Biodegradable PBAT lamination resin, preparation method and application

Abstract

This invention discloses a biodegradable PBAT coating resin, its preparation method, and its applications, belonging to the field of polymer material modification technology. The specific preparation method involves: PBAT-M copolymers are prepared by polycondensation of terephthalic acid, adipic acid, 1,4-butanediol, and 2-methyl-1,3-propanediol under a catalyst; the PBAT-M copolymer, initiator, and maleic anhydride are mixed and melt-extruded to obtain maleic anhydride-grafted modified PBAT-M copolymers; silica nanoparticles are dispersed in an acetic acid solution of chitosan to obtain chitosan surface-functionalized silica nanoparticles; the maleic anhydride-grafted modified PBAT-M copolymer, chitosan surface-functionalized silica nanoparticles, flow modifier, and PBAT are mixed and melt-extruded to obtain a biodegradable PBAT coating resin. This invention improves melt flowability by introducing a side-methyl-containing comonomer, enhances interfacial adhesion to paper substrates through maleic anhydride grafting, and imparts antibacterial and reinforcing properties to the material through chitosan surface-functionalized nanoparticles.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification technology, and in particular to biodegradable PBAT coating resin, its preparation method and application. Background Technology

[0002] In recent years, with the increasing global awareness of environmental protection, the environmental pollution caused by the difficulty in degrading traditional plastic products has received growing attention. Biodegradable materials, because they can be broken down into harmless substances such as water and carbon dioxide by microorganisms in the natural environment, have become an important direction for replacing traditional plastics. Among them, polybutylene terephthalate (PBAT), as a typical fully biodegradable aliphatic-aromatic copolyester, has good flexibility, ductility, and biodegradability, and has been widely used in packaging, agricultural films, and disposable products.

[0003] In the packaging industry, paper-based composite materials are widely used due to their advantages such as lightweight, printability, and easy recyclability. Surface coating is a crucial process for ensuring the oil and water resistance of packaging. Currently, most coating materials on the market still use non-degradable polyolefin resins such as polyethylene (PE) and polypropylene (PP), which severely restricts the overall degradability and environmental friendliness of paper-based packaging. Currently, green and environmentally friendly biodegradable coating materials mainly use polylactic acid (PLA) resin. However, PLA resin has low melt strength and poor film-forming properties. To achieve the necessary barrier and mechanical properties, its coating basis weight usually needs to be above 30 g / m², which directly leads to a significant increase in raw material costs. In contrast, PBAT has superior ductility and film-forming properties, and its raw material cost is much lower than PLA. Therefore, developing biodegradable PBAT coated packaging products suitable for existing coating processes has become an important technological requirement in the field of green packaging materials.

[0004] However, directly applying PBAT to paper-based coating still faces technical bottlenecks. First, PBAT resin melt has poor fluidity and insufficient wetting ability on paper substrates, affecting coating efficiency and film quality. Second, PBAT has low surface energy and weak polarity, resulting in poor compatibility with paper surfaces rich in polar groups such as hydroxyl groups, leading to insufficient adhesion strength and problems such as coating layer peeling and leakage, affecting the sealing performance and reliability of packaging. In addition, PBAT coating materials still need improvement in terms of mechanical strength, hydrophobicity, and antibacterial properties.

[0005] Therefore, developing a biodegradable PBAT coating resin that can balance excellent melt flowability, high interfacial adhesion strength, and good antibacterial properties is of great significance for promoting the large-scale application of PBAT coating resin in the field of green paper-plastic composite packaging materials. Summary of the Invention

[0006] Based on the technical problems existing in the background technology, the present invention proposes a biodegradable PBAT coating resin, its preparation method and application. The melt flowability is improved by introducing a comonomer containing side methyl groups, the interfacial adhesion with the paper substrate is improved by grafting maleic anhydride, and the antibacterial and reinforcing properties of the material are endowed by chitosan surface functionalized nanoparticles.

[0007] The method for preparing the biodegradable PBAT coating resin proposed in this invention comprises the following steps:

[0008] S1: The product obtained by polycondensation reaction of terephthalic acid, adipic acid, 1,4-butanediol and 2-methyl-1,3-propanediol under the action of a catalyst is called PBAT-M copolymer.

[0009] S2: After mixing the PBAT-M copolymer, initiator and maleic anhydride, the mixture is melt-extruded to obtain the maleic anhydride-grafted modified PBAT-M copolymer.

[0010] S3: Disperse silica nanoparticles in an acetic acid solution of chitosan to obtain chitosan surface-functionalized silica nanoparticles.

[0011] S4: Maleic anhydride-grafted modified PBAT-M copolymer, chitosan surface-functionalized silica nanoparticles, flow modifier and PBAT are mixed and melt-extruded to obtain biodegradable PBAT coating resin.

[0012] Preferably, the catalyst in S1 is a mixture of tetrabutyl titanate and triethyl phosphate, wherein the molar ratio of titanium to phosphorus is 2-6:1; and the amount of catalyst added is 100-200 ppm.

[0013] Preferably, the molar ratio of terephthalic acid, adipic acid, 1,4-butanediol and 2-methyl-1,3-propanediol in S1 is 0.46-0.49:0.51-0.54:1.12-1.36:0.24-0.48.

[0014] Preferably, the conditions for the polycondensation reaction in S1 are: temperature 240-260℃, time 2.5-4h, and vacuum pressure 150-300Pa.

[0015] Preferably, in S2, the amount of initiator added is 0.5-1 wt% based on the mass of the PBAT-M copolymer, the initiator is dicumyl peroxide, and the amount of maleic anhydride added is 1-3 wt%.

[0016] And / or, the melt extrusion temperature is 150-170℃, and the screw speed is 50-200 rpm;

[0017] And / or, the grafting rate of the maleic anhydride-grafted modified PBAT-M copolymer is 0.8%~1.4%.

[0018] Preferably, the mass ratio of chitosan to silica nanoparticles in S3 is 1.2-2:1;

[0019] And / or, the molecular weight of chitosan is 2 × 10⁻⁶. 5 -3×10 5 Da;

[0020] And / or, the chitosan concentration in the acetic acid solution is 0.6%-1% (w / v), and the solvent is a 10% (v / v) aqueous acetic acid solution.

[0021] Preferably, the flow modifier in S4 is selected from at least one of stearic acid, zinc stearate, calcium stearate, and ethylene bis-stearamide;

[0022] And / or, the mass ratio of maleic anhydride graft-modified PBAT-M copolymer, chitosan surface-functionalized silica nanoparticles, flow modifier and PBAT is 5-10:1-5:0.5-1:85-95.

[0023] Preferably, the conditions for melt extrusion in S4 are: screw speed of 100-200 rpm, feeding frequency of 3-5 Hz, and the temperature of each zone of the extruder is set as follows: 150℃ for zones 1 to 3, 155℃ for zones 4 to 6, 160℃ for zones 7 to 9, and 155℃ for zones 10 to 12.

[0024] The present invention proposes a biodegradable PBAT coating resin, which is prepared by the above-described method.

[0025] The present invention proposes the application of the biodegradable PBAT coating resin described above in green paper-plastic composite packaging materials.

[0026] Beneficial technical effects of the present invention:

[0027] (1) In this invention, 2-methyl-1,3-propanediol is used as a comonomer. Side methyl groups are introduced into the PBAT molecular chain. The steric hindrance effect of the side methyl groups inhibits the regular arrangement of chain segments, thereby improving the melt flowability and the wetting and spreading ability of the substrate. At the same time, the tertiary carbon atoms introduced by the comonomer provide more active sites for the maleic anhydride grafting reaction, which greatly improves the grafting efficiency. The introduction of maleic anhydride polar groups effectively improves the surface polarity of the resin, solves the problem of low surface energy of PBAT and poor compatibility with paper surfaces rich in polar groups, thereby enhancing the adhesion strength between the coating layer and the paper substrate.

[0028] (2) This invention achieves synergistic enhancement of the composite material in terms of antibacterial properties, hydrophobicity, and mechanical properties by functionalizing the surface of silica nanoparticles with chitosan and then blending them with PBAT coating resin. The abundant silanol groups on the surface of silica nanoparticles can form a stable hydrogen bond network with the ester groups and terminal carboxyl groups in the PBAT molecular chain, effectively improving interfacial compatibility and thus significantly improving the mechanical strength and structural stability of the composite material; chitosan endows the material with excellent natural antibacterial activity, so that the final material has high hydrophobicity, strong mechanical properties and broad-spectrum antibacterial ability, improving its hygiene safety and applicability in green paper-plastic composite packaging applications. Attached Figure Description

[0029] Figure 1 This is a synthetic route diagram for the maleic anhydride graft-modified PBAT-M copolymer proposed in this invention. Detailed Implementation

[0030] The present invention will be further explained below with reference to specific embodiments.

[0031] In the embodiments of this invention, terephthalic acid, adipic acid, 1,4-butanediol, 2-methyl-1,3-propanediol, tetrabutyl titanate, triethyl phosphate, dicumyl peroxide, maleic anhydride, silica nanoparticles, chitosan, zinc stearate, ethylene bis-stearamide (EBS), and polybutylene terephthalate-adipate (PBAT) are all commercially available.

[0032] The PBAT in this embodiment of the invention has a melt index (190℃, 2.16kg) of 5.4g / 10min, a melting point of 112.9℃, and a carboxyl content of 14.3mol / t, and was purchased from Zhonghua Donghua Tianye New Materials Co., Ltd.

[0033] Example 1

[0034] Under nitrogen protection, 81.4 g (0.49 mol) of terephthalic acid, 74.5 g (0.51 mol) of adipic acid, 122.6 g (1.36 mol) of 1,4-butanediol, 21.6 g (0.24 mol) of 2-methyl-1,3-propanediol, 214 mg of tetrabutyl titanate catalyst, and 28.5 mg of triethyl phosphate were added to the polymerization reactor. First, a prepolymerization reaction was carried out at 220 °C, with stirring and evaporation of the generated water until the water output reached 80% of the theoretical yield. Then, the system was heated to 260 °C, and a vacuum was gradually drawn until the pressure was below 300 Pa for a polycondensation reaction of 3 hours. After the reaction, the product was discharged from the bottom of the reactor, cooled, pelletized, and vacuum dried at 80 °C for 6 hours to obtain PBAT-M copolymer particles.

[0035] Weigh 200g of the above PBAT-M copolymer, 2g of dicumyl peroxide, and 4g of maleic anhydride, mix them evenly in a high-speed mixer, and add them to a twin-screw extruder. Melt extrusion is carried out at a screw barrel temperature of 160℃ and a rotation speed of 50 rpm. After cooling and pelletizing, the extrudate is dissolved in dichloromethane, and then anhydrous methanol is slowly poured in. The precipitate is collected by filtration, washed three times with methanol, and dried under vacuum at 80℃ for 6 hours to obtain maleic anhydride grafted modified PBAT-M copolymer with a grafting rate of 1.2%.

[0036] A 0.6% (w / v) chitosan-acetic acid solution (solvent: 10% v / v aqueous acetic acid) was prepared. 2 L of the chitosan solution was weighed and mixed with 10 g of silica nanoparticle powder. The mixture was first sonicated for 6 hours, followed by mechanical stirring at room temperature for 24 hours. After the reaction was complete, the solid was collected by centrifugation, washed with deionized water until neutral, and then vacuum dried at 60 °C for 8 hours to obtain chitosan-functionalized silica nanoparticles.

[0037] Weigh out 0.1 kg of maleic anhydride-grafted modified PBAT-M copolymer, 0.04 kg of chitosan surface-functionalized silica nanoparticle powder, 0.01 kg of flow modifier EBS, and 1.85 kg of PBAT base resin. Mix them evenly in a high-speed mixer. Add the mixture to a twin-screw extruder, set the screw speed to 100 rpm, the feeding frequency to 4 Hz, and the temperatures of each zone as follows: zones 1-3 150℃, zones 4-6 155℃, zones 7-9 160℃, and zones 10-12 155℃. After melt blending and extrusion, cool, pelletize, and dry to obtain a biodegradable PBAT coating resin. Composite this resin with a paper substrate using a coating machine to obtain a coated paper-plastic composite material.

[0038] Example 2

[0039] Under nitrogen protection, 76.4 g (0.46 mol) of terephthalic acid, 78.9 g (0.54 mol) of adipic acid, 100.9 g (1.12 mol) of 1,4-butanediol, 43.3 g (0.48 mol) of 2-methyl-1,3-propanediol, 143 mg of tetrabutyl titanate catalyst, and 19 mg of triethyl phosphate were added to the polymerization reactor. First, a prepolymerization reaction was carried out at 220 °C, with stirring and evaporation of the generated water until the water output reached 80% of the theoretical yield. Then, the system was heated to 260 °C, and a vacuum was gradually drawn until the pressure was below 300 Pa for a polycondensation reaction of 2.5 hours. After the reaction, the product was discharged from the bottom of the reactor, cooled, pelletized, and vacuum dried at 80 °C for 6 hours to obtain PBAT-M copolymer particles.

[0040] Weigh 200g of the above PBAT-M copolymer, 2g of dicumyl peroxide, and 2g of maleic anhydride, mix them evenly in a high-speed mixer, add them to a twin-screw extruder, and melt extrude them at a screw barrel temperature of 160℃ and a speed of 50 rpm. After cooling and pelletizing, the extrudate is dissolved in dichloromethane, and then anhydrous methanol is slowly poured in. The precipitate is collected by filtration, washed three times with methanol, and dried under vacuum at 80℃ for 6 hours to obtain maleic anhydride grafted modified PBAT-M copolymer with a grafting rate of 0.8%.

[0041] Prepare a 0.8% (w / v) chitosan-acetic acid solution (solvent: 10% v / v aqueous acetic acid solution). Weigh 2 L of the above chitosan solution and mix it with 10 g of silica nanoparticle powder. First, sonicate the mixture for 6 hours, then mechanically stir it at room temperature for 24 hours. After the reaction is complete, collect the solid by centrifugation, wash it with deionized water until neutral, and dry it under vacuum at 60 °C for 8 hours to obtain chitosan-functionalized silica nanoparticles.

[0042] Weigh out 0.16 kg of maleic anhydride-grafted modified PBAT-M copolymer, 0.08 kg of chitosan surface-functionalized silica nanoparticle powder, 0.02 kg of flow modifier zinc stearate, and 1.74 kg of PBAT base resin. Mix them evenly in a high-speed mixer. Add the mixture to a twin-screw extruder, set the screw speed to 100 rpm, the feeding frequency to 4 Hz, and the temperatures of each zone as follows: zones 1-3 150℃, zones 4-6 155℃, zones 7-9 160℃, and zones 10-12 155℃. After melt blending and extrusion, cool, pelletize, and dry to obtain a biodegradable PBAT coating resin. Composite the resin with a paper substrate using a coating machine to obtain a coated paper-plastic composite material.

[0043] Example 3

[0044] Under nitrogen protection, 79.7 g (0.48 mol) of terephthalic acid, 76 g (0.52 mol) of adipic acid, 115.4 g (1.28 mol) of 1,4-butanediol, 28.8 g (0.32 mol) of 2-methyl-1,3-propanediol, 285 mg of tetrabutyl titanate catalyst, and 38 mg of triethyl phosphate were added to the polymerization reactor. First, a prepolymerization reaction was carried out at 220 °C, with stirring and evaporation of the generated water until the water output reached 80% of the theoretical yield. Then, the system was heated to 260 °C, and a vacuum was gradually applied until the pressure was below 300 Pa for a polycondensation reaction of 4 hours. After the reaction, the product was discharged from the bottom of the reactor, cooled, pelletized, and vacuum dried at 80 °C for 6 hours to obtain PBAT-M copolymer particles.

[0045] Weigh 200g of the above PBAT-M copolymer, 2g of dicumyl peroxide, and 6g of maleic anhydride, mix them evenly in a high-speed mixer, and add them to a twin-screw extruder. Melt extrusion is carried out at a screw barrel temperature of 160℃ and a speed of 50 rpm. After cooling and pelletizing, the extrudate is dissolved in dichloromethane, and then anhydrous methanol is slowly poured in. The precipitate is collected by filtration, washed three times with methanol, and dried under vacuum at 80℃ for 6 hours to obtain maleic anhydride grafted modified PBAT-M copolymer with a grafting rate of 1.4%.

[0046] A 1% (w / v) chitosan-acetic acid solution (solvent: 10% v / v aqueous acetic acid) was prepared. 2 L of the chitosan solution was weighed and mixed with 10 g of silica nanoparticle powder. The mixture was first sonicated for 6 hours, followed by mechanical stirring at room temperature for 24 hours. After the reaction was complete, the solid was collected by centrifugation, washed with deionized water until neutral, and then vacuum dried at 60 °C for 8 hours to obtain chitosan-functionalized silica nanoparticles.

[0047] Weigh out 0.2 kg of maleic anhydride-grafted modified PBAT-M copolymer, 0.1 kg of chitosan surface-functionalized silica nanoparticle powder, 0.016 kg of flow modifier calcium stearate, and 1.684 kg of PBAT base resin. Mix them evenly in a high-speed mixer. Add the mixture to a twin-screw extruder, set the screw speed to 100 rpm, the feeding frequency to 4 Hz, and the temperatures of each zone as follows: zones 1-3 150℃, zones 4-6 155℃, zones 7-9 160℃, and zones 10-12 155℃. After melt blending and extrusion, cool, pelletize, and dry to obtain a biodegradable PBAT coating resin. Composite this resin with a paper substrate using a coating machine to obtain a coated paper-plastic composite material.

[0048] Comparative Example 1

[0049] Weigh 1.99 kg of PBAT base resin and 0.01 kg of flow modifier zinc stearate, mix them evenly in a high-speed mixer, add the mixture to a twin-screw extruder, set the screw speed to 100 rpm, the feeding frequency to 4 Hz, and the temperatures of each zone as follows: 150℃ for zones 1 to 3, 155℃ for zones 4 to 6, 160℃ for zones 7 to 9, and 155℃ for zones 10 to 12. After melt blending and extrusion, cool, pelletize, and dry to obtain the resin. Then, use a coating machine to laminate the resin with a paper substrate to obtain a coated paper-plastic composite material.

[0050] Comparative Example 2

[0051] A 0.6% (w / v) chitosan-acetic acid solution (solvent: 10% v / v aqueous acetic acid) was prepared. 2 L of the chitosan solution was weighed and mixed with 10 g of silica nanoparticle powder. The mixture was first sonicated for 6 hours, followed by mechanical stirring at room temperature for 24 hours. After the reaction was complete, the solid was collected by centrifugation, washed with deionized water until neutral, and then vacuum dried at 60 °C for 8 hours to obtain chitosan-functionalized silica nanoparticles.

[0052] Weigh 0.08 kg of chitosan surface-functionalized silica nanoparticle powder, 0.01 kg of flow modifier zinc stearate, and 1.91 kg of PBAT base resin. Mix them evenly in a high-speed mixer. Add the mixture to a twin-screw extruder, set the screw speed to 100 rpm, the feeding frequency to 4 Hz, and the temperatures of each zone as follows: zones 1-3 150℃, zones 4-6 155℃, zones 7-9 160℃, and zones 10-12 155℃. After melt blending and extrusion, cool, pelletize, and dry to obtain the resin. Use the resin to laminate it with a paper substrate to obtain a laminated paper-plastic composite material.

[0053] Comparative Example 3

[0054] Under nitrogen protection, 81.4 g (0.49 mol) of terephthalic acid, 74.5 g (0.51 mol) of adipic acid, 122.6 g (1.36 mol) of 1,4-butanediol, 21.6 g (0.24 mol) of 2-methyl-1,3-propanediol, 214 mg of tetrabutyl titanate catalyst, and 28.5 mg of triethyl phosphate were added to the polymerization reactor. First, a prepolymerization reaction was carried out at 220 °C, with stirring and evaporation of the generated water until the water output reached 80% of the theoretical yield. Then, the system was heated to 260 °C, and a vacuum was gradually drawn until the pressure was below 300 Pa for a polycondensation reaction of 3 hours. After the reaction, the product was discharged from the bottom of the reactor, cooled, pelletized, and vacuum dried at 80 °C for 6 hours to obtain PBAT-M copolymer particles.

[0055] A 0.6% (w / v) chitosan-acetic acid solution (solvent: 10% v / v aqueous acetic acid) was prepared. 2 L of the chitosan solution was weighed and mixed with 10 g of silica nanoparticle powder. The mixture was first sonicated for 6 hours, followed by mechanical stirring at room temperature for 24 hours. After the reaction was complete, the solid was collected by centrifugation, washed with deionized water until neutral, and then vacuum dried at 60 °C for 8 hours to obtain chitosan-functionalized silica nanoparticles.

[0056] Weigh 0.1 kg of PBAT-M copolymer, 0.04 kg of chitosan surface-functionalized silica nanoparticle powder, 0.01 kg of flow modifier EBS, and 1.85 kg of PBAT base resin. Mix them evenly in a high-speed mixer. Add the mixture to a twin-screw extruder, set the screw speed to 100 rpm, the feeding frequency to 4 Hz, and the temperatures of each zone as follows: zones 1-3 150℃, zones 4-6 155℃, zones 7-9 160℃, and zones 10-12 155℃. After melt blending and extrusion, cool, pelletize, and dry to obtain a biodegradable PBAT coating resin. Composite this resin with a paper substrate using a coating machine to obtain a coated paper-plastic composite material.

[0057] The biodegradable PBAT coating resins and their paper-plastic composites prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests according to relevant national standards. The test results are shown in Table 1. All data are the average values ​​of three parallel tests. The test methods are as follows: melt flow index according to GB / T 3682.1-2018 (test conditions 190℃, 2.16 kg), tensile properties according to GB / T 1040.2-2022 (dumbbell-shaped specimen, tensile rate 50 mm / min), and peel strength according to GB / T 8808-1988.

[0058] Table 1. Performance test results of the biodegradable coating resins and their paper-plastic composites prepared in the examples and comparative examples.

[0059] sample Melt index (g / 10min) Tensile strength (MPa) Elongation at break (%) Peel force (N / 15mm) <![CDATA[Coating weight (g / m 2 )]]> Example 1 15.7 26.2 510 1.1 30 Example 2 18.4 27.1 485 1.3 30 Example 3 17.3 29.8 532 1.4 30 Comparative Example 1 13.2 22.5 412 0.6 30 Comparative Example 2 14.5 24.3 473 0.8 30 Comparative Example 3 16.1 27.0 530 0.7 30

[0060] According to the performance test results shown in Table 1, Examples 1-3 of the present invention exhibit significant comprehensive performance advantages over Comparative Examples 1-3 in terms of melt flowability, mechanical properties, and interfacial adhesion. This is mainly due to the synergistic design of the components in the present invention: on the one hand, by introducing a 2-methyl-1,3-propanediol comonomer containing side methyl groups into the PBAT molecular backbone, the melt viscosity is effectively reduced, improving the flowability of the resin during the coating process; simultaneously, the tertiary carbon active sites provided by this comonomer promote the grafting reaction of maleic anhydride, and the introduced polar groups significantly enhance the interfacial adhesion between the resin and paper. In addition, the introduction of chitosan-functionalized silica nanoparticles exerts an excellent composite reinforcement effect through interfacial hydrogen bonding, further improving the tensile strength of the material.

[0061] In summary, the biodegradable PBAT coating resin prepared by this invention outperforms the unmodified or single-modified control group in many key properties, significantly overcoming the technical bottlenecks of existing PBAT materials in coating applications and showing good application prospects.

[0062] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application. The scope of this application is defined by the appended claims and their equivalents, all of which should be included within the protection scope of this application.

Claims

1. Process for the preparation of biodegradable PBAT cast film resin, characterized in that, The steps are as follows: S1: The product obtained by polycondensation reaction of terephthalic acid, adipic acid, 1,4-butanediol and 2-methyl-1,3-propanediol under the action of a catalyst is called PBAT-M copolymer. S2: After mixing the PBAT-M copolymer, initiator and maleic anhydride, the mixture is melt-extruded to obtain the maleic anhydride-grafted modified PBAT-M copolymer. S3: Disperse silica nanoparticles in an acetic acid solution of chitosan to obtain chitosan surface-functionalized silica nanoparticles. S4: Maleic anhydride graft-modified PBAT-M copolymer, chitosan surface-functionalized silica nanoparticles, flow modifier and PBAT are mixed and melt-extruded to obtain biodegradable PBAT coating resin. The flow modifier in S4 is selected from at least one of stearic acid, zinc stearate, calcium stearate, and ethylene bis-stearamide; The mass ratio of maleic anhydride-grafted modified PBAT-M copolymer, chitosan surface-functionalized silica nanoparticles, flow modifier, and PBAT is 5-10:1-5:0.5-1:85-95.

2. The method for preparing the biodegradable PBAT coating resin according to claim 1, characterized in that, The catalyst in S1 is a mixture of tetrabutyl titanate and triethyl phosphate, wherein the molar ratio of titanium to phosphorus is 2-6:1; the amount of catalyst added is 100-200 ppm.

3. The method for preparing the biodegradable PBAT coating resin according to claim 1, characterized in that, The molar ratio of terephthalic acid, adipic acid, 1,4-butanediol and 2-methyl-1,3-propanediol in S1 is 0.46-0.49:0.51-0.54:1.12-1.36:0.24-0.

48.

4. The method for preparing the biodegradable PBAT coating resin according to claim 1, characterized in that, The conditions for the polycondensation reaction in S1 are: temperature 240-260℃, time 2.5-4h, and vacuum pressure 150-300Pa.

5. The method for preparing the biodegradable PBAT coating resin according to claim 1, characterized in that, In S2, based on the mass of the PBAT-M copolymer, the amount of initiator added is 0.5-1 wt%, and the amount of maleic anhydride added is 1-3 wt%. And / or, the melt extrusion temperature is 150-170℃, and the screw speed is 50-200 rpm; And / or, the grafting rate of the maleic anhydride-grafted modified PBAT-M copolymer is 0.8%~1.4%.

6. The method for preparing the biodegradable PBAT coating resin according to claim 1, characterized in that, The mass ratio of chitosan to silica nanoparticles in S3 is 1.2-2:1; And / or, the molecular weight of chitosan is 2 × 10⁻⁶. 5 -3×10 5 Da; And / or, the chitosan concentration in the acetic acid solution is 0.6%-1% (w / v), and the solvent is a 10% (v / v) aqueous acetic acid solution.

7. The method for preparing the biodegradable PBAT coating resin according to claim 1, characterized in that, The conditions for melt extrusion in S4 are: screw speed of 100-200 rpm, feeding frequency of 3-5 Hz, and temperature settings for each zone of the extruder as follows: 150℃ for zones 1 to 3, 155℃ for zones 4 to 6, 160℃ for zones 7 to 9, and 155℃ for zones 10 to 12.

8. Biodegradable PBAT cast film resin characterized in that, It is prepared by the preparation method according to any one of claims 1-7.

9. The application of the biodegradable PBAT coating resin as described in claim 8 in green paper-plastic composite packaging materials.

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