Reactive compatibilized active polylactic acid packaging material as well as preparation method and application thereof

Abstract

The invention belongs to the field of food packaging materials, and particularly relates to a reactive compatibilization active polylactic acid packaging material as well as a preparation method and application thereof. The reactive compatibilization active antioxidant antibacterial polylactic acid material is prepared from polylactic acid, tannic acid and a polylactic acid and maleic anhydride grafted copolymer through blending and melt extrusion processes, and the polylactic acid and maleic anhydride grafted copolymer is prepared from polylactic acid, maleic anhydride and an initiator through blending and melt extrusion processes. The packaging film can be used for packaging food or flowers, effectively delaying browning, inhibiting microbial growth, maintaining hardness and quality and prolonging shelf life. The raw materials are green and degradable, the process is simple and continuous, the method is suitable for industrial production, and a new way is provided for development of active functional packaging.

Description

Technical Field

[0001] This invention belongs to the field of food packaging materials, specifically relating to an active antioxidant packaging film that is constructed in situ through melt extrusion of a polylactic acid / tannic acid compatible system, its preparation method, and its application. Background Technology

[0002] The environmental pollution caused by the non-degradability of petroleum-based plastic packaging materials is becoming increasingly serious, making the development of green and biodegradable alternatives an urgent need in the food packaging industry. Polylactic acid (PLA), as an important bio-based biodegradable material, has advantages such as renewable sources, good processing performance, and high biocompatibility, and is considered one of the ideal alternatives to traditional plastics. However, pure PLA film itself has limited functionality, lacking antioxidant and antibacterial properties, and its gas barrier properties and mechanical toughness still need improvement. The addition of antioxidant and antibacterial active ingredients to improve the active functions of pure PLA film significantly reduces its barrier properties and mechanical toughness, limiting its high-end application in the preservation packaging of perishable foods such as fresh fruits and vegetables.

[0003] To impart functionality to PLA films, researchers often blend them with natural active substances (such as plant polyphenols and essential oils). Tannic acid (TA), as a natural polyphenol compound, possesses excellent antioxidant and broad-spectrum antibacterial properties, making it an ideal active additive. However, TA is rich in phenolic hydroxyl groups and is a highly polar substance, while PLA is a non-polar polymer, resulting in extremely poor compatibility between the two. If directly and simply blended, TA readily undergoes severe phase separation and aggregation in the PLA matrix, leading to pores and interfacial defects in the composite film. This not only severely degrades the film's mechanical and barrier properties but also causes uneven distribution of active ingredients, uncontrollable functional release, and even prevents film formation due to severe aggregation. Therefore, improving the interfacial compatibility between PLA and TA is a core challenge in achieving the preparation of high-performance PLA / TA active films.

[0004] Existing methods for improving incompatible polymer blends mainly include adding compatibilizers and chemically modifying the matrix or fillers. While chemical modification methods are highly effective, they often involve complex synthetic routes, high costs, or the use of toxic reagents, making it difficult to meet the dual requirements of safety and economy in food packaging materials. Physical blending with compatibilizers, although simple in process, often lacks specific interactions between most compatibilizers and the active ingredient, resulting in limited compatibilization effects and potentially introducing new incompatible interfaces. Developing a simple, efficient, and scalable PLA / TA compatibilization method is crucial for promoting the practical application of functional biodegradable packaging materials. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention proposes an innovative "reactive melt extrusion compatibilization" strategy. This method uses commercially available PLA as raw material. During melt extrusion, an initiator is used to generate free radicals in the PLA molecular chain, which then undergo an in-situ grafting reaction with the polar graft monomer maleic anhydride (MAH) to generate PLA-g-MAH. This grafted product simultaneously possesses non-polar segments of PLA and polar anhydride / carboxyl groups of MAH, serving as a "polymer bridging agent." Subsequently, it is melt-blended again with the PLA matrix and TA. The non-polar portion of PLA-g-MAH is compatible with the PLA matrix, while the polar portion tightly binds to the phenolic hydroxyl groups of TA through hydrogen bonds and other interactions, thereby constructing a stable "anchoring" interface between PLA and TA. This significantly improves the dispersibility and interfacial bonding of TA in the PLA matrix, ultimately yielding a PLA / TA active packaging film with uniform structure, controllable mechanical properties, and long-lasting antioxidant / antibacterial functions. The present invention provides a simple and continuous process for preparing an active antioxidant and antibacterial packaging film with a polylactic acid / tannic acid compatible system via melt extrusion, suitable for industrial production. The active antioxidant and antibacterial packaging film prepared by melt extrusion of the present invention exhibits a uniform distribution of the active phase, excellent antioxidant and antibacterial properties, controllable gas permeability, and good biodegradability. It is suitable for food preservation, especially for climacteric fruits and vegetables such as peaches, effectively delaying browning, inhibiting microbial growth, and extending shelf life.

[0006] This invention provides a reactive compatibilizing active polylactic acid packaging material, which is prepared by blending and melt extrusion of polylactic acid, tannic acid, and a polylactic acid-maleic anhydride graft copolymer. The polylactic acid-maleic anhydride graft copolymer is prepared by blending and melt extrusion of polylactic acid, maleic anhydride, and an initiator.

[0007] The mass ratio of polylactic acid, tannic acid, and the polylactic acid-maleic anhydride graft copolymer is (65~80):(3~9):(20-35), further (70~75):(6~9):(25-30), further (72~73):(7~9):(27-28), and even further (72~73):(8~9):(27-28); the mass ratio of polylactic acid, maleic anhydride, and initiator in the polylactic acid-maleic anhydride graft copolymer is 100:(6~10):(0.3~0.7), further 100:(8~9):(0.4~0.6), and further 100:(8~8.5):(0.5~0.55); the initiator is dicumyl peroxide.

[0008] The reactive compatibilized polylactic acid (PLA) packaging material provided by this invention is in the form of strips, granules, or films. When the reactive compatibilized PLA packaging material provided by this invention is in the form of strips or granules, the melt extrusion process of the PLA, tannic acid, and PLA-maleic anhydride graft copolymer is a melt extrusion pelletizing process, with a temperature of 150℃-170℃ and a screw speed of 80-120 r / min, preferably 90-110 r / min. When the reactive compatibilized polylactic acid packaging material provided by the present invention is in the form of a film, the melt extrusion process of the polylactic acid, tannic acid, and polylactic acid-maleic anhydride graft copolymer includes a melt extrusion pelletizing process and a melt extrusion casting process performed sequentially, or includes a melt extrusion pelletizing process and a hot pressing film forming process performed sequentially. The temperature of the melt extrusion pelletizing process is 150℃-170℃, and the screw speed is 80-120 r / min, preferably 90-110 r / min; the temperature of the melt extrusion casting process is 150℃-175℃, and the screw speed is 30-80 r / min, preferably 30-60 r / min.

[0009] The melt extrusion process of polylactic acid, maleic anhydride and initiator is a melt extrusion pelletizing process, with a temperature of 150℃-165℃ and a screw speed of 30-100r / min, preferably 30-60r / min.

[0010] The thickness of the reactive compatibilized polylactic acid packaging film provided by this invention is controlled between 35-45 μm.

[0011] This invention provides a method for preparing a reactive compatibilized active polylactic acid (PLA) packaging material, comprising the steps of: blending polylactic acid, tannic acid, and a PLA-g-MAH graft copolymer, followed by melt extrusion to obtain strip-shaped or granular active PLA packaging material. The polar anhydride / carboxyl groups on the PLA-g-MAH molecular chain are tightly bonded to the phenolic hydroxyl groups on the tannic acid (TA) molecules through strong interactions such as hydrogen bonds, while the non-polar PLA segments are well-compatible with the PLA matrix, significantly improving the dispersibility and interfacial bonding of tannic acid (TA) in the PLA matrix.

[0012] The melt extrusion temperature is 150℃-170℃. Specifically, the temperatures of each zone of the screw extruder from the feed inlet to the die are 150℃, 155℃, 165℃, 170℃, 165℃, 165℃, 165℃, 160℃, and 155℃ respectively. The screw speed is 80-120 r / min, preferably 90-110 r / min.

[0013] The mass ratio of polylactic acid, tannic acid, and polylactic acid graft copolymer to maleic anhydride is (65~80):(3~9):(20-35), further (70~75):(6~9):(25-30), further (72~73):(7~9):(27-28), and even further (72~73):(8~9):(27-28).

[0014] The preparation of the polylactic acid-maleic anhydride graft copolymer includes: blending polylactic acid, maleic anhydride, and an initiator, followed by melt extrusion to obtain the polylactic acid-maleic anhydride graft copolymer in strip or granular form, preferably in granular form. The melt extrusion temperature is 150℃-165℃. Specifically, the temperatures of each zone of the screw extruder from the feed inlet to the die are 155℃, 160℃, 165℃, 165℃, 165℃, 165℃, 160℃, 155℃, and 150℃ respectively; the screw speed is 30-100 r / min, preferably 30-60 r / min. The mass ratio of polylactic acid, maleic anhydride and initiator is 100:(6~10):(0.3~0.7), more specifically 100:(8~9):(0.4~0.6), more specifically 100:(8~8.5):(0.5~0.55); the initiator is dicumyl peroxide.

[0015] The free radicals generated by the decomposition of dicumyl peroxide (DCP) initiate the breakage of PLA molecular chains and generate macromolecular free radicals. These free radicals undergo a graft copolymerization reaction with maleic anhydride (MAH) to generate polylactic acid-maleic anhydride graft copolymer PLA-g-MAH.

[0016] Furthermore, it also includes melting and extruding granular active polylactic acid packaging materials into films through a melt extrusion casting process or a hot pressing film forming process to obtain thin film-like active polylactic acid packaging materials.

[0017] The temperature of the melt extrusion casting process is 150℃-175℃. Specifically, the temperatures of each zone of the screw extruder from the feed inlet to the die are 150℃, 155℃, 160℃, 165℃, 175℃, 175℃, 175℃, 175℃, 170℃, 170℃, 170℃, and 170℃ respectively. The screw speed is 30-80 r / min, preferably 30-60 r / min.

[0018] The thickness of the reactive compatibilized polylactic acid packaging film prepared by the above preparation method of the present invention is controlled between 35-45 μm.

[0019] The reactive compatibilizing polylactic acid packaging material (film) provided by the present invention exhibits a microstructure in which tannic acid (TA) is uniformly dispersed within a polylactic acid (PLA) matrix, forming a strong interfacial bond through PLA-g-MAH. Under conditions of 23°C and 70% relative humidity, its oxygen permeability (OTR) is 240~550 cm⁻¹. 3 / m 2 • 24h • 0.1MPa, optimal oxygen permeability is 285~434cm 3 / m 2 At 0.1 MPa for 24 hours, the water vapor transmission rate (WVP) is 176~573 g / m². 2 • 24h. This film exhibits a scavenging rate of no less than 95% for 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) free radicals and a significant inhibitory effect on Staphylococcus aureus. When used for packaging fruits and vegetables (such as peaches as shown in the verification example), under storage conditions of 20-25℃, it can effectively remove reactive oxygen free radicals in the packaging microenvironment, inhibit the proliferation of spoilage microorganisms, and regulate the respiratory metabolism of fruits and vegetables, thereby significantly delaying fruit weight loss, decreased firmness, browning, and spoilage. During the storage period, it can extend the commercial shelf life of fruits and vegetables (compared to pure polylactic acid film packaging) by 100%.

[0020] The reactive compatibilizing polylactic acid packaging material provided by the present invention can be used for packaging food or flowers, or for preparing packaging. The packaging includes, but is not limited to, cans, bottles, bags, rolls, boxes, cartons, films, etc. The food includes, but is not limited to, fruits, vegetables, meat and meat products, eggs and egg products, milk and dairy products, aquatic products and their products, etc., and is particularly suitable for climacteric foods or high-value foods, and even more suitable for climacteric fruits and vegetables or high-value fruits and vegetables, such as peaches, apples, mangoes, pears, bananas, tomatoes, lychees, etc.; the flowers are particularly suitable for climacteric flowers.

[0021] This invention provides a packaging material containing the reactive compatibilizing active polylactic acid packaging material provided above, particularly the reactive compatibilizing active polylactic acid packaging film provided above. The food packaging includes, but is not limited to, cans, bottles, bags, rolls, boxes, and cartons. The packaging can be used to package food or flowers. Foods include, but are not limited to, fruits, vegetables, meat and meat products, eggs and egg products, milk and dairy products, aquatic products and their products, etc. It is particularly suitable for packaging climacteric foods or high-value foods, and even more suitable for packaging climacteric fruits and vegetables and flowers, such as peaches, apples, mangoes, pears, bananas, tomatoes, and lychees; the flowers are particularly suitable for climacteric flowers.

[0022] Compared with the prior art, the present invention has the following significant advantages: Innovative Compatibilization Strategy: This invention creatively employs "reactive melt extrusion" to prepare PLA-g-MAH as a reactive compatibilizer. In subsequent blending, this compatibilizer, through its amphiphilic molecular structure (one end affinity for PLA, the other for TA), constructs a robust molecular-level "anchoring" interface between the incompatible PLA and TA, fundamentally solving the problem of TA's easy aggregation and phase separation in PLA, thus achieving a high content (up to 9 wt%) and uniform dispersion of the active ingredient.

[0023] Excellent and balanced performance: Through the aforementioned capacity-enhancing strategy, this invention imparts to the film superior antioxidant properties (DPPH scavenging rate ≥95%) and significant antibacterial properties, while effectively mitigating the drastic decline in mechanical properties (such as tensile strength) caused by the addition of active substances. Furthermore, the oxygen and water vapor permeability of the film is controlled within a suitable "window" for modified atmosphere storage of fruits and vegetables, suppressing excessive respiration while avoiding anaerobic respiration, thus achieving a balance between functionality and preservation suitability.

[0024] Active and Intelligent Preservation: The film of this invention is not a simple physical barrier, but an "active" packaging with active functions. The continuous release of TA actively eliminates free radicals produced by fruits and vegetables and inhibits common spoilage bacteria, delaying spoilage at both physiological and microbiological levels. When used for preserving peaches, its shelf life can be extended from 6 days to more than 12 days compared to PLA film groups, demonstrating a significant preservation effect.

[0025] Green and Industrial Prospects: The entire preparation process is a fully melt-processing process, requiring no solvents and producing no wastewater or exhaust emissions, aligning with green manufacturing principles. The process flow is simple, with grafting, blending, and film formation all utilizing mature plastic extrusion equipment, facilitating large-scale, continuous, and low-cost industrial production, paving the way for the market promotion of bio-based active packaging materials.

[0026] Environmentally friendly and sustainable: The main raw material of the film, PLA, is a bio-based biodegradable polyester, and TA is a natural plant extract. The overall composition is safe and non-toxic. Based on the inherent properties of the materials, this film has the potential to be completely biodegradable after disposal, fundamentally avoiding the "white pollution" problem of traditional petroleum-based plastics, and aligning with the concepts of circular economy and sustainable development. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the process flow for preparing active thin films in this embodiment of the invention, including core steps such as grafting reaction, premixing, blending and granulation, and casting.

[0028] Figure 2 The image shows a comparison of the Fourier transform infrared (FTIR) spectra of polylactic acid (PLA), maleic anhydride (MAH), and the grafted product PLA-g-MAH, proving that the grafting reaction was successful.

[0029] Figure 3 These are scanning electron microscope (SEM) surface morphology comparison images of different thin films, demonstrating the uniformity of TA dispersion.

[0030] Figure 4 These are scanning electron microscope (SEM) cross-sectional morphology comparison images of different thin films, demonstrating the compactness of their microstructures.

[0031] Figure 5 This is a bar chart comparing the DPPH free radical scavenging rates of different films.

[0032] Figure 6 The antibacterial effects of different films on Staphylococcus aureus.

[0033] Figure 7 This is a graph showing the changes in O2 and CO2 concentrations in the headspace gas inside the packaging bags of peaches packaged with different films during storage.

[0034] Figure 8 This is a graph showing the weight loss rate of peaches packaged with different films during storage.

[0035] Figure 9 This is a graph showing the change in hardness of peaches packaged with different films during storage.

[0036] Figure 10 This is a graph showing the browning index changes of peaches packaged with different films during storage.

[0037] Figure 11 This is a graph showing the change in total bacterial count of peaches packaged with different films during storage.

[0038] Figure 12 This is a graph showing the changes in polyphenol oxidase (PPO) activity in peaches packaged with different films during storage.

[0039] Figure 13 This is a graph showing the change in malondialdehyde (MDA) content in peaches packaged with different films during storage. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited thereto. Unless otherwise specified, all amounts in the embodiments are by weight.

[0041] Example 1: Preparation of PLA / TA-3% (unmodified) thin film This embodiment aims to demonstrate the thin film performance of TA directly blended without PLA-g-MAH compatibilization.

[0042] (1) Premixing: Mix 100 parts by weight of polylactic acid (PLA 4032D) and 3 parts by weight of tannic acid (TA) powder in a high-speed mixer at room temperature for 15 minutes to ensure initial uniform mixing.

[0043] (2) Melt blending and granulation: The above mixture was fed into the feed hopper of a twin-screw extruder. The temperatures of the twin-screw extruder from zone one to zone nine were set to 150℃, 155℃, 165℃, 170℃, 165℃, 165℃, 165℃, 160℃, and 155℃, respectively. The screw speed was set to 100 r / min. After melting and mixing, the material was extruded into strips through the die, cooled in a water bath, and then cut into granules by a pelletizer to obtain PLA / TA-3% composite masterbatch. The masterbatch was dried in a 70℃ forced-air drying oven for 6 hours for later use.

[0044] (3) Extrusion film formation: The dried composite masterbatch is fed into a casting extruder. The temperatures of each zone of the screw extruder barrel are set sequentially from the feed inlet to the die as follows: 150℃, 155℃, 160℃, 165℃, 175℃, 175℃, 175℃, 175℃, 170℃, 170℃, 170℃. The screw speed is set to 40 r / min. After the molten material flows out of the slit die, it is cooled and drawn by the casting rollers, and finally wound up to obtain a PLA / TA-3% antioxidant film with a thickness of 40±5 μm.

[0045] Example 2: Preparation of MPLA / TA-3% thin film This embodiment is one of the basic implementations of the present invention, and aims to demonstrate that, after compatibilization with PLA-g-MAH, the prepared film is superior to the unmodified comparative example even at a relatively low TA content.

[0046] (1) Grafting reaction (preparation of compatibilizer): 100 parts by weight of polylactic acid (PLA 4032D), 8 parts by weight of maleic anhydride (MAH), and 0.5 parts by weight of dicumyl peroxide (DCP) were uniformly mixed. The mixture was fed into a twin-screw extruder. The temperatures of each zone of the extruder were set as follows: 155℃, 160℃, 165℃, 165℃, 165℃, 160℃, 155℃, and 150℃. The screw speed was 40 r / min. After extrusion, the reaction product was cooled and pelletized to obtain PLA-g-MAH grafted masterbatch.

[0047] (2) Premixing and granulation: Weigh 27.3 parts by weight of the above PLA-g-MAH grafted masterbatch, 72.7 parts by weight of pure polylactic acid (PLA 4032D), and 3 parts by weight of tannic acid (TA) powder (based on a total weight of 100 parts of PLA-g-MAH and pure PLA, the amount of TA added is 3 parts). Mix thoroughly to obtain the premix.

[0048] The premixed material was fed into a screw extruder for blending and granulation. The temperatures of each zone of the extruder were set as follows: 150℃, 155℃, 165℃, 170℃, 165℃, 165℃, 165℃, 160℃, and 155℃. The screw speed was 100 r / min. After cooling and pelletizing, MPLA / TA-3% active composite masterbatch was obtained and dried at 70℃ for 6 hours.

[0049] (3) Extrusion film formation: The dried active composite masterbatch was fed into a single-screw casting extruder. The temperature of each zone of the barrel was set to be the same as in step (3) of Example 1. The screw speed was 40 r / min. The molten material was cast, cooled, and drawn, and finally wound up to obtain an MPLA / TA-3% active antioxidant film with a thickness of 40±5 μm.

[0050] Example 3: Preparation of MPLA / TA-6% thin film This embodiment is one of the preferred embodiments of the present invention, demonstrating the preparation of a thin film with a high TA content by PLA-g-MAH compatibilization.

[0051] (1) Grafting reaction (preparation of compatibilizer): The PLA-g-MAH grafted masterbatch was prepared in exactly the same way as in step (1) of Example 2.

[0052] (2) Premixing and granulation: Weigh 27.3 parts by weight of the above-mentioned PLA-g-MAH grafted masterbatch, 72.7 parts by weight of pure polylactic acid (PLA 4032D), and 6 parts by weight of tannic acid (TA) powder (based on a total weight of 100 parts of PLA-g-MAH and pure PLA, the amount of TA added is 6 parts). The mixing and granulation process parameters are exactly the same as those in step (2) of Example 2.

[0053] The premixed material was fed into a screw extruder for blending and granulation. The temperatures of each zone of the extruder were set as follows: 150℃, 155℃, 165℃, 170℃, 165℃, 165℃, 165℃, 160℃, and 155℃. The screw speed was 100 r / min. After cooling and pelletizing, MPLA / TA-6% active composite masterbatch was obtained and dried at 70℃ for 6 hours.

[0054] (3) Extrusion film formation: The dried active composite masterbatch was fed into a single-screw casting extruder. The temperature of each zone of the barrel was set to be the same as in step (3) of Example 1. The screw speed was 40 r / min. The molten material was cast, cooled, and drawn, and finally wound up to obtain an MPLA / TA-6% active antioxidant film with a thickness of 40±5 μm.

[0055] Example 4: Preparation of MPLA / TA-9% thin film This embodiment is another preferred embodiment of the present invention, demonstrating the successful preparation of a high TA content (9%) thin film through compatibilization technology.

[0056] (1) Grafting reaction (preparation of compatibilizer): The PLA-g-MAH grafted masterbatch was prepared in exactly the same way as in step (1) of Example 2.

[0057] (2) Premixing and granulation: Weigh 27.3 parts by weight of PLA-g-MAH grafted masterbatch, 72.7 parts by weight of pure polylactic acid (PLA 4032D), and 9 parts by weight of tannic acid (TA) powder (based on a total weight of 100 parts of PLA-g-MAH and pure PLA, the amount of TA added is 9 parts). The mixing and granulation process parameters are exactly the same as those in step (2) of Example 2.

[0058] (3) Extrusion film formation: The process is exactly the same as step (3) in Example 2, and a 40±5 μm thick MPLA / TA-9% active antioxidant film is finally obtained.

[0059] Comparative Example 1: Pure polylactic acid membrane No tannic acid or PLA-g-MAH compatibilizer was added. 100 parts by weight of polylactic acid (PLA 4032D) were directly fed into a twin-screw extruder for granulation. The temperatures of zones one through nine of the twin-screw extruder were set to 150°C, 155°C, 165°C, 170°C, 165°C, 165°C, 165°C, 160°C, and 155°C, respectively, and the screw speed was 100 r / min. After cooling and pelletizing the extruded strip, it was dried at 70°C for 6 hours to obtain pure PLA masterbatch. Subsequently, the masterbatch was fed into a single-screw casting extruder, and the temperature of each zone of the barrel was set to be the same as in step (3) of Example 1, and the screw speed was 40 r / min. A pure polylactic acid film with a thickness of 40±5 μm was prepared by casting. This film served as the basic performance control group for the active film of this invention.

[0060] Comparative Example 2: High-content TA non-compressor blend membrane (PLA / TA-6%) This comparative example demonstrates the effect of directly adding a higher content of TA without using PLA-g-MAH compatibilizer. 100 parts by weight of polylactic acid (PLA 4032D) and 6 parts by weight of tannic acid (TA) powder were directly mixed. Subsequent melt blending and granulation (process parameters the same as the granulation section of Comparative Example 1) and casting film deposition (process parameters the same as the film deposition section of Comparative Example 1) steps remained unchanged, attempting to prepare a film with a TA content of 6%. However, the experiment found that due to severe phase separation, the film deposition process was extremely difficult, resulting in a rough film surface with pores and TA agglomerates, and significantly deteriorated mechanical properties.

[0061] Performance Testing and Results Analysis The performance of the compatibilizer PLA-g-MAH of the present invention, Examples 1-4, Comparative Example 1, and Comparative Example 2 was characterized, and the key results are as follows: (1) Structural characterization: FTIR analysis: such as Figure 2 As shown, the grafted product PLA-g-MAH was at 1712 cm⁻¹ -1 A new peak appears at 1852 and 1776 cm⁻¹, which is attributed to the asymmetric stretching vibration of C=O in the grafted MAH unit. -1 The disappearance of the characteristic peak of maleic anhydride confirms that MAH was successfully grafted onto the PLA backbone.

[0062] SEM analysis: such as Figure 3 , 4 As shown, the pure PLA membrane has a smooth and dense surface and cross-section. In contrast, the film of Comparative Example 2 (PLA / TA-6%) exhibits a large number of TA agglomerates and pores on its surface, and a rough cross-section with a clear two-phase separation structure. Conversely, the films of Examples 3 (MPLA / TA-6%) and 4 (MPLA / TA-9%) of this invention have uniform and smooth surfaces, dense cross-sections, and TA particles are uniformly dispersed in the PLA matrix at a submicron scale, without obvious agglomeration or interfacial debonding, directly demonstrating the significant compatibilizing effect of PLA-g-MAH.

[0063] (2) Mechanical property testing: The tensile strength (TS) and elongation at break (EAB) of the film were tested according to ASTM D882-12 standard.

[0064] Example 1 (PLA / TA-3%): TS = 37.23 ± 7.77 MPa, EAB = 3.70 ± 1.30% Example 2 (MPLA / TA-3%): TS = 43.73±3.25 MPa, EAB = 3.23±0.39% Example 3 (MPLA / TA-6%): TS = 27.70 ± 3.83 MPa, EAB = 7.93 ± 2.75% Example 4 (MPLA / TA-9%): TS = 10.28 ± 0.32 MPa, EAB = 1.17 ± 0.09% Comparative Example 1 (pure PLA membrane): TS = 51.13 ± 4.53 MPa, EAB = 7.17 ± 1.23% Comparative Example 2 (PLA / TA-6%): TS = 17.29 ± 4.52 MPa, EAB = 1.27 ± 0.05% The results show that although the addition of TA generally reduces the tensile strength of PLA, at the same TA content (6%), the TS and EAB of the film prepared by the method of the present invention (Example 3) are significantly higher than those of the uncompensated direct blend film (Comparative Example 2). In particular, the EAB of Example 3 is even slightly higher than that of the pure PLA film, indicating that the compatibilizing effect of PLA-g-MAH plays a key role in maintaining the toughness of the material. Example 4, due to its high TA content, exhibits a significant decrease in mechanical properties, but it can still be successfully filmed and possesses the basic strength required for application.

[0065] (3) Barrier performance and functional characteristics test: Oxygen Transmission Rate (OTR): Tested at 23°C according to ASTM D1434-82.

[0066] Example 1 (PLA / TA-3%): 348.54±5.73 cm 3 / m 2 24h 0.1MPa Example 2 (MPLA / TA-3%): 285.73±4.20 cm 3 / m 2 24h 0.1MPa Example 3 (MPLA / TA-6%): 393.34 ± 5.14 cm 3 / m 2 24h 0.1MPa Example 4 (MPLA / TA-9%): 433.76 ± 5.14 cm 3 / m 2 24h 0.1MPa Comparative Example 1 (pure PLA membrane): 242.00 ± 3.54 cm 3 / m 2 24h 0.1MPa Comparative Example 2 (PLA / TA-6%): 550.74 ± 12.57 cm 3 / m 2 24h 0.1MPa Water vapor transmission rate (WVP): Tested according to ASTM E96 / E96M-16 at 37.8°C and 100%RH.

[0067] Example 1 (PLA / TA-3%): 175.80±3.10 g / m 2 24h Example 2 (MPLA / TA-3%): 256.50±19.85 g / m 2 24h Example 3 (MPLA / TA-6%): 414.24 ± 12.01 g / m 2 24h Example 4 (MPLA / TA-9%): 572.97 ± 78.21 g / m 2 24h Comparative Example 1 (pure PLA membrane): 176.26 ± 6.86 g / m 2 24h Comparative Example 2 (PLA / TA-6%): 256.79±58.93 g / m 2 24h The introduction of TA increases the OTR of the film, while the addition of MPLA further improves it. This creates a moderately permeable microenvironment inside the packaging, which is beneficial for the respiration of fruits and vegetables and prevents the accumulation of harmful gases. The introduction of TA also increases the WVP of the film, and the addition of MPLA increases the polarity of the film, making it easier for water vapor to permeate and reducing microbial growth. Antioxidant properties: evaluated using DPPH free radical scavenging experiments. Figure 5 As shown, all TA-containing films exhibited significant antioxidant activity. The DPPH scavenging rates of the films in Examples 3 and 4 were both higher than 96%, indicating that TA was effectively maintained at a high activity in the compatibilized system.

[0068] Antibacterial properties: The inhibition rate against Staphylococcus aureus was tested using the thin-film contact method. For example... Figure 6 As shown, the MPLA / TA-9% film exhibits the strongest antibacterial effect, with an inhibition rate exceeding 99%, while the MPLA / TA-6% film also has significant antibacterial activity, superior to the uncompressed low TA content film and pure PLA film.

[0069] (4) Thermal performance test (DSC): DSC analysis showed that the glass transition temperature (Tg) and cold crystallization peak of all films containing TA and PLA-g-MAH were slightly different from those of pure PLA films, but no significant shift in thermal decomposition peak was observed, indicating that the modification process did not seriously damage the thermal stability of the PLA matrix.

[0070] Application example: Test on the preservation effect of peaches The films prepared in Examples 1, 2, 3, and 4 were made into packaging bags and used to package "Bai Feng" peaches of uniform size and ripeness. Comparative Example 1 (pure PLA film) and Comparative Example 2 (PLA / TA-6%) were used as controls, and a separate set of unpackaged samples was used as a blank control (L). All samples were stored at 25±1℃ and 60±3% relative humidity for 12 days, and samples were taken periodically to test various indicators.

[0071] Headspace gas analysis: such as Figure 7 As shown, in Comparative Example 1, the O2 concentration inside the packaging bag dropped to a low level (<2%) by day 6, while CO2 accumulation was severe, leading to accelerated anaerobic respiration and spoilage. In contrast, the film packaging group of the present invention, particularly Example 4, showed a more gradual change in the O2 / CO2 concentration inside the bag, maintaining a more suitable gas ratio.

[0072] Quality Indicators: Weight loss rate: such as Figure 8 As shown, the weight loss rate of Group 4 on day 12 was 8.9%, which was significantly lower than that of the naked group (>15%).

[0073] Hardness: such as Figure 9 As shown, the peaches in Example 4 maintained the best firmness, and were still 20% higher than those in Comparative Example 1 at the end of storage.

[0074] Browning index: such as Figure 10 As shown, browning of peaches in Example 4 was significantly inhibited, with a browning index of only 19.67% on day 12, which was much lower than that of the other groups.

[0075] Microbial growth: such as Figure 11 As shown, the total bacterial count of peaches in Example 4 group increased the slowest, reaching 3.97 log CFU / g on day 12, confirming that the antibacterial activity of the film effectively inhibited spoilage microorganisms.

[0076] Physiological and biochemical indicators: Enzyme activity and oxidative damage: such as Figure 12 , 13 As shown, the polyphenol oxidase (PPO) activity and the accumulation of malondialdehyde (MDA), a lipid peroxidation product, in the peaches of Example 4 were significantly delayed, indicating that the antioxidant activity of the film effectively reduced the oxidative damage to fruit cells.

[0077] Shelf life: Considering all indicators, with sensory unacceptability as the endpoint, the shelf life of Comparative Example 1 was 6 days, while the shelf life of Example 4 of this invention was extended to 12 days, with an extension rate of 100%, demonstrating excellent preservation effect.

Claims

1. A reactive compatibilizing polylactic acid packaging material, characterized in that, It is prepared by a process of blending and melt extrusion of polylactic acid, tannic acid, and a polylactic acid-maleic anhydride graft copolymer. The polylactic acid-maleic anhydride graft copolymer is prepared by a process of blending and melt extrusion of polylactic acid, maleic anhydride, and an initiator.

2. The active polylactic acid packaging material according to claim 1, characterized in that, The active polylactic acid packaging material is in the form of strips, granules, or films.

3. A method for preparing a reactive compatibilizing polylactic acid packaging material, characterized in that, The steps include: Polylactic acid, tannic acid, and polylactic acid graft copolymer with maleic anhydride are blended and melt-extruded to obtain strip-shaped or granular active polylactic acid packaging materials.

4. The preparation method according to claim 3, characterized in that, The preparation of the polylactic acid-maleic anhydride graft copolymer includes: blending polylactic acid, maleic anhydride and an initiator, and then melt-extruding to obtain the polylactic acid-maleic anhydride graft copolymer.

5. The preparation method according to claim 3, characterized in that, It also includes forming granular active polylactic acid packaging materials into films through melt extrusion casting or hot pressing.

6. The active polylactic acid packaging material according to claim 1 or 2, or the active polylactic acid packaging material prepared by the preparation method according to any one of claims 3-5, is used for preparing packaging; or the film-like active polylactic acid packaging material according to claim 2, or the film-like active polylactic acid packaging material prepared by the preparation method according to claim 5, is used for packaging food or flowers.

7. A type of packaging, characterized in that, The packaging material contains the active polylactic acid packaging material according to claim 1 or 2, or the active polylactic acid packaging material prepared by the preparation method according to any one of claims 3-5.

8. The packaging according to claim 7, characterized in that, The packaging can be used to package food or flowers.

9. The packaging according to claim 8, characterized in that, The food is a climacteric food, and the flower is a climacteric flower.

10. The packaging according to claim 7, characterized in that, The packaging is selected from any one of cans, bottles, bags, rolls, boxes, cartons, and films.

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