Degradable express bag material and preparation method thereof

Abstract

The invention discloses a degradable express bag material and a preparation method thereof, and relates to the technical field of high polymer materials. The invention discloses a degradable express bag material. The composite material is prepared from the following raw materials in parts by weight: 40 to 50 parts of poly (butylene adipate-co-terephthalate), 20 to 30 parts of polycaprolactone, 5 to 8 parts of modified bamboo fiber, 2 to 4 parts of modified nano montmorillonite, 3 to 6 parts of tributyl citrate, 0.1 to 0.3 part of antioxidant 1076, 1 to 2 parts of iron dithiocarbamate master batch, 2 to 3 parts of maleic anhydride grafted poly (butylene adipate-co-terephthalate) and 0.3 to 0.6 part of zinc stearate. 0.1 to 0.3 part of baicalein; and 1 to 3 parts of chitosan-sorbitol composite coating liquid. According to the degradable express bag material, poly (butylene adipate-co-terephthalate) and polycaprolactone are used as main degradable raw materials, modified bamboo fibers and modified nano-montmorillonite are matched to enhance the mechanical property, an antioxidant 1076, baicalein and the like are added to guarantee the stability and functionality, temperature is accurately controlled in the preparation process, multi-step modification is adopted for optimizing component combination, and the degradable express bag material is prepared. The performance is improved through the composite coating, degradability is achieved, and good usability is achieved.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a biodegradable express delivery bag material and its preparation method. Background Technology

[0002] With the booming development of the e-commerce industry, the volume of express delivery business has exploded, and the demand for express packaging materials has also surged. Currently, most express bags on the market are made of traditional non-degradable plastics such as polyethylene (PE). These materials have a degradation cycle of decades or even hundreds of years in the natural environment. After large-scale use, they are prone to forming "white pollution," which not only occupies land resources and damages soil structure, but also pollutes water bodies and the ecological environment through rainwater erosion and microbial decomposition, posing a potential threat to the survival of animals and plants and human health.

[0003] To address the problem of plastic pollution, countries have successively introduced policies such as "plastic restriction orders" and "plastic bans" to promote the research and application of biodegradable packaging materials. Currently, most biodegradable express delivery bag materials use biodegradable resins such as polybutylene terephthalate (PBAT) and polycaprolactone (PCL) as the base material. However, single base materials have obvious defects: PBAT has good toughness but insufficient rigidity, and is prone to aging and damage after long-term use; PCL has a fast degradation rate but low mechanical strength, making it difficult to meet the load-bearing and puncture resistance requirements of express delivery bags.

[0004] To improve performance, some solutions add natural fibers or nanofillers. However, unmodified natural fibers have poor compatibility with resins and are prone to agglomeration, leading to uneven mechanical properties. Ordinary nano-montmorillonite has insufficient dispersibility and cannot fully exert its reinforcing effect. In addition, existing materials also suffer from weak antioxidant properties, poor thermal stability, and insufficient barrier properties. Furthermore, some preparation processes are complex and costly, making it difficult to achieve large-scale mass production and failing to fully meet the express delivery industry's demand for packaging materials that are "low-cost, cost-effective, and highly practical." Therefore, developing a biodegradable express bag material that combines excellent degradation performance, mechanical properties, stability, and a simple preparation process has become a key issue that the industry urgently needs to address. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a biodegradable express delivery bag material and its preparation method, solving the problems of insufficient performance, inefficient degradation, and white pollution caused by traditional express delivery bag materials.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A biodegradable express delivery bag material comprises the following raw materials in parts by weight: 40-50 parts polybutylene adipate terephthalate, 20-30 parts polycaprolactone, 5-8 parts modified bamboo fiber, 2-4 parts modified nano-montmorillonite, 3-6 parts tributyl citrate, 0.1-0.3 parts antioxidant 1076, 1-2 parts ferric dithiocarbamate masterbatch, 2-3 parts maleic anhydride-grafted polybutylene adipate terephthalate, 0.3-0.6 parts zinc stearate, 0.1-0.3 parts baicalin, and 1-3 parts chitosan-sorbitol composite coating liquid.

[0007] Furthermore, the carrier of the iron dithiocarbamate masterbatch is polybutylene adipate terephthalate, which ensures the compatibility of iron dithiocarbamate with the substrate. The mass fraction of iron dithiocarbamate is 28-32%, which avoids performance fluctuations caused by excessively high local concentrations. The particle size of the masterbatch is 2-4mm, which is suitable for feeding into a twin-screw extruder and prevents material blockage. The total solids content of the chitosan-sorbitol composite coating liquid is 1wt%, which avoids film embrittlement caused by excessive coating thickness. The mass ratio of chitosan to sorbitol is 3:2, which can balance the barrier properties of chitosan and the flexibility of sorbitol, thereby improving the water-proof and damage-proof capabilities of the express bag.

[0008] Furthermore, the baicalin is a spray-dried powder with a particle size D50≤5μm, which can increase the specific surface area of ​​baicalin, allowing it to be uniformly dispersed in the substrate and fully exert its anti-ultraviolet aging effect. After surface coating treatment with 0.5wt% chitosan aqueous solution, the coating layer thickness is 50-100nm, which can inhibit the aggregation of baicalin, reduce the loss of active ingredients during processing, and extend the performance stability period of the material under light environment.

[0009] Furthermore, the modified bamboo fiber is prepared using the following specific steps: A1. Take dried bamboo fiber, add phosphate buffer solution (pH=5.0), stir to disperse, then add cellulase. React at 50-55℃ and 150r / min for 4-5 hours to degrade cellulose on the surface of bamboo fiber, forming a porous structure and increasing the adsorption capacity of subsequent modifiers. After the reaction, filter and rinse three times with 40℃ deionized water until the conductivity of the eluent is ≤200μS / cm to remove residual enzyme solution and impurities, avoiding interference with subsequent reactions. Then, transfer the fiber to a 0.5% sodium bicarbonate solution, heat to 50℃ and soak until the pH of the fiber reaches the specified value. A pH of 7.0-7.5 neutralizes the acidity of the fiber, providing a neutral environment for β-cyclodextrin modification. After filtration, the fiber is added to a 5% (w / w) β-cyclodextrin aqueous solution and stirred at 60°C and 200 rpm for 2 minutes. Then, hexadecyltrimethylammonium bromide is added in two portions, and stirring is continued for 2 hours to adjust the hydrophilicity and hydrophobicity of the fiber and reduce interfacial repulsion with PBAT / PCL. Subsequently, disodium ethylenediaminetetraacetate is added and stirred for another hour to chelate metallic impurities and prevent them from reducing the material's antioxidant stability. After the reaction is complete, the fiber is filtered and vacuum dried at 80°C for 6 hours to obtain the first modified bamboo fiber. A2. The first modified bamboo fiber was added to anhydrous ethanol and ultrasonically dispersed for 30 min. Then, silane coupling agent KH-550 was added and refluxed at 70-75℃ for 3 h. This can introduce organic functional groups on the fiber surface, build chemical connections between the fiber and the organic substrate, and reduce agglomeration. After filtration, the fiber was transferred to a 10% (w / w) vanillin ethanol solution, and triethylamine was added. The mixture was stirred at 50-55℃ and 200 r / min for 2 h to further modify the fiber surface, enhance the interfacial bonding with PBAT / PCL, and improve the synergistic mechanical properties. After the reaction, the fiber was washed three times with ethanol to ensure the purity of the modified fiber. The fiber was then vacuum dried at 60℃ for 5 h to obtain the second modified bamboo fiber. A3. Take the second modified bamboo fiber and add it to deionized water. Stir at 300 r / min to make a suspension. Add zinc nitrate, dissolve by ultrasonication, and then add dropwise a 1.0 mol / L 2-methylimidazolium ethanol solution. Stir at 30-35℃ and 300 r / min for 4 hours to generate metal-organic framework (MOF) structures on the fiber surface, which simultaneously improves the mechanical support and biodegradation rate of the fiber. After the reaction is completed, filter the product and vacuum dry it at 70℃ for 8 hours to avoid the generation of bubbles in subsequent processing, thus obtaining modified bamboo fiber.

[0010] Furthermore, the ratio of dried bamboo fiber, phosphate buffer, cellulase, sodium bicarbonate solution, β-cyclodextrin aqueous solution, hexadecyltrimethylammonium bromide, and disodium EDTA in A1 is 100g:300-350mL:5-10g:400-500g:200-250mL:1-2g:0.5-1.0g; wherein the cellulase activity is 1000U / g.

[0011] Furthermore, the ratio of the first modified bamboo fiber, anhydrous ethanol, silane coupling agent KH-550, vanillin ethanol solution, and triethylamine in A2 is 100g: 200-250mL: 4-6g: 30-50mL: 1-2mL.

[0012] Furthermore, the ratio of the amount of the second modified bamboo fiber, deionized water, zinc nitrate, and 2-methylimidazole ethanol solution in A3 is 100g: 300-350mL: 8-10g: 220-280mL.

[0013] Furthermore, the modified nano-montmorillonite is prepared using the following specific steps: B1. Add nano-montmorillonite to deionized water and stir at 500 rpm for 30 min to disperse evenly, ensuring uniform dispersion and preventing aggregation. Then add Tris-HCl buffer solution (pH 8.5) and sonicate for 1 h until the suspension is stable. Add dopamine hydrochloride and stir at 200 rpm for 6 h at 25-30℃ to form a polydopamine coating, enhancing the reactivity and dispersibility of montmorillonite. Next, add 0.05 mol / L silver nitrate solution and stir in the dark for 2 h. Then add sodium ascorbate and continue stirring in the dark for 1 h to generate silver nanoparticles, giving montmorillonite basic antibacterial function. Finally, centrifuge and wash the precipitate twice with deionized water, then vacuum dry at 50-60℃ for 6 h to obtain the first modified nano-montmorillonite. B2. Take the first modified nano-montmorillonite and add anhydrous ethanol. After ultrasonic dispersion for 30 min, add polyethylene glycol 600 and reflux at 200 r / min at 60-70℃ for 3 h to reduce the surface energy of montmorillonite and further improve its compatibility with PBAT / PCL, avoiding agglomeration during processing. After the reaction is completed, centrifuge and separate the precipitate. Wash the precipitate twice with anhydrous ethanol and vacuum dry at 60℃ for 5 h to obtain the second modified nano-montmorillonite. B3. Take the second modified nano-montmorillonite and add it to deionized water. Disperse it ultrasonically for 30 minutes until there is no sedimentation in the suspension. Add vanillin and melamine, stir until completely dissolved, and then heat to 80℃ and stir at 200r / min for 6 hours to form a cross-linked structure on the surface of montmorillonite, which enhances its interfacial bonding with the substrate and improves the rigidity and puncture resistance of the material. After the reaction is completed, centrifuge and separate the precipitate. Wash the precipitate twice with deionized water and vacuum dry at 80℃ for 8 hours to obtain modified nano-montmorillonite.

[0014] Furthermore, the ratio of nano-montmorillonite, deionized water, tris(hydroxymethyl)aminomethane-hydrochloric acid buffer, dopamine hydrochloride, silver nitrate solution, and sodium ascorbate in B1 is 100g: 400-450mL: 400-450mL: 5-7g: 30-40mL: 0.3-0.5g.

[0015] Furthermore, the ratio of the first modified nano-montmorillonite, anhydrous ethanol, and polyethylene glycol 600 in B2 is 100g: 300-350mL: 5-8g.

[0016] Furthermore, the ratio of the second modified nano-montmorillonite, deionized water, vanillin, and melamine in B3 is 100g:300-350mL:5-7g:3-4g.

[0017] A method for preparing a biodegradable express delivery bag material specifically includes the following steps: S1. Place polybutylene adipate terephthalate and polycaprolactone granules into a vacuum drying oven and dry at 85-90℃ for 5-6 hours. Place modified bamboo fiber and modified nano-montmorillonite into another vacuum drying oven and dry at 75-80℃ for 4 hours to completely remove moisture from the raw materials, avoid air bubbles during twin-screw extrusion, and ensure material density. Take 0.1-0.3 parts of antioxidant 1076, 0.3-0.6 parts of zinc stearate, and 0.1-0.3 parts of baicalin and mix them in a high-speed mixer at 50-60℃ and 1500-2000r / min for 5-8 minutes. Then add 1.0-2.0 parts of ferric dithiocarbamate masterbatch and continue mixing for 3-5 minutes to prepare a uniform functional additive premix. S2. Start the twin-screw extruder and set the temperature parameters for each section: Zone 1 130-140℃, Zone 2 145-155℃, Zone 3 155-165℃, Zone 4 160-170℃, and Die head 150-160℃. Gradual heating helps melt the raw material and prevents localized overheating that could lead to PBAT / PCL degradation. Once the temperatures in each section have stabilized, adjust the screw speed to 200-250 r / min. Continuously add 40-50 parts of polybutylene terephthalate (PET) and 20-30 parts of polycaprolactone (PVC) through the main feed port. At the side feed port located one-third of the way from the die head, add 5-8 parts of modified bamboo fiber and 2-4 parts of PVC. Modified nano-montmorillonite is added to prevent premature thermal degradation of the fiber / montmorillonite. At the feed port on the other side, 2 / 3 of the way from the die head, add 3-6 parts of tributyl citrate, 2-3 parts of maleic anhydride-grafted polybutylene adipate terephthalate, and the premixed functional additives prepared by S1. Adding these later reduces volatilization. After the material is melted, sheared, and thoroughly mixed by the extruder, it is extruded from the die head to form strips. The strips are then cooled in a 25-30℃ cold water bath, and then dried by an air-drying device with a temperature set at 25-35℃ and a speed controlled at 3-5 m / s. Finally, the strips are cut into 3-4 mm long particles by a pelletizer to obtain composite masterbatch. S3. Start the blown film machine and set the temperatures for each section: Zone 1 of the barrel 140-150℃, Zone 2 of the barrel 150-160℃, Zone 3 of the barrel 160-170℃, and the die head 155-165℃, to ensure that the composite masterbatch is fully melted and does not degrade. After the temperature stabilizes, adjust the screw speed to 90-110 r / min. Add the composite masterbatch to the blown film machine hopper. After the masterbatch melts in the barrel, it is extruded from the T-die head to form a sheet material with a thickness of 1.0-1.2 mm. The sheet material is first preheated by a preheating roller at 70-75℃ before entering the drawing process. Stretching device: Longitudinal stretching is performed by a 2.5 times speed difference between stretching rollers, with the stretching temperature controlled at 70-75℃. After a 2-3 second buffer period following the end of longitudinal stretching, transverse stretching is performed at 80-85℃ at 3 times the speed difference. This causes the molecules to align, significantly improving the tensile strength and elongation at break of the film. The stretched film is then sent to a heat-setting device at 90-95℃ for setting, eliminating tensile stress and ensuring dimensional stability. After cooling by cooling rollers at 30-35℃, the film is finally wound up by a winding device to obtain a film with a thickness of 40-60μm. S4. Spray 1-3 parts of chitosan-sorbitol composite coating liquid evenly onto the film surface using a spraying device. The coating thickness is 5-8μm, which can improve the surface barrier properties of the film. After spraying, put the bag into an 80℃ drying device and dry for 25-30 seconds to ensure that the coating adheres tightly and avoid drying for too long, which will cause the film to become brittle. Finally, a biodegradable express bag material is obtained.

[0018] Furthermore, in S3, the longitudinal stretching rate gradient is 5-8 mm / s, and the transverse stretching rate gradient is 8-12 mm / s. The stretching rate can be precisely controlled according to the difference in mechanical requirements between the longitudinal and transverse directions of the film, avoiding local stress concentration that could lead to film breakage. The tension control in the heat setting device is 0.5-0.8 MPa, which eliminates internal stress while ensuring the stability of the film shape and preventing shrinkage or wrinkling after heat setting. The synergistic effect of these three elements ensures that the stretched film has uniform mechanical properties and stable dimensions, meeting the mechanical and dimensional stability requirements of express bags during sorting and transportation.

[0019] This invention provides a biodegradable express delivery bag material and its preparation method, which has the following beneficial effects: 1. This biodegradable express delivery bag material uses polybutylene adipate terephthalate (PEPA) and polycaprolactone (PVC) as its core base materials. Both PEPA and PVC possess mature biodegradability. Combined with modified bamboo fiber, chitosan-sorbitol composite coating, and other biodegradable components, a complete degradation system is constructed. In natural environments such as soil and water, the material can be gradually decomposed by microorganisms into harmless small molecules such as carbon dioxide and water, leaving no significant toxic residue. Its degradation cycle is highly compatible with the short-term use and rapid replacement characteristics of express delivery packaging, complying with the plastic restriction and ban policies of various countries, and directly replacing traditional polyethylene express delivery bags. This reduces white pollution in the express delivery industry at the source and contributes to the green transformation of the packaging sector.

[0020] 2. Addressing the shortcomings of traditional biodegradable materials, such as insufficient toughness leading to breakage and inadequate rigidity for load-bearing capacity, this invention achieves synergistic optimization through modified bamboo fiber and modified nano-montmorillonite. Modified bamboo fiber, after multiple treatments, exhibits improved compatibility with the substrate, enhancing the material's tensile and puncture resistance. The uniformly dispersed modified nano-montmorillonite strengthens rigidity and impact resistance. Combined with the inherent toughness of PBAT and PCL, a mechanical structure that balances rigidity and flexibility is formed. Simultaneously, the melt shearing of twin-screw extrusion ensures thorough mixing of components, while the longitudinal and transverse stretching during blown film extrusion results in a more regular molecular arrangement. This makes the material less prone to tearing or damage during sorting, transportation, and delivery, even when bearing heavy loads or coming into contact with sharp objects.

[0021] 3. The material incorporates antioxidant 1076 and chitosan-coated baicalein, forming a synergistic stabilizing system. Antioxidant 1076 inhibits thermo-oxidative free radical reactions during processing and use, delaying molecular chain breakage. The coated baicalein is more evenly dispersed, enhancing its resistance to UV aging and reducing the damage to performance caused by light. Furthermore, the vacuum drying temperature control and precise temperature adjustment at each stage of extrusion during the preparation process, combined with zinc stearate and maleic anhydride grafted PBAT to optimize processing stability, allow the material to form a stable polymer network that can withstand the effects of temperature and humidity fluctuations. Under normal temperature storage, its performance stability exceeds 6 months. Even during short-term transportation in extreme summer and winter environments, it will not experience discoloration or brittleness, reducing additional costs for express delivery companies due to premature packaging aging.

[0022] 4. The core processes of this invention are all conventional and mature technologies in the packaging industry, requiring no special equipment. Enterprises only need to adjust the parameters of their existing production lines to achieve mass production, significantly reducing modification costs and technical barriers. The final material thickness is controlled at 40-60μm, comparable to traditional express delivery bags, balancing thinness and barrier properties, and can package various items such as clothing and electronic products. Simultaneously, the material has good processing fluidity, making it less prone to clogging or breakage during production, achieving efficiency on par with traditional express delivery bags, thus balancing performance and mass production efficiency, facilitating widespread adoption. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Example 1: Preparation of biodegradable express delivery bag material. The specific preparation steps are as follows: S1. Place polybutylene adipate terephthalate and polycaprolactone granules into a vacuum drying oven and dry at 85℃ for 5 hours. Place bamboo fiber and nano-montmorillonite into another vacuum drying oven and dry at 75℃ for 4 hours. Take 0.1 parts of antioxidant 1076, 0.3 parts of zinc stearate, and 0.1 parts of baicalin and mix them in a high-speed mixer at 50℃ and 1500r / min for 5 minutes. Then add 1.0 part of ferric dithiocarbamate masterbatch and continue mixing for 3 minutes to prepare a uniform functional additive premix. S2. Start the twin-screw extruder and set the temperature parameters for each section: Zone 1 130℃, Zone 2 145℃, Zone 3 155℃, Zone 4 160℃, and Die head 150℃. After the temperature of each section stabilizes, adjust the screw speed to 200 r / min. Continuously add 40 parts of polybutylene adipate terephthalate and 20 parts of polycaprolactone through the main feed port. Add 5 parts of bamboo fiber and 2 parts of nano-montmorillonite through the side feed port at 1 / 3 of the distance from the die head. Add 2 parts of bamboo fiber and 2 parts of nano-montmorillonite through the side feed port at 2 / 3 of the distance from the die head. On the other side of the feed port, add 3 parts of tributyl citrate, 2 parts of maleic anhydride-grafted polybutylene adipate terephthalate and the functional additive premix prepared by S1; after the material is melted and sheared by the extruder and fully mixed, it is extruded from the die head to form strips; the strips are sent to a 25°C cold water bath for cooling, and then the surface moisture is dried by an air drying device with the air temperature set at 25°C and the air speed controlled at 3m / s. Finally, it is cut into 3mm long particles by a pelletizer to obtain composite masterbatch; S3. Start the blown film machine and set the temperatures for each section: 140℃ for zone 1 of the barrel, 150℃ for zone 2 of the barrel, 160℃ for zone 3 of the barrel, and 155℃ for the die head. After the temperature stabilizes, adjust the screw speed to 90 r / min. Add the composite masterbatch to the blown film machine hopper. After the masterbatch melts in the barrel, it is extruded from the T-die head to form a 1.0 mm thick sheet. The sheet is preheated by a 70℃ preheating roller and then enters the stretching device. It is stretched longitudinally by a 2.5 times speed difference between the stretching rollers, with a rate gradient of 5 mm / s and a stretching temperature controlled at 70℃. After a 2-second buffer after the longitudinal stretching, it is stretched laterally by 3 times the speed at 80℃, with a rate gradient of 8 mm / s. The stretched film is then sent to a 90℃ heat setting device for setting, with a tension controlled at 0.5 MPa. It is then cooled by a 30℃ cooling roller and finally wound up by a winding device to obtain a film with a thickness of 40 μm. S4. One part of chitosan-sorbitol composite coating liquid is evenly sprayed onto the film surface using a spraying device, with a coating thickness of 5μm. The sprayed bag is then placed in an 80℃ drying device and dried for 25s to obtain the biodegradable express bag material.

[0025] Example 2: Preparation of biodegradable express delivery bag material. The specific preparation steps are as follows: S1. Place polybutylene adipate terephthalate and polycaprolactone granules into a vacuum drying oven and dry at 90℃ for 6 hours; place bamboo fiber and nano-montmorillonite into another vacuum drying oven and dry at 80℃ for 4 hours; take 0.3 parts of antioxidant 1076, 0.6 parts of zinc stearate, and 0.3 parts of baicalin and mix them in a high-speed mixer at 60℃ and 2000r / min for 8 minutes; then add 2.0 parts of ferric dithiocarbamate masterbatch and continue mixing for 5 minutes to prepare a uniform functional additive premix. S2. Start the twin-screw extruder and set the temperature parameters for each section: Zone 1 140℃, Zone 2 155℃, Zone 3 165℃, Zone 4 170℃, and Die Head 160℃. After the temperature of each section stabilizes, adjust the screw speed to 250 r / min. Continuously add 50 parts of polybutylene adipate terephthalate and 30 parts of polycaprolactone through the main feed port. Add 8 parts of bamboo fiber and 4 parts of nano-montmorillonite through the side feed port at 1 / 3 of the distance from the die head. Add 2 / 3 of the distance from the die head... On the other side of the feed port, add 6 parts of tributyl citrate, 3 parts of maleic anhydride-grafted polybutylene adipate terephthalate and S1 prepared functional additive premix; after the material is melted and sheared by the extruder and fully mixed, it is extruded from the die head to form strip material; the strip material is sent into a 30°C cold water bath for cooling, and then the surface moisture is dried by the air drying device, with the air temperature set at 35°C and the air speed controlled at 5m / s. Finally, it is cut into 4mm long particles by the pelletizer to obtain composite masterbatch; S3. Start the blown film machine and set the temperatures for each section: 150℃ for zone 1 of the barrel, 160℃ for zone 2 of the barrel, 170℃ for zone 3 of the barrel, and 165℃ for the die head. After the temperature stabilizes, adjust the screw speed to 110 r / min. Add the composite masterbatch to the blown film machine hopper. After the masterbatch melts in the barrel, it is extruded from the T-die head to form a 1.2 mm thick sheet. The sheet is preheated by a 75℃ preheating roller and then enters the stretching device. It is stretched longitudinally by a 2.5 times speed difference between the stretching rollers, with a rate gradient of 8 mm / s and a stretching temperature controlled at 75℃. After a 3-second buffer after the longitudinal stretching, it is stretched laterally by 3 times the speed at 85℃, with a rate gradient of 12 mm / s. The stretched film is then sent to a 95℃ heat setting device for setting, with a tension controlled at 0.8 MPa. It is then cooled by a 35℃ cooling roller and finally wound up by a winding device to obtain a 60 μm thick film. S4. Three parts of chitosan-sorbitol composite coating liquid were evenly sprayed onto the film surface using a spraying device, with a coating thickness of 8μm. The sprayed bag was then placed in an 80℃ drying device and dried for 30s to obtain the biodegradable express bag material.

[0026] Example 3: Preparation of biodegradable express delivery bag material. The specific preparation steps are as follows: S1. Place polybutylene adipate terephthalate and polycaprolactone granules into a vacuum drying oven and dry at 88℃ for 5.5h. Place bamboo fiber and nano-montmorillonite into another vacuum drying oven and dry at 77℃ for 4h. Take 0.2 parts of antioxidant 1076, 0.4 parts of zinc stearate, and 0.2 parts of baicalin and mix them in a high-speed mixer at 55℃ and 1750r / min for 7min. Then add 1.5 parts of ferric dithiocarbamate masterbatch and continue mixing for 4min to prepare a uniform functional additive premix. S2. Start the twin-screw extruder and set the temperature parameters for each section: Zone 1 135℃, Zone 2 150℃, Zone 3 160℃, Zone 4 165℃, and Die Head 155℃. After the temperature of each section stabilizes, adjust the screw speed to 225 r / min. Continuously add 45 parts of polybutylene adipate terephthalate and 25 parts of polycaprolactone through the main feed port. Add 6 parts of bamboo fiber and 3 parts of nano-montmorillonite through the side feed port at 1 / 3 of the distance from the die head. Add 2 / 3 of the distance from the die head... On the other side of the feed port, add 4 parts of tributyl citrate, 2.5 parts of maleic anhydride-grafted polybutylene adipate terephthalate and the functional additive premix prepared by S1; after the material is melted and sheared by the extruder and fully mixed, it is extruded from the die head to form strips; the strips are sent to a 27°C cold water bath for cooling, and then the surface moisture is dried by an air drying device with the air temperature set at 30°C and the air speed controlled at 4m / s. Finally, it is cut into 3mm long particles by a pelletizer to obtain composite masterbatch; S3. Start the blown film machine and set the temperatures for each section: 145℃ for barrel zone 1, 155℃ for barrel zone 2, 165℃ for barrel zone 3, and 160℃ for the die head. After the temperature stabilizes, adjust the screw speed to 100 r / min. Add the composite masterbatch to the blown film machine hopper. After the masterbatch melts in the barrel, it is extruded from the T-die head to form a 1.1 mm thick sheet. The sheet is preheated by a 72℃ preheating roller and then enters the stretching device. It is stretched longitudinally by a 2.5 times speed difference between the stretching rollers, with a rate gradient of 6 mm / s and a stretching temperature controlled at 72℃. After a 2.5s buffer after the longitudinal stretching, it is stretched laterally by 3 times at 83℃ with a rate gradient of 10 mm / s. The stretched film is then sent to a 92℃ heat setting device for setting, with a tension controlled at 0.6 MPa. It is then cooled by a 32℃ cooling roller and finally wound up by a winding device to obtain a 50 μm thick film. S4. Two portions of chitosan-sorbitol composite coating liquid were evenly sprayed onto the film surface using a spraying device, with a coating thickness of 6μm. The sprayed bag was then placed in an 80℃ drying device and dried for 28s to obtain the biodegradable express bag material.

[0027] Example 4: Preparation of modified bamboo fiber. The specific preparation steps are as follows: A1. Take 100g of dried bamboo fiber, add 300mL of phosphate buffer (pH=5.0), stir to disperse, then add 5g of cellulase, and react at 50℃ and 150r / min for 4h. After the reaction, filter and rinse three times with deionized water at 40℃ until the conductivity of the eluent is ≤200μS / cm. Then, transfer the fiber to 400g of 0.5% sodium bicarbonate solution, heat to 50℃ and soak until the pH of the fiber reaches 7.0. After filtration, add the fiber to 200mL of 5% β-cyclodextrin aqueous solution, stir at 60℃ and 200r / min for 2min, then add 1g of hexadecyltrimethylammonium bromide in two portions, continue stirring for 2h, then add 0.5g of disodium ethylenediaminetetraacetate and stir for another 1h. After the reaction, filter and vacuum dry the fiber at 80℃ for 6h to obtain the first modified bamboo fiber. A2. 100g of the first-modified bamboo fiber was added to 200mL of anhydrous ethanol and ultrasonically dispersed for 30min. Then, 4g of silane coupling agent KH-550 was added and refluxed at 70℃ for 3h. After filtration, the fiber was transferred to 30mL of 10% vanillin ethanol solution and 1mL of triethylamine was added. The mixture was stirred at 50℃ and 200r / min for 2h. After the reaction was completed, the fiber was washed three times with ethanol and vacuum dried at 60℃ for 5h to obtain the second-modified bamboo fiber. A3. Take 100g of the second modified bamboo fiber and add it to 300mL of deionized water. Stir at 300r / min to make a suspension. Add 8g of zinc nitrate, dissolve by sonication, and then add 220mL of 1.0mol / L 2-methylimidazolium ethanol solution. Stir at 30℃ and 300r / min for 4h. After the reaction is completed, filter and dry the product under vacuum at 70℃ for 8h to obtain the modified bamboo fiber.

[0028] Example 5: Preparation of modified bamboo fiber. The specific preparation steps are as follows: A1. Take 100g of dried bamboo fiber, add 350mL of phosphate buffer (pH=5.0), stir to disperse, then add 10g of cellulase, and react at 55℃ and 150r / min for 5h. After the reaction, filter and rinse three times with deionized water at 40℃ until the conductivity of the eluent is ≤200μS / cm. Then, transfer the fiber to 500g of 0.5% sodium bicarbonate solution, heat to 50℃ and soak until the pH of the fiber reaches 7.5. After filtration, add the fiber to 250mL of 5% β-cyclodextrin aqueous solution, stir at 60℃ and 200r / min for 2min, then add 2g of hexadecyltrimethylammonium bromide in two portions, continue stirring for 2h, then add 1.0g of disodium ethylenediaminetetraacetate and stir for another 1h. After the reaction, filter and vacuum dry the fiber at 80℃ for 6h to obtain the first modified bamboo fiber. A2. 100g of the first-modified bamboo fiber was added to 250mL of anhydrous ethanol and ultrasonically dispersed for 30min. Then, 6g of silane coupling agent KH-550 was added and refluxed at 75℃ for 3h. After filtration, the fiber was transferred to 50mL of 10% vanillin ethanol solution and 2mL of triethylamine was added. The mixture was stirred at 55℃ and 200r / min for 2h. After the reaction was completed, the fiber was washed three times with ethanol and vacuum dried at 60℃ for 5h to obtain the second-modified bamboo fiber. A3. Take 100g of the second modified bamboo fiber and add it to 350mL of deionized water. Stir at 300r / min to make a suspension. Add 10g of zinc nitrate and dissolve by sonication. Then add 280mL of 1.0mol / L 2-methylimidazolium ethanol solution. Stir at 35℃ and 300r / min for 4h. After the reaction is completed, filter and dry the product under vacuum at 70℃ for 8h to obtain the modified bamboo fiber.

[0029] Example 6: Preparation of modified nano-montmorillonite. The specific preparation steps are as follows: B1. Take 100g of nano-montmorillonite and add it to 400mL of deionized water. Stir at 500r / min for 30min to disperse it evenly. Then add 400mL of Tris-HCl buffer solution with pH=8.5 and sonicate for 1h until the suspension is stable. Add 5g of dopamine hydrochloride and stir at 200r / min for 6h at 25℃. Then add 30mL of 0.05mol / L silver nitrate solution and stir in the dark for 2h. Then add 0.3g of sodium ascorbate and continue to stir in the dark for 1h. Finally, centrifuge to separate the precipitate. Wash the precipitate twice with deionized water and vacuum dry at 50℃ for 6h to obtain the first modified nano-montmorillonite. B2. Take 100g of the first modified nano-montmorillonite and add 300mL of anhydrous ethanol. After ultrasonic dispersion for 30min, add 5g of polyethylene glycol 600 and reflux at 200r / min at 60℃ for 3h. After the reaction is completed, centrifuge and separate the precipitate. Wash the precipitate twice with anhydrous ethanol and vacuum dry at 60℃ for 5h to obtain the second modified nano-montmorillonite. B3. Take 100g of the second modified nano-montmorillonite and add 300mL of deionized water. Disperse ultrasonically for 30min until the suspension has no sedimentation. Add 5g of vanillin and 3g of melamine, stir until completely dissolved, then heat to 80℃ and stir at 200r / min for 6h. After the reaction is completed, centrifuge to separate the precipitate. Wash the precipitate twice with deionized water and dry it under vacuum at 80℃ for 8h to obtain the modified nano-montmorillonite.

[0030] Example 7: Preparation of modified nano-montmorillonite. The specific preparation steps are as follows: B1. Take 100g of nano-montmorillonite and add it to 450mL of deionized water. Stir at 500r / min for 30min to disperse it evenly. Then add 450mL of Tris-HCl buffer solution with pH=8.5 and sonicate for 1h until the suspension is stable. Add 7g of dopamine hydrochloride and stir at 200r / min at 30℃ for 6h. Then add 40mL of 0.05mol / L silver nitrate solution and stir in the dark for 2h. Then add 0.5g of sodium ascorbate and continue to stir in the dark for 1h. Finally, centrifuge to separate the precipitate. Wash the precipitate twice with deionized water and vacuum dry at 60℃ for 6h to obtain the first modified nano-montmorillonite. B2. Take 100g of the first-modified nano-montmorillonite and add 350mL of anhydrous ethanol. After ultrasonic dispersion for 30min, add 8g of polyethylene glycol 600 and reflux at 70℃ and 200r / min for 3h. After the reaction is completed, centrifuge and separate the precipitate. Wash the precipitate twice with anhydrous ethanol and vacuum dry at 60℃ for 5h to obtain the second-modified nano-montmorillonite. B3. Take 100g of the second modified nano-montmorillonite and add 350mL of deionized water. Disperse ultrasonically for 30min until the suspension has no sedimentation. Add 7g of vanillin and 4g of melamine, stir until completely dissolved, then heat to 80℃ and stir at 200r / min for 6h. After the reaction is completed, centrifuge to separate the precipitate. Wash the precipitate twice with deionized water and dry it under vacuum at 80℃ for 8h to obtain the modified nano-montmorillonite.

[0031] Comparative Example 1: Biodegradable express delivery bag material was prepared. The specific preparation steps are as follows: The remaining steps remain the same, except that the bamboo fiber in Example 3 is replaced with the modified bamboo fiber prepared in Example 4 to prepare a biodegradable express bag material.

[0032] Comparative Example 2: Biodegradable express delivery bag material was prepared. The specific preparation steps are as follows: The remaining steps remain the same, except that the nano-montmorillonite in Example 3 is replaced with the modified nano-montmorillonite prepared in Example 7 to prepare a biodegradable express delivery bag material.

[0033] Comparative Example 3: Biodegradable express delivery bag material was prepared. The specific preparation steps are as follows: The remaining steps remain unchanged, except that the bamboo fiber in Example 3 is replaced with the modified bamboo fiber prepared in Example 4, and the nano-montmorillonite is replaced with the modified nano-montmorillonite prepared in Example 7, to prepare a biodegradable express bag material.

[0034] Performance testing

[0035] According to the performance test results, among the seven indicators of tensile strength, elongation at break, 60-day composting degradation rate, puncture resistance, tensile strength retention rate after 7 days of thermo-oxidative aging at 100℃, antibacterial rate against Escherichia coli, and antibacterial rate against Staphylococcus aureus, the performance of Examples 1-3 showed a gradual optimization trend, with Example 3 exhibiting the best performance in all aspects, namely 24.1 MPa, 195.7%, 65.8%, 5.5 N, 72.8%, 42.3%, and 39.7%, respectively. When Comparative Example 1 alone replaced bamboo fiber with the modified bamboo fiber prepared in Example 4, or Comparative Example 2 alone replaced nano-montmorillonite with the modified nano-montmorillonite prepared in Example 7, Compared with Example 3, all properties of the modified bamboo fiber and the modified nano-montmorillonite were significantly improved. The modified bamboo fiber and the modified nano-montmorillonite achieved the best performance when the two specific modified components were replaced. The tensile strength reached 35.2 MPa, the elongation at break reached 289.5%, the 60-day compost degradation rate reached 85.7%, the puncture resistance reached 8.2 N, the tensile strength retention rate after 7 days of thermo-oxidative aging at 100℃ reached 90.5%, the antibacterial rate against Escherichia coli reached 92.8%, and the antibacterial rate against Staphylococcus aureus reached 90.3%. This shows that the synergistic effect of the specific modified bamboo fiber and the modified nano-montmorillonite can greatly enhance the mechanical properties, degradation performance, thermo-oxidative stability and antibacterial properties of the biodegradable express delivery bag material.

[0036] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A biodegradable express delivery bag material, characterized in that: It contains the following raw materials in parts by weight: 40-50 parts polybutylene adipate terephthalate, 20-30 parts polycaprolactone, 5-8 parts modified bamboo fiber, 2-4 parts modified nano-montmorillonite, 3-6 parts tributyl citrate, 0.1-0.3 parts antioxidant 1076, 1-2 parts ferric dithiocarbamate masterbatch, 2-3 parts maleic anhydride-grafted polybutylene adipate terephthalate, 0.3-0.6 parts zinc stearate, 0.1-0.3 parts baicalin, and 1-3 parts chitosan-sorbitol composite coating liquid.

2. The biodegradable express bag material according to claim 1, characterized in that: The carrier of the iron dithiocarbamate masterbatch is polybutylene adipate terephthalate, wherein the mass fraction of iron dithiocarbamate is 28-32%, and the particle size of the masterbatch is 2-4 mm; the total solid content of the chitosan-sorbitol composite coating liquid is 1 wt%, wherein the mass ratio of chitosan to sorbitol is 3:

2.

3. The biodegradable express bag material according to claim 1, characterized in that: The baicalein is a spray-dried powder with a particle size D50≤5μm, which is coated with 0.5wt% chitosan aqueous solution, and the coating thickness is 50-100nm.

4. The biodegradable express bag material according to claim 1, characterized in that: The modified bamboo fiber is prepared using the following specific steps: A1. Take dried bamboo fiber, add phosphate buffer solution with pH=5.0, stir to disperse, then add cellulase, and react at 50-55℃ and 150r / min for 4-5 hours. After the reaction, filter and rinse three times with deionized water at 40℃ until the conductivity of the eluent is ≤200μS / cm. Then, transfer the fiber to a 0.5% sodium bicarbonate solution, heat to 50℃ and soak until the pH of the fiber reaches 7.0-7.5 when sampled. After filtration, add the fiber to a 5% β-cyclodextrin aqueous solution, stir at 60℃ and 200r / min for 2 minutes, then add hexadecyltrimethylammonium bromide in two portions and continue stirring for 2 hours. Then add disodium ethylenediaminetetraacetate and stir for another hour. After the reaction, filter and vacuum dry the fiber at 80℃ for 6 hours to obtain the first modified bamboo fiber. A2. The first modified bamboo fiber was added to anhydrous ethanol and ultrasonically dispersed for 30 min. Then, silane coupling agent KH-550 was added, and the mixture was refluxed at 70-75℃ for 3 h. After filtration, the fiber was transferred to a 10% (w / w) vanillin ethanol solution, and triethylamine was added. The mixture was stirred at 50-55℃ and 200 r / min for 2 h. After the reaction was completed, the fiber was washed three times with ethanol and vacuum dried at 60℃ for 5 h to obtain the second modified bamboo fiber. A3. Take the second modified bamboo fiber and add it to deionized water. Stir at 300 r / min to make a suspension. Add zinc nitrate, dissolve by ultrasonication, and then add dropwise a 1.0 mol / L 2-methylimidazolium ethanol solution. Stir at 30-35℃ and 300 r / min for 4 h. After the reaction is completed, filter and dry the product under vacuum at 70℃ for 8 h to obtain modified bamboo fiber.

5. The biodegradable express bag material according to claim 4, characterized in that: The ratio of dried bamboo fiber, phosphate buffer, cellulase, sodium bicarbonate solution, β-cyclodextrin aqueous solution, hexadecyltrimethylammonium bromide, and disodium EDTA in A1 is 100g:300-350mL:5-10g:400-500g:200-250mL:1-2g:0.5-1.0g; wherein the cellulase activity is 1000U / g. The ratio of the first modified bamboo fiber, anhydrous ethanol, silane coupling agent KH-550, vanillin ethanol solution, and triethylamine in A2 is 100g: 200-250mL: 4-6g: 30-50mL: 1-2mL. The ratio of the amount of the second modified bamboo fiber, deionized water, zinc nitrate, and 2-methylimidazolium ethanol solution in A3 is 100g: 300-350mL: 8-10g: 220-280mL.

6. The biodegradable express bag material according to claim 1, characterized in that: The modified nano-montmorillonite is prepared using the following specific steps: B1. Add nano-montmorillonite to deionized water and stir at 500 rpm for 30 min to disperse evenly. Then add tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution at pH 8.5 and sonicate for 1 h until the suspension is stable. Add dopamine hydrochloride and stir at 200 rpm for 6 h at 25-30 °C. Then add 0.05 mol / L silver nitrate solution and stir in the dark for 2 h. Add sodium ascorbate and continue stirring in the dark for 1 h. Finally, centrifuge to separate the precipitate. Wash the precipitate twice with deionized water and vacuum dry at 50-60 °C for 6 h to obtain the first modified nano-montmorillonite. B2. Take the first modified nano-montmorillonite and add anhydrous ethanol. After ultrasonic dispersion for 30 min, add polyethylene glycol 600 and reflux at 200 r / min at 60-70℃ for 3 h. After the reaction is completed, centrifuge and separate the precipitate. Wash the precipitate twice with anhydrous ethanol and vacuum dry at 60℃ for 5 h to obtain the second modified nano-montmorillonite. B3. Take the second modified nano-montmorillonite and add it to deionized water. Disperse it ultrasonically for 30 minutes until there is no sedimentation in the suspension. Add vanillin and melamine, stir until completely dissolved, then heat to 80℃ and stir at 200 r / min for 6 hours. After the reaction is completed, centrifuge to separate the precipitate. Wash the precipitate twice with deionized water and dry it under vacuum at 80℃ for 8 hours to obtain the modified nano-montmorillonite.

7. The biodegradable express bag material according to claim 6, characterized in that: The ratio of nano-montmorillonite, deionized water, tris(hydroxymethyl)aminomethane-hydrochloric acid buffer, dopamine hydrochloride, silver nitrate solution, and sodium ascorbate in B1 is 100g: 400-450mL: 400-450mL: 5-7g: 30-40mL: 0.3-0.5g; The ratio of the first modified nano-montmorillonite, anhydrous ethanol, and polyethylene glycol 600 in B2 is 100g: 300-350mL: 5-8g; The ratio of the second modified nano-montmorillonite, deionized water, vanillin, and melamine in B3 is 100g: 300-350mL: 5-7g: 3-4g.

8. A method for preparing a biodegradable express delivery bag material, characterized in that: Specifically, it includes the following steps: S1. Place polybutylene adipate terephthalate and polycaprolactone granules into a vacuum drying oven and dry at 85-90℃ for 5-6 hours. Place modified bamboo fiber and modified nano-montmorillonite into another vacuum drying oven and dry at 75-80℃ for 4 hours. Take 0.1-0.3 parts of antioxidant 1076, 0.3-0.6 parts of zinc stearate, and 0.1-0.3 parts of baicalin and mix them in a high-speed mixer at 50-60℃ and 1500-2000r / min for 5-8 minutes. Then add 1.0-2.0 parts of ferric dithiocarbamate masterbatch and continue mixing for 3-5 minutes to prepare a uniform functional additive premix. S2. Start the twin-screw extruder and set the temperature parameters for each section: Zone 1 130-140℃, Zone 2 145-155℃, Zone 3 155-165℃, Zone 4 160-170℃, and Die head 150-160℃. After the temperature of each section stabilizes, adjust the screw speed to 200-250 r / min. Continuously add 40-50 parts of polybutylene adipate terephthalate and 20-30 parts of polycaprolactone through the main feed port. Add 5-8 parts of modified bamboo fiber and 2-4 parts of modified nanofiber through the side feed port located 1 / 3 of the way from the die head. Montmorillonite; 3-6 parts of tributyl citrate, 2-3 parts of maleic anhydride-grafted polybutylene adipate terephthalate and S1 prepared functional additive premix are added to the feed port on the other side, 2 / 3 of the distance from the die head; after the material is melted and sheared by the extruder and fully mixed, it is extruded from the die head to form strips; the strips are sent to a cold water tank at 25-30℃ to cool, and then the surface moisture is dried by an air drying device with the air temperature set at 25-35℃ and the air speed controlled at 3-5m / s. Finally, it is cut into 3-4mm long particles by a pelletizer to obtain composite masterbatch; S3. Start the blown film machine and set the temperatures for each section: Zone 1 of the barrel 140-150℃, Zone 2 of the barrel 150-160℃, Zone 3 of the barrel 160-170℃, and the die head 155-165℃. After the temperature stabilizes, adjust the screw speed to 90-110 r / min. Add the composite masterbatch to the blown film machine hopper. After the masterbatch melts in the barrel, it is extruded from the T-die head to form a sheet material with a thickness of 1.0-1.2 mm. The sheet material is then passed through a 70-7... The film is preheated at 5°C by a preheating roller and then enters the stretching device: longitudinal stretching is performed by a speed difference of 2.5 times between the stretching rollers, and the stretching temperature is controlled at 70-75°C. After the longitudinal stretching is completed and buffered for 2-3 seconds, transverse stretching is performed at 80-85°C by 3 times. The stretched film is then sent to a heat setting device at 90-95°C for setting, and then cooled by a cooling roller at 30-35°C. Finally, it is wound up by a winding device to obtain a film with a thickness of 40-60μm. S4. Spray 1-3 parts of chitosan-sorbitol composite coating liquid evenly onto the film surface using a spraying device, with a coating thickness of 5-8μm. Then, put the coated bag into an 80℃ drying device and dry it for 25-30 seconds to finally obtain the biodegradable express bag material.

9. The method for preparing a biodegradable express delivery bag material according to claim 8, characterized in that: In S3, the longitudinal stretching rate gradient is 5-8 mm / s, the transverse stretching rate gradient is 8-12 mm / s, and the tension control in the heat setting device is 0.5-0.8 MPa.

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