Biodegradable plastic bag for apple packaging and method for preparing the same

Abstract

The application discloses a biodegradable apple packaging plastic bag and a preparation method thereof, and relates to the technical field of plastic bag preparation.The plastic bag comprises the following component raw materials: polyethylene grafted maleic anhydride, a toughening agent, modified corn starch, modified biochar, an anti-fog agent, epsilon-polylysine and a composite additive.In the application, the modified corn starch is a modified material with the functions of degradation acceleration, antibacterial enhancement and mechanical reinforcement, and can form a carbon source available for microorganisms in the film after being added, so that the degradation process of the polyethylene grafted maleic anhydride, polyhexanedioic acid and terephthalic acid butylene butylene matrix is promoted, and the degradation period in the natural environment is shortened.The chitosan oligosaccharide component can play a high-efficiency antibacterial role and cooperatively improve the antibacterial and fresh-keeping effect of the packaging together with other antibacterial components.The nano-cellulose can construct a molecular support network and make up for the problem of the decrease of the mechanical properties of the film possibly caused by the addition of the starch.

Description

Technical Field

[0001] This invention relates to the field of plastic bag manufacturing technology, and in particular to a biodegradable apple packaging plastic bag and its manufacturing method. Background Technology

[0002] Plastic bags are lightweight and flexible containers made primarily of high molecular polymers. They are characterized by their extremely light weight, low cost, waterproofness, and durability. Since their widespread adoption in the mid-20th century, they have become one of the most common packaging items in the world.

[0003] Traditional biodegradable apple packaging suffers from numerous shortcomings, including long degradation cycles and environmental defects due to difficulty in rapid and complete decomposition in natural environments; mechanical deficiencies such as an imbalance between rigidity and toughness and weak tear and puncture resistance; practical pain points such as a lack of integrated anti-fogging, antibacterial, and preservation functions, leading to easy mold and rot, damage to appearance, and short shelf life; safety hazards due to reliance on non-food-grade additives and migration risks in some products; technological challenges such as poor melt flowability, unstable film bubbles, and difficulty in large-scale production during processing; and industrial limitations such as single raw materials, lack of utilization of agricultural waste, high production costs, and low resource recycling rates. Based on these limitations, this invention provides a biodegradable apple packaging plastic bag and its preparation method. Summary of the Invention

[0004] The main objective of this invention is to provide a biodegradable apple packaging plastic bag with low apple rot rate and high antibacterial rate against Escherichia coli, which is applied in a biodegradable apple packaging plastic bag and its preparation method.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a biodegradable apple packaging plastic bag, which comprises the following raw materials: 58-65 parts of polyethylene grafted maleic anhydride, 20-28 parts of toughening agent, 2-3 parts of modified corn starch, 2-3 parts of modified biochar, 0.8-1.2 parts of antifogging agent, 0.2-0.4 parts of ε-polylysine, and 1-1.5 parts of composite additives; The maleic anhydride grafting rate of polyethylene grafted with maleic anhydride is 0.5-2.0%, and the residual maleic anhydride content is ≤0.5%. It can gradually decompose into harmless substances in natural environments such as compost and soil, fundamentally solving the environmental pollution problem of traditional plastic packaging. The grafting groups in its molecular structure can form a stable bond with polar fillers such as modified corn starch and modified biochar, significantly improving the compatibility of each component, preventing material delamination or agglomeration, and ensuring a uniform and stable packaging structure.

[0006] ε-Polylysine is a functional additive that supplements and enhances the antibacterial properties of packaging. It has a broad antibacterial spectrum and significantly inhibits microorganisms such as Escherichia coli and Penicillium that cause apple mold, effectively reducing the rate of apple decay during storage. This antibacterial agent is a natural microbial fermentation product with high food-grade safety and will not have adverse effects on human health or apple quality. At the same time, it has excellent thermal stability and is not easily decomposed or inactivated during the high-temperature processing of blending and granulation, thus maintaining the antibacterial activity of the packaging for a long time.

[0007] The antifogging agent is a mixture of triglyceride monostearate and Span 60; The mass ratio of the triglyceride monostearate to Span 60 is 3:2.

[0008] Anti-fogging agent is a special additive that solves the problem of fogging on the inner wall of apple packaging bags. After being added, it can reduce the surface tension of the film, allowing water vapor inside the bag to spread evenly into a water film, preventing fog droplets from obscuring the appearance of the apple and improving the product display effect. This anti-fogging agent is an internal additive, requiring no additional coating process. It works synergistically with the hydrophilic groups of modified biochar, resulting in a more durable and stable anti-fogging effect, and its ingredients are biodegradable.

[0009] Furthermore, the toughening agent is either polyadipate or butylene terephthalate.

[0010] Poly(di(2- ...3-2-di(2-di(2-di(2-di(2-di(2-di(2-di(2-di(2-di(2-3-3))))))))))))))))))))))))))))))))))) terephthalic acid)'s degradation method 1) and 2-di(2-di(2-di(2-di(2-di(2-di(2-di(2-di(2-di(2-di(2-di(2-di(2-di(2-di(2-di(2-di(2-di

[0011] Furthermore, the composite additive is composed of maleic anhydride-grafted polypropylene, calcium stearate, and triglycerides. The mass ratio of maleic anhydride-grafted polypropylene, calcium stearate, and triglycerides is 3:2:1.

[0012] Furthermore, the preparation of the modified corn starch includes the following steps: A1. Mix chitosan oligosaccharide and deionized water, disperse using an ultrasonic disperser, set the power to 800W, disperse for 8 minutes to obtain chitosan oligosaccharide solution; A2. Mix nanocellulose and deionized water, disperse using an ultrasonic disperser, set the power to 800W, disperse for 8 minutes to obtain a cellulose solution; A3. Add corn starch to a high-speed mixer, then add chitosan oligosaccharide solution and cellulose solution in sequence and stir. Set the speed to 2000 rpm and the temperature to ≤40℃. Stir for 30 minutes to obtain a suspension. A4. Place the suspension into a spray dryer for drying, set the inlet air temperature to 160℃, the outlet air temperature to 80℃, the feed rate to 50mL / min, and the atomization pressure to 0.3MPa, to obtain modified corn starch.

[0013] Furthermore, the mass ratio of chitosan oligosaccharide to deionized water in A1 is 1:15; The mass ratio of nanocellulose to deionized water in A2 is 1:16.

[0014] Furthermore, the mass ratio of the corn starch, chitosan oligosaccharide solution, and cellulose solution is 8:1:1.

[0015] The corn starch is food grade, with an amylose content of ≥25% and a moisture content of ≤12%.

[0016] Chitosan oligosaccharide has a degree of deacetylation ≥90%, is food grade, and has a molecular weight of 5000-10000.

[0017] The diameter of nanocellulose is 20-30 nm and the length is 500-800 nm.

[0018] Furthermore, the preparation of the modified biochar includes the following steps: B1. Crush the apple pomace to a particle size of 5-10mm, dry it with hot air at a temperature of 60℃ for 4 hours to obtain dried apple pomace; B2. Mix malic acid, ε-polylysine, zinc acetate, glycerol and deionized water and stir at 300 rpm for 15 minutes to obtain the modified solution; B3. Mix the dried apple pomace and the modified liquid, stirring for 3-5 minutes every 30 minutes, and mix for 3 hours to obtain a mixture; B4. Place the mixture in a tube furnace to dry, introduce nitrogen gas, heat to 120°C at a heating rate of 5-8°C / min, hold for 40 minutes, heat to 250°C at a heating rate of 3-5°C / min, hold for 1 hour, heat to 400°C at a heating rate of 5-7°C / min, hold for 80 minutes, heat to 550°C at a heating rate of 8-10°C / min, hold for 90 minutes, and allow the temperature to cool naturally to below 100°C to obtain crude biochar. B5. Grind the crude biochar using a planetary ball mill, add grinding media, set the speed to 900 rpm, grind for 25 minutes, vacuum dry the ground crude biochar, set the temperature to 60℃, vacuum degree to -0.09MPa, dry for 2 hours, and pass through a 400-mesh sieve to obtain modified biochar.

[0019] Further, the mass ratio of malic acid, ε-polylysine, zinc acetate, glycerol, and deionized water is 1.25:0.625:0.469:0.469:7.8125; The mass ratio of the dried apple pomace to the modified liquid is 4:1.

[0020] Apple pomace should have a moisture content of ≤60%, a pectin content of ≥5%, and should be cored and stemmed.

[0021] Malic acid is extracted from apples, is food grade, and has a purity of ≥90%.

[0022] ε-Polylysine is food grade with a purity of ≥95%.

[0023] Zinc acetate is food grade with a particle size ≤10μm.

[0024] The glycerin is food grade with a purity of ≥99.5%.

[0025] Furthermore, the mass ratio of the medium to the crude biochar is 12:1; The medium is composed of a mixture of three types of high-purity zirconium oxide spheres: large, medium, and small. The diameter of the large high-purity zirconia spheres is 3mm, the diameter of the medium high-purity zirconia spheres is 1.5mm, and the diameter of the small high-purity zirconia spheres is 0.8mm. The mass ratio of the three types of high-purity zirconia spheres (large, medium, and small) is 1.6:1.4:1.

[0026] Secondly, the present invention provides a method for preparing a biodegradable apple packaging plastic bag, comprising the following steps: S1. Mix and stir polyethylene grafted with maleic anhydride and toughening agent at 1500 rpm for 5 minutes. Add modified corn starch and modified biochar and stir at 1800 rpm for 10 minutes. Add antifogging agent, ε-polylysine and composite additives and stir at 1500 rpm for 5 minutes to obtain material A. S2. Feed material A into a twin-screw extruder for granulation. Set the feeding section temperature to 135℃, the melting section temperature to 145℃, the mixing section temperature to 155℃, the homogenization section temperature to 160℃, the die temperature to 148℃, the screw speed to 220-250 rpm, the torque to 45-55%, the vacuum degree at the vacuum exhaust port to -0.08MPa, the cooling water temperature to 25-30℃, and the pellet length to 2-3mm to obtain masterbatch. Dry the masterbatch with hot air at a set temperature of 60℃ for 2 hours to obtain the finished masterbatch. S3. The finished masterbatch is put into a single-screw blown film machine for blown film production. After blown film production, nano-perforation and slitting are performed to make bags, resulting in biodegradable apple packaging plastic bags.

[0027] The present invention has the following beneficial effects: 1. In this invention, modified corn starch is added. It is a modified material that combines the functions of accelerating degradation, enhancing antibacterial properties, and strengthening mechanical properties. After addition, it can form a carbon source that can be utilized by microorganisms inside the film, promoting the degradation process of polyethylene grafted with maleic anhydride, polyadipate, and butylene terephthalate matrix, and shortening the degradation cycle under natural conditions. Among them, the chitosan oligosaccharide component can play a highly efficient antibacterial role, and synergistically enhance the antibacterial and freshness preservation effect of the packaging with other antibacterial components, reducing apple spoilage. Nanocellulose can construct a molecular support network to compensate for the problem of decreased film mechanical properties that may be caused by the addition of starch. At the same time, the raw material of this material is natural corn starch, which is food-grade, safe and reliable, and will not contaminate the apples.

[0028] 2. In this invention, modified biochar is added, which is the core modified material for realizing the multifunctional integration of packaging. Its raw material comes from apple processing waste, realizing the high-value recycling of agricultural waste and reducing raw material costs and environmental treatment pressure. After ternary synergistic modification, the surface of biochar forms a rich nanoporous structure and hydrophilic groups, which can not only load antibacterial components to enhance the antibacterial ability of packaging, but also promote the uniform dispersion of anti-fogging agents and enhance the anti-fogging effect. It can also adsorb ethylene gas released by apples, delay fruit ripening and senescence, and extend the shelf life. At the same time, modified biochar can improve the interfacial compatibility with polyethylene grafted maleic anhydride, polyadipate and butyl terephthalate matrix, reduce the aggregation of functional components, and ensure the stability of film mechanical properties.

[0029] 3. In this invention, composite additives are added, which are key supporting materials to ensure smooth packaging processing and stable performance. Among them, the compatibilizer can improve the interfacial bonding force between each functional component and the polyethylene grafted maleic anhydride, polyadipate and butyl terephthalate matrix, reduce component agglomeration, and ensure the uniformity of film mechanical properties and functional effects; the lubricant can improve melt flowability, avoid problems such as sticking to the mold and unstable film bubbles during processing, and improve the efficiency and quality of blow molding; the anti-hydrolysis agent can delay the hydrolytic aging of polyethylene grafted maleic anhydride during processing and use, extend the service life of the packaging, and ensure that the packaging performance does not decline during the apple's shelf life. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] It should be noted that all raw materials used in the following experiments are commercially available.

[0032] Example 1: A biodegradable apple packaging plastic bag, comprising the following raw materials: 58 parts polyethylene grafted maleic anhydride, 20 parts polyadipate, 2 parts modified corn starch, 2 parts modified biochar, 0.8 parts antifogging agent, 0.2 parts ε-polylysine and 1 part composite additive; The antifogging agent is a mixture of polyglycerol monostearate and Span 60; The mass ratio of triglyceride monostearate to Span 60 is 3:2.

[0033] The composite additive is a mixture of maleic anhydride-grafted polypropylene, calcium stearate, and triglycerides. The mass ratio of maleic anhydride-grafted polypropylene, calcium stearate, and triglycerides is 3:2:1.

[0034] The preparation of modified corn starch includes the following steps: A1. Mix chitosan oligosaccharide and deionized water, disperse using an ultrasonic disperser, set the power to 800W, disperse for 8 minutes to obtain chitosan oligosaccharide solution; A2. Mix nanocellulose and deionized water, disperse using an ultrasonic disperser, set the power to 800W, disperse for 8 minutes to obtain a cellulose solution; A3. Add corn starch to a high-speed mixer, then add chitosan oligosaccharide solution and cellulose solution in sequence and stir. Set the speed to 2000 rpm and the temperature to ≤40℃. Stir for 30 minutes to obtain a suspension. A4. Place the suspension into a spray dryer for drying, set the inlet air temperature to 160℃, the outlet air temperature to 80℃, the feed rate to 50mL / min, and the atomization pressure to 0.3MPa, to obtain modified corn starch.

[0035] The mass ratio of chitosan oligosaccharide to deionized water in A1 is 1:15; The mass ratio of nanocellulose to deionized water in A2 is 1:16.

[0036] The mass ratio of corn starch, chitosan oligosaccharide solution, and cellulose solution is 8:1:1.

[0037] The preparation of modified biochar includes the following steps: B1. Crush the apple pomace to a particle size of 5-10mm, dry it with hot air at a temperature of 60℃ for 4 hours to obtain dried apple pomace; B2. Mix malic acid, ε-polylysine, zinc acetate, glycerol and deionized water and stir at 300 rpm for 15 minutes to obtain the modified solution; B3. Mix the dried apple pomace and the modified liquid, stirring for 3-5 minutes every 30 minutes, and mix for 3 hours to obtain a mixture; B4. Place the mixture in a tube furnace to dry, introduce nitrogen gas, heat to 120°C at a heating rate of 5-8°C / min, hold for 40 minutes, heat to 250°C at a heating rate of 3-5°C / min, hold for 1 hour, heat to 400°C at a heating rate of 5-7°C / min, hold for 80 minutes, heat to 550°C at a heating rate of 8-10°C / min, hold for 90 minutes, and allow the temperature to cool naturally to below 100°C to obtain crude biochar. B5. Grind the crude biochar using a planetary ball mill, add grinding media, set the speed to 900 rpm, grind for 25 minutes, vacuum dry the ground crude biochar, set the temperature to 60℃, vacuum degree to -0.09MPa, dry for 2 hours, and pass through a 400-mesh sieve to obtain modified biochar.

[0038] The mass ratio of malic acid, ε-polylysine, zinc acetate, glycerol, and deionized water was 1.25:0.625:0.469:0.469:7.8125. The mass ratio of dried apple pomace to modified liquid is 4:1.

[0039] The mass ratio of the medium to the crude biochar was 12:1; The medium is composed of a mixture of three types of high-purity zirconia spheres: large, medium, and small. The diameter of the large high-purity zirconia spheres is 3mm, the diameter of the medium high-purity zirconia spheres is 1.5mm, and the diameter of the small high-purity zirconia spheres is 0.8mm. The mass ratio of the three types of high-purity zirconia balls (large, medium, and small) is 1.6:1.4:1.

[0040] A method for preparing a biodegradable apple packaging plastic bag includes the following steps: S1. Mix and stir polyethylene grafted with maleic anhydride and toughening agent at 1500 rpm for 5 minutes. Add modified corn starch and modified biochar and stir at 1800 rpm for 10 minutes. Add antifogging agent, ε-polylysine and composite additives and stir at 1500 rpm for 5 minutes to obtain material A. S2. Feed material A into a twin-screw extruder for granulation. Set the feeding section temperature to 135℃, the melting section temperature to 145℃, the mixing section temperature to 155℃, the homogenization section temperature to 160℃, the die temperature to 148℃, the screw speed to 220-250 rpm, the torque to 45-55%, the vacuum degree at the vacuum exhaust port to -0.08MPa, the cooling water temperature to 25-30℃, and the pellet length to 2-3mm to obtain masterbatch. Dry the masterbatch with hot air at a set temperature of 60℃ for 2 hours to obtain the finished masterbatch. S3. The finished masterbatch is put into a single-screw blown film machine for blown film production. After blown film production, nano-perforation and slitting are performed to make bags, resulting in biodegradable apple packaging plastic bags.

[0041] Example 2, a biodegradable apple packaging plastic bag, comprising the following raw materials: 61.5 parts polyethylene grafted maleic anhydride, 24 parts butylene terephthalate, 2.5 parts modified corn starch, 2.5 parts modified biochar, 1 part antifogging agent, 0.3 parts ε-polylysine and 1.25 parts composite additives; The antifogging agent is a mixture of polyglycerol monostearate and Span 60; The mass ratio of triglyceride monostearate to Span 60 is 3:2.

[0042] The toughening agent is either polyadipate or butylene terephthalate.

[0043] The composite additive is a mixture of maleic anhydride-grafted polypropylene, calcium stearate, and triglycerides. The mass ratio of maleic anhydride-grafted polypropylene, calcium stearate, and triglycerides is 3:2:1.

[0044] The preparation of modified corn starch includes the following steps: A1. Mix chitosan oligosaccharide and deionized water, disperse using an ultrasonic disperser, set the power to 800W, disperse for 8 minutes to obtain chitosan oligosaccharide solution; A2. Mix nanocellulose and deionized water, disperse using an ultrasonic disperser, set the power to 800W, disperse for 8 minutes to obtain a cellulose solution; A3. Add corn starch to a high-speed mixer, then add chitosan oligosaccharide solution and cellulose solution in sequence and stir. Set the speed to 2000 rpm and the temperature to ≤40℃. Stir for 30 minutes to obtain a suspension. A4. Place the suspension into a spray dryer for drying, set the inlet air temperature to 160℃, the outlet air temperature to 80℃, the feed rate to 50mL / min, and the atomization pressure to 0.3MPa, to obtain modified corn starch.

[0045] The mass ratio of chitosan oligosaccharide to deionized water in A1 is 1:15; The mass ratio of nanocellulose to deionized water in A2 is 1:16.

[0046] The mass ratio of corn starch, chitosan oligosaccharide solution, and cellulose solution is 8:1:1.

[0047] The preparation of modified biochar includes the following steps: B1. Crush the apple pomace to a particle size of 5-10mm, dry it with hot air at a temperature of 60℃ for 4 hours to obtain dried apple pomace; B2. Mix malic acid, ε-polylysine, zinc acetate, glycerol and deionized water and stir at 300 rpm for 15 minutes to obtain the modified solution; B3. Mix the dried apple pomace and the modified liquid, stirring for 3-5 minutes every 30 minutes, and mix for 3 hours to obtain a mixture; B4. Place the mixture in a tube furnace to dry, introduce nitrogen gas, heat to 120°C at a heating rate of 5-8°C / min, hold for 40 minutes, heat to 250°C at a heating rate of 3-5°C / min, hold for 1 hour, heat to 400°C at a heating rate of 5-7°C / min, hold for 80 minutes, heat to 550°C at a heating rate of 8-10°C / min, hold for 90 minutes, and allow the temperature to cool naturally to below 100°C to obtain crude biochar. B5. Grind the crude biochar using a planetary ball mill, add grinding media, set the speed to 900 rpm, grind for 25 minutes, vacuum dry the ground crude biochar, set the temperature to 60℃, vacuum degree to -0.09MPa, dry for 2 hours, and pass through a 400-mesh sieve to obtain modified biochar.

[0048] The mass ratio of malic acid, ε-polylysine, zinc acetate, glycerol, and deionized water was 1.25:0.625:0.469:0.469:7.8125. The mass ratio of dried apple pomace to modified liquid is 4:1.

[0049] The mass ratio of the medium to the crude biochar was 12:1; The medium is composed of a mixture of three types of high-purity zirconia spheres: large, medium, and small. The diameter of the large high-purity zirconia spheres is 3mm, the diameter of the medium high-purity zirconia spheres is 1.5mm, and the diameter of the small high-purity zirconia spheres is 0.8mm. The mass ratio of the three types of high-purity zirconia balls (large, medium, and small) is 1.6:1.4:1.

[0050] A method for preparing a biodegradable apple packaging plastic bag includes the following steps: S1. Mix and stir polyethylene grafted with maleic anhydride and toughening agent at 1500 rpm for 5 minutes. Add modified corn starch and modified biochar and stir at 1800 rpm for 10 minutes. Add antifogging agent, ε-polylysine and composite additives and stir at 1500 rpm for 5 minutes to obtain material A. S2. Feed material A into a twin-screw extruder for granulation. Set the feeding section temperature to 135℃, the melting section temperature to 145℃, the mixing section temperature to 155℃, the homogenization section temperature to 160℃, the die temperature to 148℃, the screw speed to 220-250 rpm, the torque to 45-55%, the vacuum degree at the vacuum exhaust port to -0.08MPa, the cooling water temperature to 25-30℃, and the pellet length to 2-3mm to obtain masterbatch. Dry the masterbatch with hot air at a set temperature of 60℃ for 2 hours to obtain the finished masterbatch. S3. The finished masterbatch is put into a single-screw blown film machine for blown film production. After blown film production, nano-perforation and slitting are performed to make bags, resulting in biodegradable apple packaging plastic bags.

[0051] Example 3: A biodegradable apple packaging plastic bag, comprising the following raw materials: 65 parts polyethylene grafted maleic anhydride, 28 parts butylene terephthalate, 3 parts modified corn starch, 3 parts modified biochar, 1.2 parts antifogging agent, 0.4 parts ε-polylysine, and 1.5 parts composite additives. The antifogging agent is a mixture of polyglycerol monostearate and Span 60; The mass ratio of triglyceride monostearate to Span 60 is 3:2.

[0052] The composite additive is a mixture of maleic anhydride-grafted polypropylene, calcium stearate, and triglycerides. The mass ratio of maleic anhydride-grafted polypropylene, calcium stearate, and triglycerides is 3:2:1.

[0053] The preparation of modified corn starch includes the following steps: A1. Mix chitosan oligosaccharide and deionized water, disperse using an ultrasonic disperser, set the power to 800W, disperse for 8 minutes to obtain chitosan oligosaccharide solution; A2. Mix nanocellulose and deionized water, disperse using an ultrasonic disperser, set the power to 800W, disperse for 8 minutes to obtain a cellulose solution; A3. Add corn starch to a high-speed mixer, then add chitosan oligosaccharide solution and cellulose solution in sequence and stir. Set the speed to 2000 rpm and the temperature to ≤40℃. Stir for 30 minutes to obtain a suspension. A4. Place the suspension into a spray dryer for drying, set the inlet air temperature to 160℃, the outlet air temperature to 80℃, the feed rate to 50mL / min, and the atomization pressure to 0.3MPa, to obtain modified corn starch.

[0054] The mass ratio of chitosan oligosaccharide to deionized water in A1 is 1:15; The mass ratio of nanocellulose to deionized water in A2 is 1:16.

[0055] The mass ratio of corn starch, chitosan oligosaccharide solution, and cellulose solution is 8:1:1.

[0056] The preparation of modified biochar includes the following steps: B1. Crush the apple pomace to a particle size of 5-10mm, dry it with hot air at a temperature of 60℃ for 4 hours to obtain dried apple pomace; B2. Mix malic acid, ε-polylysine, zinc acetate, glycerol and deionized water and stir at 300 rpm for 15 minutes to obtain the modified solution; B3. Mix the dried apple pomace and the modified liquid, stirring for 3-5 minutes every 30 minutes, and mix for 3 hours to obtain a mixture; B4. Place the mixture in a tube furnace to dry, introduce nitrogen gas, heat to 120°C at a heating rate of 5-8°C / min, hold for 40 minutes, heat to 250°C at a heating rate of 3-5°C / min, hold for 1 hour, heat to 400°C at a heating rate of 5-7°C / min, hold for 80 minutes, heat to 550°C at a heating rate of 8-10°C / min, hold for 90 minutes, and allow the temperature to cool naturally to below 100°C to obtain crude biochar. B5. Grind the crude biochar using a planetary ball mill, add grinding media, set the speed to 900 rpm, grind for 25 minutes, vacuum dry the ground crude biochar, set the temperature to 60℃, vacuum degree to -0.09MPa, dry for 2 hours, and pass through a 400-mesh sieve to obtain modified biochar.

[0057] The mass ratio of malic acid, ε-polylysine, zinc acetate, glycerol, and deionized water was 1.25:0.625:0.469:0.469:7.8125. The mass ratio of dried apple pomace to modified liquid is 4:1.

[0058] The mass ratio of the medium to the crude biochar was 12:1; The medium is composed of a mixture of three types of high-purity zirconia spheres: large, medium, and small. The diameter of the large high-purity zirconia spheres is 3mm, the diameter of the medium high-purity zirconia spheres is 1.5mm, and the diameter of the small high-purity zirconia spheres is 0.8mm. The mass ratio of the three types of high-purity zirconia balls (large, medium, and small) is 1.6:1.4:1.

[0059] A method for preparing a biodegradable apple packaging plastic bag includes the following steps: S1. Mix and stir polyethylene grafted with maleic anhydride and toughening agent at 1500 rpm for 5 minutes. Add modified corn starch and modified biochar and stir at 1800 rpm for 10 minutes. Add antifogging agent, ε-polylysine and composite additives and stir at 1500 rpm for 5 minutes to obtain material A. S2. Feed material A into a twin-screw extruder for granulation. Set the feeding section temperature to 135℃, the melting section temperature to 145℃, the mixing section temperature to 155℃, the homogenization section temperature to 160℃, the die temperature to 148℃, the screw speed to 220-250 rpm, the torque to 45-55%, the vacuum degree at the vacuum exhaust port to -0.08MPa, the cooling water temperature to 25-30℃, and the pellet length to 2-3mm to obtain masterbatch. Dry the masterbatch with hot air at a set temperature of 60℃ for 2 hours to obtain the finished masterbatch. S3. The finished masterbatch is put into a single-screw blown film machine for blown film production. After blown film production, nano-perforation and slitting are performed to make bags, resulting in biodegradable apple packaging plastic bags.

[0060] Comparative Example 1: The difference between this comparative example and Example 1 is that: Unmodified biochar was used in this comparative example.

[0061] Comparative Example 2: The difference between this comparative example and Example 1 is that: ε-polylysine was not used in this comparative example.

[0062] Comparative Example 3 differs from Example 1 in that: Modified starch was not used in this comparative example.

[0063] Performance testing: The biodegradable apple packaging plastic bags prepared in Examples 1, 2, 3, Comparative Examples 1, 2, and 3 were tested.

[0064] Performance testing: The relevant properties of the biodegradable apple packaging plastic bags and their preparation methods provided in Examples 1-3 and Comparative Examples 1-3 were tested respectively, and the test data are recorded in Table 1 below:

[0065] Based on the above data, the following conclusions can be drawn: The apple rot rate of Examples 1-3 after 30 days of storage at room temperature was much better than that of Comparative Examples 1-3. The key point is that the examples added modified biochar. The porous structure of the modified biochar adsorbs the ethylene released by the apples, thus delaying ripening and senescence.

[0066] (2) The antibacterial rate of Escherichia coli in Examples 1-3 is far superior to that in Comparative Examples 1-3. The key point is that the examples added ε-polylysine, which has a significant inhibitory effect on microorganisms such as Escherichia coli that cause apple mold, and can effectively reduce the rate of apple decay during storage.

[0067] (3) The particle size of the film disintegrating within 7 days under the industrial composting conditions of Examples 1-3 is much better than that of Comparative Examples 1-3. The key point is that modified starch was added to the examples. The enzymatic hydrolysis porous structure of the modified starch accelerates the penetration of water and microorganisms, which promotes the rapid disintegration of the film.

[0068] Through the above demonstrations, the present invention is significantly superior to the control group in terms of apple rot rate after 30 days of storage at room temperature, antibacterial rate against Escherichia coli, and particle size of film disintegration within 7 days under industrial composting conditions, thus verifying the advanced nature and rationality of the preparation process.

[0069] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0070] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A biodegradable apple packaging plastic bag, characterized in that, The biodegradable apple packaging plastic bag comprises the following raw materials: 58-65 parts polyethylene grafted maleic anhydride, 20-28 parts toughening agent, 2-3 parts modified corn starch, 2-3 parts modified biochar, 0.8-1.2 parts anti-fogging agent, 0.2-0.4 parts ε-polylysine and 1-1.5 parts composite additives; The antifogging agent is a mixture of triglyceride monostearate and Span 60; The mass ratio of the triglyceride monostearate to Span 60 is 3:

2.

2. The biodegradable apple packaging plastic bag according to claim 1, characterized in that, The toughening agent is either polyadipate or butylene terephthalate.

3. The biodegradable apple packaging plastic bag according to claim 1, characterized in that, The composite additive is a mixture of maleic anhydride-grafted polypropylene, calcium stearate and triglycerides. The mass ratio of maleic anhydride-grafted polypropylene, calcium stearate, and triglycerides is 3:2:

1.

4. The biodegradable apple packaging plastic bag according to claim 1, characterized in that, The preparation of the modified corn starch includes the following steps: A1. Mix chitosan oligosaccharide and deionized water, and disperse using an ultrasonic disperser to obtain a chitosan oligosaccharide solution; A2. Mix nanocellulose and deionized water, and disperse using an ultrasonic disperser to obtain a cellulose solution; A3. Add corn starch to a high-speed mixer, then add chitosan oligosaccharide solution and cellulose solution in sequence and stir to obtain a suspension; A4. The suspension is dried in a spray dryer to obtain modified corn starch.

5. The biodegradable apple packaging plastic bag according to claim 4, characterized in that, The mass ratio of chitosan oligosaccharide to deionized water in A1 is 1:15; The mass ratio of nanocellulose to deionized water in A2 is 1:

16.

6. The biodegradable apple packaging plastic bag according to claim 4, characterized in that, The mass ratio of the corn starch, chitosan oligosaccharide solution, and cellulose solution is 8:1:

1.

7. The biodegradable apple packaging plastic bag according to claim 1, characterized in that, The preparation of the modified biochar includes the following steps: B1. Crush the apple pomace and dry it with hot air to obtain dried apple pomace; B2. Malic acid, ε-polylysine, zinc acetate, glycerol, and deionized water are mixed and stirred to obtain a modified solution; B3. Mix the dried apple pomace and the modified liquid to obtain a mixture; B4. The mixture is placed in a tube furnace for drying, and nitrogen gas is introduced to obtain crude biochar; B5. The crude biochar was ground using a planetary ball mill with grinding media added. The ground crude biochar was then vacuum dried to obtain modified biochar.

8. The biodegradable apple packaging plastic bag according to claim 7, characterized in that, The mass ratio of malic acid, ε-polylysine, zinc acetate, glycerol, and deionized water is 1.25:0.625:0.469:0.469:7.8125. The mass ratio of the dried apple pomace to the modified liquid is 4:

1.

9. The biodegradable apple packaging plastic bag according to claim 7, characterized in that, The mass ratio of the medium to the crude biochar is 12:1; The medium is composed of a mixture of three types of high-purity zirconium oxide spheres: large, medium, and small. The mass ratio of the three types of high-purity zirconia spheres (large, medium, and small) is 1.6:1.4:

1.

10. A method for preparing a biodegradable apple packaging plastic bag according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Mix and stir polyethylene grafted with maleic anhydride and toughening agent, add modified corn starch and modified biochar and stir, add antifogging agent, ε-polylysine and composite additives and stir to obtain material A; S2. Feed material A into a twin-screw extruder for granulation to obtain masterbatch. Dry the masterbatch with hot air to obtain the finished masterbatch. S3. The finished masterbatch is put into a single-screw blown film machine for blown film production. After blown film production, nano-perforation and slitting are performed to make bags, resulting in biodegradable apple packaging plastic bags.

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