at 55℃ for 4h, collect the precipitate by centrifugation after the reaction, wash three times with anhydrous ethanol, vacuum dry at 80℃, and grind to a particle size of less than 200nm to obtain amino-modified nano-attapulgite. A2. Add 12g of potassium permanganate to 300mL of deionized water and stir at room temperature until completely dissolved to obtain a potassium permanganate aqueous solution. Add all of the amino-modified nano-attapulgite obtained in step A1 to the potassium permanganate aqueous solution and stir and impregnate at 35℃ for 5h. After impregnation, filter using a negative pressure filtration device. Wash the filter cake twice with a small amount of deionized water, vacuum dry at 45℃, and grind it to a particle size of less than 200nm after natural cooling to obtain potassium permanganate-supported amino-modified nano-attapulgite. A3. Add 100g of polylactic acid, all the potassium permanganate-supported amino-modified nano-attapulgite clay obtained in step A2, and 5g of ε-polylysine hydrochloride to a high-speed mixer and mix at 1000rpm for 10min to obtain a uniform mixture. Add the mixture to a twin-screw extruder and melt-blend extrude. The extrusion temperatures in zones one to five are 160℃, 165℃, 175℃, 180℃, and 175℃, respectively, and the screw speed is 220rpm. After the extruded strips are cooled in a water tank and pelletized by a pelletizer, they are vacuum dried at 60℃ for 4h to obtain the composite preservation masterbatch.

[0052] Example Example 1: A biodegradable polylactic acid blend film was prepared by the following method: S1. Mix 50 parts of polylactic acid, 40 parts of polybutylene terephthalate-adipate, 10 parts of polybutylene succinate, 3 parts of hyperbranched polyester amide prepared in Preparation Example 1-1, 5 parts of acetylated tributyl citrate, 6 parts of chitosan intercalated modified montmorillonite prepared in Preparation Example 2-1, and 1 part of processing aid (antioxidant 1010 and zinc stearate in a mass ratio of 1:0.5) evenly to obtain a mixture. S2. The mixture is fed into a twin-screw extruder and melt-blended at a temperature of 190°C. At the same time, 8 parts of the composite preservation masterbatch prepared in Preparation Example 3-1 are added by side feeding and pelletized to obtain film masterbatch. S3. After drying the film masterbatch at 120°C, it is cast into a film at 190°C. After cooling, it is biaxially stretched, with the longitudinal stretching temperature at 90°C and the stretching ratio at 3, and the transverse stretching temperature at 95°C and the stretching ratio at 3. Finally, it is heat-set at 110°C for 10 seconds, cooled and wound to obtain a biodegradable polylactic acid blend film.

[0053] Examples 2 and 3 describe a biodegradable polylactic acid blend film, differing from Example 1 only in the adjustment of the raw material ratios for the blend film, as shown in Table 1. Table 1. Raw material list for Examples 1 to 3

[0054] Comparative Example Comparative Examples 1 to 5: A biodegradable polylactic acid blend film, differing from Example 1 only in the adjustment of the raw material ratio of the blend film, as shown in Table 2: Table 2 Raw material list for Comparative Examples 1 to 4

[0055] Performance testing: The biodegradable polylactic acid blend films prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to the following performance tests: 1. Toughness and strength performance testing shall be conducted in accordance with GB / T 1040.3-2006; 2. Barrier performance test: oxygen transmission rate refers to GB / T 1038.1-2022; water vapor transmission rate refers to GB / T1037-2021. 3. Degradability test: Under industrial composting conditions, the weight loss rate was tested after 6 months at 58℃±2℃. The results of the above performance tests are shown in Table 3. 3. Antibacterial test, refer to QB / T 2591-2003; the antibacterial performance test results are shown in Table 4.

[0056] Table 3 Performance test results

[0057] Table 4 Performance test results

[0058] As shown in Tables 3 and 4, Examples 1 to 3 achieved a synergistic improvement in the mechanical properties, barrier properties, antibacterial preservation properties, and biodegradability of the film by complementing the properties of the ternary polyester matrix, combining the interfacial compatibility of hyperbranched polyester amide, the barrier enhancement effect of chitosan intercalation-modified montmorillonite, and the preservation function of the composite preservation masterbatch. In comparison, Comparative Examples 1 and 2 showed insufficient or no branched polyesteramide, failing to effectively improve the interfacial compatibility between the polyester phase and between the resin and filler. This resulted in severe phase separation, a significant decrease in the tensile strength and elongation at break of the film, and uneven dispersion of the inorganic filler forming gas permeation channels, leading to a significant increase in oxygen and water vapor permeability. This confirms the core role of hyperbranched polyesteramide in maintaining the system's rigidity-toughness balance and interfacial stability. Comparative Example 3, lacking chitosan-intercalated modified montmorillonite, failed to form the labyrinthine barrier effect of nanosheets, resulting in decreased gas barrier performance. Furthermore, the absence of chitosan's auxiliary antibacterial effect and the loss of its synergistic antibacterial effect with the composite preservative masterbatch significantly reduced the film's antibacterial rate. Comparative Example 4, without the addition of the composite preservative masterbatch, relied solely on the weak antibacterial effect of chitosan, failing to achieve broad-spectrum and efficient inhibition of pathogenic bacteria, resulting in a significant decrease in the antibacterial rate. It also lost its ability to adsorb and oxidize ethylene, thus failing to achieve the preservation function.

[0059] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A biodegradable polylactic acid blend film, characterized in that, Including the following parts by weight of raw materials: Polylactic acid 45-60 parts, polybutylene terephthalate-adipate 30-45 parts, polybutylene succinate 8-15 parts, hyperbranched polyester amide 5-10 parts, plasticizer 3-7 parts, reinforcing filler 4-8 parts, composite preservative masterbatch 5-10 parts, processing aid 0.5-2 parts; The reinforcing filler is chitosan-intercalated modified montmorillonite.

2. The biodegradable polylactic acid blend film according to claim 1, characterized in that, The plasticizers include acetylated tributyl citrate, polycaprolactone, and tributyl citrate.

3. The biodegradable polylactic acid blend film according to claim 1, characterized in that, The processing aids include hindered phenolic antioxidants and zinc stearate in a mass ratio of 1:(0.5-1).

4. The biodegradable polylactic acid blend film according to claim 1, characterized in that, The hyperbranched polyesteramide was prepared by the following method: Under an inert atmosphere, 1,2,4-triphenyltrihydric anhydride, ethanolamine, and p-toluenesulfonic acid catalyst are added to a reaction vessel and stirred for 4–5 hours. The mixture is then washed and dried to obtain the final product.

5. The biodegradable polylactic acid blend film according to claim 1, characterized in that, The chitosan-intercalated modified montmorillonite was prepared by the following method: Chitosan was dissolved in acetic acid solution, the pH was adjusted to 4.8-5.5, montmorillonite was added, and the mixture was reacted at 50-70℃ for 4-10 hours. After washing, chitosan-intercalated modified montmorillonite was obtained.

6. The biodegradable polylactic acid blend film according to claim 1, characterized in that, The raw materials of the composite preservation masterbatch include polylactic acid, potassium permanganate, modified nano-attapulgite, and ε-polylysine hydrochloride in a mass ratio of 1:(0.05~0.2):(0.2~0.4):(0.01~0.1).

7. The biodegradable polylactic acid blend film according to claim 6, characterized in that, The composite preservative masterbatch is prepared by the following method: A1. Add nano-attapulgite to deionized water, stir and sonicate to obtain a suspension; add silane coupling agent to the suspension, adjust the pH value to 8-9, stir and react at 50-60℃ for 3-5 hours to obtain amino-modified nano-attapulgite. A2. Dissolve potassium permanganate in deionized water to prepare potassium permanganate aqueous solution; soak amino-modified nano-attapulgite in potassium permanganate aqueous solution for 4-6 hours, filter and dry to obtain potassium permanganate-supported amino-modified nano-attapulgite. A3. After uniformly mixing polylactic acid, potassium permanganate-supported amino-modified nano-attapulgite, and ε-polylysine hydrochloride, add the mixture to a twin-screw extruder for melt blending and extrusion at an extrusion temperature of 160-180℃. After cooling in a water bath, pelletizing, and drying, the composite preservation masterbatch is obtained.

8. A method for preparing a biodegradable polylactic acid blend film according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Mix polylactic acid, polybutylene terephthalate-adipate, polybutylene succinate, hyperbranched polyesteramide, plasticizer, reinforcing filler and 1 part of processing aid evenly to obtain a mixture; S2. The mixture is melt-blended and extruded, while composite preservation masterbatch is added by side feeding, and then pelletized to obtain film masterbatch; S3. After drying the film masterbatch, the biodegradable polylactic acid blend film is obtained by casting, biaxial stretching, heat setting, cooling and winding.

9. The preparation method according to claim 8, characterized in that, In step S2, the melt blending extrusion temperature is 165–190°C and the screw speed is 200–300 rpm.

10. The preparation method according to claim 8, characterized in that, In step S3, the longitudinal stretching temperature of the biaxial stretching is 85-95℃, and the stretching ratio is 2.5-3.5 times; the transverse stretching temperature is 90-100℃, and the stretching ratio is 3-3.5 times.

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