Mechanical enhanced, antibacterial and antioxidant degradable packaging film as well as preparation method and application thereof

Abstract

The invention belongs to the field of degradable food packaging materials, and particularly relates to a mechanically-enhanced, antibacterial and antioxidant degradable packaging film as well as a preparation method and application thereof. The preparation method specifically comprises the following steps: firstly, constructing porous CaCO3 loaded tea polyphenol functional particles, namely TPs-CaCO3 composite functional particles, and then carrying out melt blending and extrusion blow molding on the TPs-CaCO3 composite functional particles and PBAT / PLA blended resin to prepare the degradable packaging film. Through the synergistic effect of rigidity enhancement of porous CaCO3 and antibacterial and antioxidant functions of TPs, the tensile strength, elongation at break and barrier property of the PBAT / PLA film are remarkably improved, and meanwhile, the film is endowed with long-acting antibacterial and excellent DPPH free radical scavenging capacity. The packaging film can be completely biodegraded, can effectively delay spoilage of perishable food and prolong the shelf life, is simple in preparation process, controllable in cost and suitable for industrial production, solves the dual problems that a traditional food packaging material pollutes the environment and an existing degradable film is single in function, and has important economic, social and ecological benefits.

Description

Technical Field

[0001] This invention belongs to the field of biodegradable food packaging materials, specifically relating to a mechanically reinforced, antibacterial, and antioxidant biodegradable packaging film, its preparation method, and its application, which is particularly suitable for the preservation of perishable foods such as meat, fruits, and vegetables. Background Technology

[0002] Traditional food packaging is mostly passive barrier type, which is difficult to dynamically respond to changes in the food storage microenvironment. Furthermore, commonly used traditional petroleum-based packaging materials such as polyethylene (PE) and polypropylene (PP) are difficult to degrade, causing serious white pollution problems and posing a potential threat to the ecological environment and human health. PBAT (polybutylene adipate-butylene terephthalate) and PLA (polylactic acid), as typical biodegradable polymers, have become ideal choices to replace traditional petroleum-based plastics. PBAT possesses good flexibility and ductility, while PLA has high tensile strength and elastic modulus. However, existing PBAT / PLA composite films still have many technical defects that limit their large-scale application. First, the PBAT / PLA blend system suffers from compatibility issues, making it difficult for the composite film to meet the actual needs of food packaging in terms of tensile strength and elongation at break. Second, it has limited functionality and insufficient barrier properties, lacking antibacterial and antioxidant capabilities, making it difficult to inhibit microbial growth and lipid oxidation. It also has poor barrier effects against oxygen and water vapor, failing to effectively extend the shelf life of food. Finally, existing modification studies mostly focus on improving a single property, and multifunctional synergistic modification schemes that combine mechanical enhancement, barrier optimization, and antibacterial and antioxidant properties are relatively scarce.

[0003] To address the aforementioned issues, researchers have undertaken various modification attempts for PBAT / PLA composite films. CN113801350A describes the chemical modification of polylactic acid with glycidyl methacrylate and cumene peroxide to prepare compatibilizer A. PBAT, PLA, calcium carbonate micropowder, compatibilizer A, and additives are then melt-blended, granulated, and blown into a film. This approach, however, adds excessive fillers, increasing the overall composition while only partially improving the film's mechanical properties. CN107011634A modifies the film using inorganic fillers such as nano-barium sulfate and nano-silica to improve mechanical properties and optical transmittance, while retaining biodegradability. Both methods ultimately enhance the composite material's mechanical and barrier properties or optical properties, but only optimize two aspects, failing to achieve multifunctional synergy. CN114395222A, on the other hand, directly adds cinnamaldehyde and eugenol to the blended membrane without using a carrier. Although the volatile components of plant essential oils achieve antibacterial function, direct addition leads to high loss of cinnamaldehyde during thermal processing. At the same time, the essential oils continue to volatilize during the storage of the finished membrane, resulting in a short period of action.

[0004] Therefore, there is an urgent need to develop a biodegradable packaging film that combines mechanical reinforcement, antibacterial and antioxidant properties, and optimized barrier properties to solve the problems of existing products such as single function, short shelf life, and poor environmental adaptability, while meeting the needs of industrial production and conforming to the trend of green and sustainable development. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing PBAT / PLA composite films, such as insufficient mechanical properties, limited functionality, and limited barrier properties, and to provide a mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film, its preparation method, and its applications. Specifically, it involves melt-blending TPs-CaCO3 composite materials and fully biodegradable resin, followed by extrusion blow molding. The TPs-CaCO3 composite material is prepared by loading tea polyphenols onto porous CaCO3 microspheres. By constructing a porous CaCO3-loaded tea polyphenol functional particle system, the synergistic optimization of mechanical reinforcement, barrier enhancement, and antibacterial and antioxidant functions is achieved, while ensuring the biodegradability and industrial production feasibility of the film, providing an efficient and environmentally friendly packaging solution for the preservation of perishable foods.

[0006] The specific inventive concept of this invention is as follows: (1) Structural design of porous CaCO3: Regular spherical porous CaCO3 with uniform pore size was prepared by starch template method. Its high specific surface area and porous structure can provide sufficient loading sites. At the same time, it can be used as a rigid filler to enhance the mechanical properties of the film and improve the barrier performance through physical barrier effect. The preparation process is simple, low cost, good biocompatibility, and high chemical stability. It can be synthesized on a large scale by precipitation method and is suitable for industrial production. (2) Loading and stability of tea polyphenols (TPs): TPs were loaded on the surface and pores of porous CaCO3. The physical confinement effect of the porous structure and Ca 2+ The coordination with the hydroxyl groups of tea polyphenols improves the thermal stability and dispersibility of TPs, enabling the slow release of TPs, prolonging the antibacterial and antioxidant effects, and extending the shelf life of food.

[0007] The specific technical solution of the present invention is as follows: A mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film, the raw materials of which are, by weight: 90-100 parts of fully biodegradable resin; and 2-10 parts of TPs-CaCO3 composite material.

[0008] The fully biodegradable resin is a mixture of PBAT and PLA, with a mass ratio of PBAT to PLA of (90-95):(5-10). PBAT provides good flexibility and processing performance, while PLA provides high strength. The two are mixed in a specific ratio to achieve complementary mechanical properties. The preferred mass ratio is 95:5.

[0009] The TPs-CaCO3 composite material consists of composite particles formed by loading TPs onto the surface and pores of porous CaCO3, with an average particle size of 1.5-2.5 μm. Tea polyphenols endow the membrane with antibacterial and antioxidant functions. Porous CaCO3 can not only enhance the mechanical and barrier properties of the membrane, but also act as a carrier to realize the slow release of TPs and prolong the action period.

[0010] The final biodegradable packaging film has a thickness of 20-40 μm, preferably 25-35 μm. If the thickness is too thin, the barrier and mechanical properties will be insufficient; if it is too thick, it will increase the cost and hinder degradation. 25-35 μm can balance the requirements of performance and cost.

[0011] The porous CaCO3 in the above scheme is prepared by the following method: Weigh out calcium acetate and ammonium carbonate, with a molar ratio of calcium acetate to ammonium carbonate of (1-1.5):1; dissolve them separately in deionized water to prepare solutions with a concentration of 0.1-0.5 mol / L. Weigh out soluble starch, add deionized water and stir well, then pour into boiling water, boil for 5-10 minutes and cool to obtain a starch solution with a mass fraction of 0.5%-2%, preferably 1.5%. Equal volumes of calcium acetate solution and starch solution were mixed and magnetically stirred at 300-500 rpm for 25-35 min. An equal volume of ammonium carbonate solution was added, and stirring continued for 8-12 min. After standing at room temperature for 10-14 h, the mixture was centrifuged at 5000-8000 rpm for 8-12 min. The collected solid was washed 3-5 times with deionized water. The washed solid was dried at 60-80℃ for 8-12 h, and then ground to obtain porous CaCO3 powder with an average particle size of 1.5-2.5 μm. Testing showed that the pore size range of the porous CaCO3 powder was 10-30 nm, facilitating subsequent processing.

[0012] The preparation method of the TPs-CaCO3 composite material includes the following steps: Weigh the above porous CaCO3 powder and add it to deionized water at a solid-liquid ratio of 1 g: 40-60 mL. Disperse the mixture ultrasonically at 150-250 W for 15-25 min. Then add tea polyphenols at a mass ratio of (0.25-1): 1. Stir magnetically at 25-35 ℃ and 200-400 rpm for 20-28 h. Vacuum dry at 60-70 ℃ for 10-14 h to obtain TPs-CaCO3 composite material.

[0013] This invention further provides a method for preparing the above-mentioned mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film, specifically including the following steps: Step 1: The fully biodegradable resin particles and TPs-CaCO3 composite materials are vacuum dried at 75-85 ℃ for 10-14 h with a vacuum degree of -0.08 to -0.1 MPa to remove moisture from the materials.

[0014] Step 2: Add the dried fully biodegradable resin and TPs-CaCO3 composite material to a high-speed mixer according to the ratio, and mix at 2000-3000 rpm for 6-10 minutes.

[0015] Step 3: Add the mixture obtained in Step 2 into a twin-screw extruder at a feed rate of 80-180 g / min. Set the temperatures of the five zones from the feed inlet to the extruder head as follows: 160-170℃, 165-175℃, 170-180℃, 165-175℃, and 160-170℃, respectively. Set the screw speed to 30-40 rpm. After melt blending, the material is extruded from the die head, air-dried, and then granulated in a pelletizer to obtain composite masterbatch.

[0016] Step 4: Vacuum dry the composite masterbatch at 75-85℃ for 10-14 h, then feed it into a single-screw extruder. Set the temperatures of the four zones from the feed inlet to the die head as follows: 155-165℃, 160-170℃, 165-175℃, and 160-170℃, respectively. The screw speed is 30-50 rpm. After melt extrusion, the material is blown into a film using a blown film extruder. The traction rate is 20-40 Hz, the blower speed is 40-60 Hz, and the take-up rate is 10-20 Hz. After cooling and setting, the film is wound up and stored at low temperature for later use.

[0017] The fully biodegradable resin particles are a mixture of PBAT particles and PLA particles, with a particle size of 2-4 mm.

[0018] The mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film provided by this invention can be widely used for the preservation of perishable foods such as meat, fruits and vegetables, and edible fungi.

[0019] Compared with the prior art, the present invention has the following beneficial effects: Calcium carbonate, as an inorganic filler, has advantages such as low preparation cost, good biocompatibility, and environmental friendliness. However, commercially available nano-calcium carbonate can only achieve surface adsorption and cannot load active substances to achieve long-term sustained-release function. Tea polyphenols (TPs) are natural polyphenols extracted from tea leaves, possessing broad-spectrum antibacterial and strong antioxidant properties. They have significant inhibitory effects on foodborne pathogens such as Escherichia coli and Staphylococcus aureus, and can scavenge free radicals and delay lipid oxidation. However, tea polyphenols have a low decomposition temperature, and the melt processing of PBAT / PLA can lead to the degradation of some tea polyphenols, reducing their effectiveness. Secondly, tea polyphenols have a polyhydroxy structure and are hydrophilic substances, resulting in poor compatibility with the hydrophobic PBAT / PLA matrix, affecting the mechanical properties and uniformity of the film. Based on the properties of the aforementioned raw materials, the inventors loaded tea polyphenols onto porous CaCO3 to obtain TPs-CaCO3 composite materials. Unlike traditional inorganic nanocarriers, the preparation method of the resulting porous CaCO3 is simple, and the pore size can be adjusted by stirring speed, starch solution concentration, and solution molar ratio, making it suitable for various antibacterial and antioxidant functional receptors. Simultaneously, multifunctional synergistic optimization improves membrane performance, with tensile strength and elongation at break increasing by up to 30% and 20% respectively compared to PBAT / PLA membranes, meeting the requirements for stretching, folding, and transportation in food packaging. The resulting packaging film exhibits strong antioxidant capacity and high DPPH free radical scavenging rate, effectively delaying lipid oxidation in food.

[0020] This invention employs an extrusion blow molding process, requiring no special equipment and compatible with existing plastic film production equipment. It features low raw material costs, simple synthesis, and zero waste emissions during production, meeting green production requirements and enabling large-scale industrial production. The food packaging film of this invention can be used for preservation packaging of various perishable foods such as meat, fruits, vegetables, and aquatic products, as well as for protective packaging during food transportation and storage, showing broad market application prospects. Attached Figure Description

[0021] Figure 1 These are the mechanical property results of the packaging films prepared in Examples 1-4 and Comparative Examples 1-3; Figure 2 These are the water-blocking performance results of the packaging films prepared in Examples 1-4 and Comparative Examples 1-3; Figure 3 These are graphs showing the gas barrier properties of the packaging films prepared in Examples 1-4 and Comparative Examples 1-3; Figure 4 These are graphs showing the antibacterial properties of the packaging films prepared in Examples 1-4 and Comparative Examples 1-3; Figure 5 These are the results of the antioxidant properties of the packaging films prepared in Examples 1-4 and Comparative Examples 1-3; Figure 6 This is a graph showing the cumulative release results of the packaging films prepared in Examples 1-4 and Comparative Example 3; Figure 7 These are photographs showing the preservation effect of the packaging films prepared in Examples 1-4 and Comparative Examples 1-3 on fresh chicken breast stored at 4 ℃ for different times. Detailed Implementation

[0022] The technical solution of the present invention will be further described below with reference to specific embodiments. These embodiments are only used to illustrate the technical solution of the present invention in more detail and should not be construed as limiting the scope of protection of the present invention.

[0023] Unless otherwise specified, all reagents used in the following examples are commercially available.

[0024] Example 1: A method for preparing a mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film. The specific steps for preparing porous CaCO3 are as follows: First, 15.8 g of calcium acetate and 9.6 g of ammonium carbonate were weighed and added separately to 1000 mL of deionized water. 15.22 g of soluble starch was weighed, added to 50 mL of deionized water, stirred well, and then poured into 950 mL of boiling water and boiled for 5 min. Next, 1000 mL of calcium acetate solution and 1000 mL of starch solution were mixed and magnetically stirred at 400 rpm for 30 min. An equal volume of ammonium carbonate solution was added and stirring continued for 10 min. After standing at room temperature for 12 h, the mixture was centrifuged at 6800 rpm for 10 min, and the solid was collected and washed three times with deionized water. The washed solid was vacuum dried at 70 ℃ for 10 h and then ground with a grinding wheel to obtain approximately 5 g of porous CaCO3 powder. The average particle size of the powder was 1.64 μm, and the pore size range of the particles was 10-30 nm.

[0025] The specific steps for preparing TPs-CaCO3 composite materials are as follows: 5g of porous CaCO3 powder was weighed and added to 200 mL of deionized water, and ultrasonically dispersed at 200 W for 20 min. Then, 2.5g of tea polyphenols were added, and the mixture was magnetically stirred at 25 ℃ and 400 rpm for 24 h; it was then dried at 65 ℃ for 12 h to obtain the TPs-CaCO3 composite material.

[0026] The specific steps for preparing a mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film are as follows: The PBAT, PLA, and TPs-CaCO3 composite material was vacuum dried at 80 °C for 12 h. The dried PBAT, PLA, and TPs-CaCO3 composite material was then added to a high-speed mixer at a weight ratio of 95:5:2 and mixed at 3000 rpm for 10 min. The mixture was then fed into a twin-screw extruder at a feed rate of 80-180 g / min. The temperatures of the five zones from the feed inlet to the extruder die head were set sequentially to 165 °C, 170 °C, 175 °C, 170 °C, and 165 °C, with a screw speed of 35 rpm. After melt blending, the material was extruded from the die head, naturally air-dried, and then granulated in a pelletizer at a speed of 25 rpm to obtain composite masterbatch.

[0027] The composite masterbatch was vacuum dried at 80 ℃ for 12 h and then fed into a single-screw extruder. The temperatures of the four zones from the feed inlet to the die head were set to 160 ℃, 165 ℃, 170 ℃, and 165 ℃ respectively, and the screw speed was 40 rpm. After melt extrusion, the material was blown into a film by a blown film extruder with a traction rate of 20 Hz, a blower speed of 50 Hz, and a take-up rate of 20 Hz.

[0028] The obtained mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film was sealed in a black opaque plastic bag and stored in a dry, cool, and dark place; the thickness of the mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film was controlled between 31±1 μm.

[0029] Example 2: A method for preparing a mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film. The specific steps for preparing porous CaCO3 are as follows: First, 17.2 g of calcium acetate and 9.9 g of ammonium carbonate were weighed and added separately to 1000 mL of deionized water. 16 g of soluble starch was weighed, added to 50 mL of deionized water, stirred well, and then poured into 950 mL of boiling water and boiled for 5 min. Next, 1000 mL of calcium acetate solution and 1000 mL of starch solution were mixed and magnetically stirred at 400 rpm for 30 min. An equal volume of ammonium carbonate solution was added and stirring continued for 10 min. After standing at room temperature for 12 h, the mixture was centrifuged at 6800 rpm for 10 min, and the solid was collected and washed three times with deionized water. The washed solid was vacuum dried at 70 ℃ for 10 h and then ground to obtain porous CaCO3 powder. The average particle size of the powder was 1.72 μm, and the pore size range of the particles was 10-30 nm.

[0030] The specific steps for preparing TPs-CaCO3 composite materials are as follows: 7 g of porous CaCO3 powder was weighed and added to 350 mL of deionized water, and ultrasonically dispersed at 200 W for 20 min. 5 g of tea polyphenols were added, and the mixture was magnetically stirred at 25 ℃ and 400 rpm for 24 h. The mixture was then dried at 70 ℃ for 12 h to obtain the TPs-CaCO3 composite material.

[0031] The specific steps for preparing a mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film are as follows: The PBAT, PLA, and TPs-CaCO3 composite material was vacuum dried at 80 ℃ for 12 h at a vacuum degree of -0.1 MPa. The dried PBAT, PLA, and TPs-CaCO3 composite material was then added to a high-speed mixer at a weight ratio of 95:5:3 and mixed at 3000 rpm for 10 min. The mixture was then fed into a twin-screw extruder at a feed rate of 80-180 g / min. The temperatures of the five zones from the feed inlet to the extruder die head were set sequentially to 165 ℃, 170 ℃, 175 ℃, 170 ℃, and 165 ℃, with a screw speed of 35 rpm. After melt blending, the material was extruded from the die head, naturally air-dried, and then granulated in a pelletizer at a speed of 25 rpm to obtain composite masterbatch.

[0032] The composite masterbatch was vacuum dried at 80 ℃ for 12 h and then fed into a single-screw extruder. The temperatures of the four zones from the feed inlet to the die head were set to 160 ℃, 165 ℃, 170 ℃, and 165 ℃ respectively, and the screw speed was 40 rpm. After melt extrusion, the material was blown into a film by a blown film extruder with a traction rate of 20 Hz, a blower speed of 50 Hz, and a take-up rate of 20 Hz.

[0033] The obtained mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film was sealed in a black opaque plastic bag and stored in a dry, cool, and dark place; the thickness of the mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film was controlled between 33±1μm.

[0034] Example 3: A method for preparing a mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film. The specific steps for preparing porous CaCO3 are as follows: First, 18.4 g of calcium acetate and 10.2 g of ammonium carbonate were weighed and added separately to 1000 mL of deionized water. 13.9 g of soluble starch was weighed, added to 50 mL of deionized water, stirred well, and then poured into 950 mL of boiling water and boiled for 5 min. Next, 1000 mL of calcium acetate solution was mixed with 1000 mL of starch solution and magnetically stirred at 400 rpm for 30 min. Then, an equal volume of ammonium carbonate solution was added to the calcium acetate solution and stirred for another 10 min. After standing at room temperature for 12 h, the mixture was centrifuged at 6800 rpm for 10 min, and the solid was collected and washed three times with deionized water. The washed solid was vacuum dried at 70 ℃ for 10 h and then ground to obtain porous CaCO3 powder. The average particle size of the powder was 2.11 μm, and the pore size range of the particles was 10-30 nm.

[0035] The specific steps for preparing TPs-CaCO3 composite materials are as follows: 8.6 g of porous CaCO3 powder was weighed and added to 430 mL of deionized water, and ultrasonically dispersed at 200 W for 20 min. 7.5 g of tea polyphenols were added, and the mixture was magnetically stirred at 25 ℃ and 400 rpm for 24 h; then dried at 70 ℃ for 12 h to obtain the TPs-CaCO3 composite material.

[0036] The specific steps for preparing a mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film are as follows: The PBAT, PLA, and TPs-CaCO3 composite material was vacuum dried at 80 ℃ for 12 h at a vacuum degree of -0.1 MPa. The dried PBAT, PLA, and TPs-CaCO3 composite material was then added to a high-speed mixer at a weight ratio of 95:5:4 and mixed at 3000 rpm for 10 min. The mixture was then fed into a twin-screw extruder at a feed rate of 80-180 g / min. The temperatures of the five zones from the feed inlet to the extruder die head were set sequentially to 165 ℃, 170 ℃, 175 ℃, 170 ℃, and 165 ℃, with a screw speed of 35 rpm. After melt blending, the material was extruded from the die head, air-dried, and then granulated in a pelletizer at a speed of 25 rpm to obtain composite masterbatch.

[0037] The composite masterbatch was vacuum dried at 80 ℃ for 12 h and then fed into a single-screw extruder. The temperatures of the four zones from the feed inlet to the die head were set to 160 ℃, 165 ℃, 170 ℃, and 165 ℃ respectively, and the screw speed was 40 rpm. After melt extrusion, the material was blown into a film by a blown film extruder with a traction rate of 20 Hz, a blower speed of 50 Hz, and a take-up rate of 20 Hz.

[0038] The obtained mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film was sealed in a black opaque plastic bag and stored in a dry, cool, and dark place; the thickness of the mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film was controlled between 35±1 μm.

[0039] Example 4: A method for preparing a mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film. The specific steps for preparing porous CaCO3 are as follows: First, 19.8 g of calcium acetate and 11.6 g of ammonium carbonate were weighed and added separately to 1000 mL of deionized water. 10 g of soluble starch was weighed, added to 50 mL of deionized water, stirred well, and then poured into 950 mL of boiling water and boiled for 5 min. Next, 1000 mL of calcium acetate solution and 1000 mL of starch solution were mixed and magnetically stirred at 400 rpm for 30 min. An equal volume of ammonium carbonate solution was added and stirring continued for 10 min. After standing at room temperature for 12 h, the mixture was centrifuged at 6800 rpm for 10 min, and the solid was collected and washed three times with deionized water. The washed solid was vacuum dried at 70 ℃ for 10 h and then ground to obtain porous CaCO3 powder. The average particle size of the powder was 2.42 μm, and the pore size range of the particles was 10-30 nm.

[0040] The specific steps for preparing TPs-CaCO3 composite materials are as follows: 13.5 g of porous CaCO3 powder was weighed and added to 650 mL of deionized water, and ultrasonically dispersed at 200 W for 20 min. 10 g of tea polyphenols were added, and the mixture was magnetically stirred at 25 ℃ and 400 rpm for 24 h; then dried at 70 ℃ for 12 h to obtain the TPs-CaCO3 composite material.

[0041] The specific steps for preparing a mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film are as follows: The PBAT, PLA, and TPs-CaCO3 composite material was vacuum dried at 80 ℃ for 12 h at a vacuum degree of -0.1 MPa. The dried PBAT, PLA, and TPs-CaCO3 composite material was then added to a high-speed mixer at a weight ratio of 95:5:5 and mixed at 3000 rpm for 10 min. The mixture was then fed into a twin-screw extruder at a feed rate of 80-180 g / min. The temperatures of the five zones from the feed inlet to the extruder die head were set sequentially to 165 ℃, 170 ℃, 175 ℃, 170 ℃, and 165 ℃, with a screw speed of 35 rpm. After melt blending, the material was extruded from the die head, naturally air-dried, and then granulated in a pelletizer at a speed of 25 rpm to obtain composite masterbatch.

[0042] The composite masterbatch was vacuum dried at 80 ℃ for 12 h and then fed into a single-screw extruder. The temperatures of the four zones from the feed inlet to the die head were set to 160 ℃, 165 ℃, 170 ℃, and 165 ℃ respectively, and the screw speed was 40 rpm. After melt extrusion, the material was blown into a film by a blown film extruder with a traction rate of 20 Hz, a blower speed of 50 Hz, and a take-up rate of 20 Hz.

[0043] The obtained mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film was sealed in a black opaque plastic bag and stored in a dry, cool, and dark place; the thickness of the mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film was controlled between 37±1 μm.

[0044] Comparative Example 1 The biodegradable packaging film was prepared using the same steps as in Example 1, except that no TPs-CaCO3 composite material was added in Comparative Example 1. PBAT and PLA were mixed at a mass ratio of 95:5 and fed into the feed inlet of a twin-screw extruder. Other steps were the same as in Example 1.

[0045] Comparative Example 2 Mechanically reinforced biodegradable packaging film was prepared using the same steps as in Example 1. The difference was that in Comparative Example 2, porous CaCO3 was used directly as the barrier material. PBAT, PLA, and porous CaCO3 were mixed in a mass ratio of 95:5:5 and then fed into the feed inlet of a twin-screw extruder. Other steps were the same as in Example 1.

[0046] Comparative Example 3 The antibacterial, antioxidant, and biodegradable packaging film was prepared using the same steps as in Example 1. The difference was that in Comparative Example 3, tea polyphenols were used directly as the antibacterial substance. PBAT, PLA, and tea polyphenols were mixed in a mass ratio of 95:5:5 and then fed into the feed inlet of a twin-screw extruder. The other steps were the same as in Example 1.

[0047] Experimental Example 1: Mechanical Property Testing The biodegradable packaging films prepared in Examples 1-4 and Comparative Examples 1-3 were subjected to mechanical property tests. The test methods were in accordance with GB 13022-91. The results are shown below. Figure 1 , Figure 1 The graph shows the tensile strength / nominal strain at break.

[0048] The results showed that, compared with Comparative Examples 1 and 3, Examples 1-4 and Comparative Example 2 all improved the mechanical properties of the food preservation film, indicating that CaCO3, as a rigid inorganic filler, improved the toughness of the film. The optimal overall performance was achieved under the conditions of Example 3: the tensile strength reached 37.41 MPa, an increase of 15.6% compared to Comparative Example 2; at the same time, the elongation at break remained at a relatively high level of 530.7%, achieving a good balance between high strength and high toughness.

[0049] Experiment Example 2 Barrier Performance Test The biodegradable packaging films prepared in Examples 1-4 and Comparative Examples 1-3 were subjected to barrier performance tests. The moisture permeability (WVT) and water permeability (WVP) of the composite films were tested using an automated moisture permeability tester. The cupping method was employed, with the film cut into 33 cm² pieces using a cutting tool. 2 A circular sample membrane was prepared. The experimental temperature was 38 ℃, the experimental humidity was 90% RH, and the preheating time was 1 h. The results are shown in [Figure number missing]. Figure 2 The O2 and CO2 permeability of the composite membrane was tested using a differential pressure gas permeation apparatus. The membrane was cut into pieces with an area of ​​38.48 cm². 2 A circular slice was used to seal the sample in the middle of the test chamber. After the system stabilized, various barrier parameters were recorded. The results are shown in [the table below]. Figure 3 .

[0050] The results show that, compared with Comparative Examples 1 and 3, Examples 1-4 and Comparative Example 2 have better water-blocking effects. This indicates that some water vapor is absorbed after entering the pores due to the porous structure of CaCO3, resulting in the lowest WVT and WVP in Comparative Example 2; some water vapor moves along a longer path on the outside of the porous spherical membrane, leading to better membrane barrier performance. Compared with Comparative Example 1, Examples 1-4 and Comparative Examples 2-3 all have a gas-blocking effect.

[0051] Experiment Example 3: Antibacterial Performance Test Referring to GB / T 31402-2023 and making modifications, the biodegradable packaging films prepared in Examples 1-4 and Comparative Examples 1-3 were tested for antibacterial properties using the plate count method. Common Escherichia coli and Staphylococcus aureus were cultured at 37 °C for 24 h and diluted to 10 μL / mL. 6 One colony-forming unit (CFU). 50 mg of the films from Examples 1-4 and Comparative Examples 1-3 were co-cultured with 1 mL of diluted bacterial solution for 4 h. Then, 100 μL of the above bacterial solution was dropped onto an AGAR plate, spread evenly with a sterilized spreader, and inverted to incubate at 37 ℃ for 12 h. Results are shown in the figure. Figure 4 .

[0052] The results showed that, compared with Comparative Examples 1 and 2, Examples 1-4 and Comparative Example 3 had antibacterial properties. Among them, Examples 3, 4 and Comparative Example 3 had superior antibacterial ability compared with the others, indicating that the composite material with added tea polyphenols can significantly improve the antibacterial properties of the film and show better antibacterial effect.

[0053] Experiment Example 4: Antioxidant Performance Test 25 mg of the biodegradable packaging films prepared in Examples 1-4 and Comparative Examples 1-3 were added to three different 5 mL food simulants (H2O, simulating aqueous foods such as fresh fruits, vegetables, and beverages; 10% C2H5OH, simulating low-oil and low-fat foods; and 50% C2H5OH, simulating medium-oil and medium-fat foods), respectively, and reacted in the dark for 2 h. The soaking solution was then reacted with DPPH solution for 1 h to form the experimental group. An equal volume of solution and anhydrous ethanol served as the blank group, and an equal volume of H2O and DPPH solution served as the control group. The absorbance of the supernatant at 517 nm was measured, the scavenging rate was calculated, and the antioxidant performance was evaluated. The results are shown in [Figure number missing]. Figure 5 .

[0054] The results showed that Examples 1-4 and Comparative Example 3 all exhibited antioxidant capacity, with Example 3 showing slightly higher antioxidant capacity than Comparative Example 3. This confirms that the TPs-CaCO3 loading structure improved the retention rate of TPs and the antioxidant effect.

[0055] Experiment Example 5: Accelerated Release Test TPs were dissolved in H2O to prepare solutions with concentrations of 5, 10, 20, 25, 30, 35, 40, and 45 μg / mL. A standard curve was plotted based on the absorbance at 280 nm. 100 mg of the composite film from Examples 1-4 and Comparative Example 3 was weighed and immersed in 30 mL of H2O. The solution was shaken in a constant-temperature shaker at 37 °C in the dark. 2 mL samples were taken at 0.5, 1, 3, 4, 7, 10, 12, 24, 48, 72, 96, and 120 h, and an equal volume of fresh solution was added. The absorbance at 280 nm was measured, and the cumulative release rate was calculated based on the standard curve. The results are shown in [Figure number missing]. Figure 6 .

[0056] The results showed that Comparative Example 3 reached a cumulative release rate of approximately 76.1% within 12 hours, then rapidly entered a plateau phase, exhibiting typical "burst release" characteristics. In contrast, the biodegradable packaging films of Examples 1-4 all demonstrated significant sustained-release behavior, with Example 3 achieving a cumulative release rate of 80.1% at 120 hours, extending the release period by more than 10 times. This sustained-release mechanism effectively overcomes the shortcomings of directly adding TPs, such as excessively high initial concentrations and insufficient protection in the later stages, enabling the packaging material to continuously and stably release active ingredients throughout the entire shelf life.

[0057] Experiment Example 6: Fresh Chicken Breast Preservation Test The biodegradable packaging films prepared in Examples 1-4 and Comparative Examples 1-3 were used for fresh chicken breast preservation tests. Fresh chicken breasts were washed with sterile deionized water and dried. Samples were cut into approximately 60 g pieces and wrapped with the biodegradable packaging films prepared in Examples 1-4 and Comparative Examples 1-3. The samples were then stored in a refrigerated environment at 4 ℃. Samples were taken every 48 hours, and their appearance was observed and photographed. The results are shown in the table below. Figure 7The initiation of browning has been marked.

[0058] The results showed that the chicken breast wrapped in Comparative Examples 1 and 2 exhibited oxidation and browning on the surface after 2 days. Examples 1-4 and Comparative Example 3 all extended the shelf life to varying degrees. With increasing shelf life, Examples 1-4 and Comparative Example 3 demonstrated an effect of extending the shelf life of chicken breast.

[0059] The above experiments show that, based on comprehensive performance analysis, Example 3 exhibits better mechanical properties, high CO2 permeability, low water vapor permeability, and good antibacterial and antioxidant properties, effectively preserving food. The composite packaging film prepared in Example 3 of this invention demonstrates significant advantages in overall performance: it achieves an optimal balance between mechanical strength and toughness; its DPPH free radical scavenging rate reaches 92%, resulting in optimal antibacterial performance; and, combined with a moderately permeable oxygen and carbon dioxide-generated modified atmosphere microenvironment, it overcomes the shortcomings of directly added functional components, such as easy burst release and poor functional persistence.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any equivalent substitutions or modifications made by those skilled in the art within the spirit and principle of the present invention without any creative effort should be included within the protection scope of the present invention.

Claims

1. A mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film, characterized in that, The raw materials, by weight, are: fully biodegradable resin: 90-100 parts; TPs-CaCO3 composite material: 2-10 parts; The fully biodegradable resin is a mixture of PBAT and PLA, with a mass ratio of PBAT to PLA of (90-95):(5-10). The TPs-CaCO3 composite material is a composite particle formed by TPs loaded on the surface and pores of porous CaCO3, with an average particle size of 1.5-2.5 μm.

2. The mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film according to claim 1, characterized in that, The mass ratio of PBAT to PLA is 95:

5.

3. The mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film according to claim 1, characterized in that, The thickness of the biodegradable packaging film is 20-40 μm.

4. The mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film according to claim 1, characterized in that, The porous CaCO3 was prepared by the following method: Weigh out calcium acetate and ammonium carbonate, with a molar ratio of calcium acetate to ammonium carbonate of (1-1.5):1; dissolve them separately in deionized water to prepare solutions with a concentration of 0.1-0.5 mol / L. Weigh out soluble starch, add deionized water and stir well, then pour into boiling water, boil for 5-10 minutes and let cool to obtain a starch solution with a mass fraction of 0.5%-2%. Mix equal volumes of calcium acetate solution and starch solution, and magnetically stir at 300-500 rpm for 25-35 min. Add an equal volume of ammonium carbonate solution to the calcium acetate solution and continue stirring for 8-12 min. Let stand at room temperature for 10-14 h, then centrifuge at 5000-8000 rpm for 8-12 min. Collect the solid and wash it 3-5 times with deionized water. Dry the washed solid at 60-80℃ for 8-12 h. After washing, grind to obtain porous CaCO3 powder with an average particle size of 1.5-2.5 μm.

5. The mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film according to claim 1 or 4, characterized in that, The TPs-CaCO3 composite material was prepared by the following method: Weigh the above porous CaCO3 powder and add it to deionized water at a solid-liquid ratio of 1 g: 40-60 mL. Disperse the mixture ultrasonically at 150-250 W for 15-25 min. Then add tea polyphenols at a mass ratio of (0.25-1):

1. Stir magnetically at 25-35℃ and 200-400 rpm for 20-28 h. Vacuum dry at 60-70℃ for 10-14 h to obtain TPs-CaCO3 composite material.

6. The method for preparing the mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film according to claim 1, characterized in that, Specifically, the following steps are included: Step 1: The fully biodegradable resin particles and TPs-CaCO3 composite materials are vacuum dried at 75-85 ℃ for 10-14 h with a vacuum degree of -0.08 to -0.1 MPa to remove moisture from the materials. Step 2: Add the dried fully biodegradable resin and TPs-CaCO3 composite material to a high-speed mixer according to the ratio, and mix at 2000-3000 rpm for 6-10 minutes; Step 3: Add the mixture obtained in Step 2 into a twin-screw extruder at a feed rate of 80-180 g / min. Set the temperatures of the five zones from the feed inlet to the extruder head as follows: 160-170℃, 165-175℃, 170-180℃, 165-175℃, and 160-170℃, respectively. Set the screw speed to 30-40 rpm. After melt blending, the material is extruded from the die head, air-dried, and then granulated in a pelletizer to obtain composite masterbatch. Step 4: Vacuum dry the composite masterbatch at 75-85℃ for 10-14 h, then feed it into a single-screw extruder. Set the temperatures of the four zones from the feed inlet to the die head as follows: 155-165℃, 160-170℃, 165-175℃, and 160-170℃, respectively. The screw speed is 30-50 rpm. After melt extrusion, the material is blown into a film using a blown film extruder. The traction rate is 20-40 Hz, the blower speed is 40-60 Hz, and the take-up rate is 10-20 Hz. After cooling and setting, the film is wound up and stored at low temperature for later use.

7. The preparation method according to claim 6, characterized in that, The fully biodegradable resin particles are a mixture of PBAT particles and PLA particles, with a particle size of 2-4 mm.

8. The application of the mechanically reinforced, antibacterial, antioxidant, and biodegradable packaging film as described in claim 1 as a food packaging film.

9. The application according to claim 8, characterized in that, Packaging for preserving meat and fruit / vegetable products.

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