Biodegradable graphene / PBAT composite packaging bag and preparation method thereof

Abstract

The invention provides a biodegradable graphene / PBAT composite packaging bag and a preparation method thereof. The method comprises the following steps: S1, heating and calcining rice husks in an air furnace to obtain rice husk ash; s2, mixing the rice hull ash with potassium hydroxide, and reacting at 700-900 DEG C; s3, adding a product obtained in the step S2 into lime milk for full reaction, precipitating calcium carbonate among graphene, then filtering, cleaning to be neutral, and drying to obtain a calcium carbonate / graphene composite material; s4, blending the calcium carbonate / graphene composite material with a PBAT master batch, performing melt extrusion by using a double-screw extruder, performing air cooling, and performing pelletizing for standby application to obtain a calcium carbonate / graphene / PBAT composite master batch; and S5, preparing the full-biodegradable graphene-based PBAT film from the calcium carbonate / graphene / PBAT composite master batch by adopting a film blowing method, and then preparing the packaging bag.

Description

Technical Field

[0001] This application relates to the field of composite materials technology, and in particular to a biodegradable graphene / PBAT composite packaging bag and its preparation method. Background Technology

[0002] Polybutylene adipate / terephthalate (PBAT) is a thermoplastic biodegradable plastic formed by copolymerizing butylene adipate (PBA) and butylene terephthalate (PBT). It completely degrades within weeks under the action of naturally occurring enzymes in fertile soil. PBAT possesses both the biodegradability of aliphatic polyesters and the good mechanical properties of aromatic polyesters: good ductility, elongation at break, heat resistance, and impact resistance, while also exhibiting excellent biodegradability. It is currently one of the most actively researched and commercially successful biodegradable materials. However, PBAT suffers from poor crystallinity and low melt strength, limiting its application in the packaging bag industry. Summary of the Invention

[0003] The purpose of this invention is to solve the above-mentioned problems by providing a biodegradable graphene / PBAT composite packaging bag and its preparation method.

[0004] The technical solution of this application is implemented as follows: This invention provides a method for preparing a biodegradable graphene / PBAT composite packaging bag, comprising the following steps: S1, calcining rice husks in an air furnace to obtain rice husk ash; S2, the rice husk ash is mixed with potassium hydroxide and reacted at 700~900℃; S3. Add the product of step S2 to lime milk and react fully to precipitate calcium carbonate between the graphene. Then filter, wash until neutral, and dry to obtain calcium carbonate / graphene composite material. S4, the calcium carbonate / graphene composite material is blended with PBAT masterbatch, melt-extruded using a twin-screw extruder, and then granulated after air cooling to obtain calcium carbonate / graphene / PBAT composite masterbatch. S5, using a blown film method, a fully biodegradable graphene-based PBAT film is prepared from calcium carbonate / graphene / PBAT composite masterbatch, and then packaging bags are made.

[0005] As a further improvement, step S1 further includes: pre-treating the rice husks to remove amorphous SiO2 from the rice husks.

[0006] As a further improvement, in step S1, the rice husk is fully calcined at a temperature of 300~450℃ to form rice husk ash.

[0007] As a further improvement, in step S2, rice husk ash and potassium hydroxide are ball-milled in a ball mill at a mass ratio of 1:8~12, and then heated at 750~850°C for 1~5 hours in an inert or vacuum environment to form a graphene / potassium carbonate composite.

[0008] As a further improvement, in step S3, the lime milk is prepared by wet grinding and ultrasonic dispersion to produce lime milk with a particle size of 100~300.

[0009] As a further improvement, in step S3, the above-mentioned graphene / potassium carbonate composite is added to lime milk in stoichiometric ratio.

[0010] As a further improvement, in step S4, the calcium carbonate / graphene composite material and PBAT masterbatch are weighed and blended at a mass ratio of 1:9~15, the rotation speed is controlled at 200 rpm~400 rpm, the blending time is 10~60 minutes, and then the mixture is melt-extruded using a twin-screw extruder at an extrusion temperature of 140~170℃. After air cooling, the mixture is pelletized for later use to obtain the calcium carbonate / graphene / PBAT composite masterbatch.

[0011] The present invention further provides a biodegradable graphene / PBAT composite packaging bag, wherein the biodegradable graphene / PBAT composite packaging bag is obtained by the above-described method.

[0012] As a further improvement, the thickness of the biodegradable graphene / PBAT composite packaging bag can reach 0.03mm~0.05mm.

[0013] The present invention further provides a method for preparing a biodegradable graphene / PBAT composite material, comprising the following steps: S1, calcining rice husks in an air furnace to obtain rice husk ash; S2, the rice husk ash is mixed with potassium hydroxide and reacted at 700~900℃; S3. Add the product of step S2 to lime milk and react fully to precipitate calcium carbonate between the graphene. Then filter, wash until neutral, and dry to obtain calcium carbonate / graphene composite material. S4, the calcium carbonate / graphene composite material is blended with PBAT masterbatch, melt-extruded using a twin-screw extruder, and then pelletized after air cooling to obtain the calcium carbonate / graphene / PBAT composite material.

[0014] The advantages or beneficial effects of the above technical solutions include at least the following: Firstly, the biodegradable graphene / PBAT composite packaging bag provided by this invention significantly improves the tensile strength of PBAT by adding calcium carbonate / graphene composite material, with a maximum tensile strength of 36.7 MPa and an elongation at break of 927%. In addition, due to the excellent gas barrier properties of graphene, its two-dimensional sheet structure can effectively block the permeation of gas and water, and has good waterproof performance.

[0015] Secondly, the method for preparing the biodegradable graphene / PBAT composite packaging bag provided by this invention involves graphitizing rice husks and then precipitating them with lime milk, thereby allowing calcium carbonate to be fully precipitated and dispersed between the graphene particles. The calcium carbonate and graphene act as a barrier, preventing aggregation between graphene particles and between calcium carbonate particles, thus eliminating the need for additional dispersants and significantly improving the overall performance and degradation properties of the product. Furthermore, converting rice husks, an agricultural waste, into a high-value-added graphene / calcium carbonate composite material realizes the resource utilization of waste and reduces the environmental pollution caused by the indiscriminate disposal and incineration of agricultural waste. In addition, this invention recycles and reuses the alkaline solution generated during the reaction process, forming a closed loop of resource recycling, reducing production costs and wastewater treatment costs, and conforming to the development concept of a circular economy.

[0016] Thirdly, by optimizing the addition ratio of composite materials and the preparation process, this invention can achieve the production of PBAT packaging bags with a thickness of 0.03~0.05mm. Furthermore, due to the reduced thickness, the degradation efficiency can reach over 99%, achieving truly pollution-free production. Attached Figure Description

[0017] The accompanying drawings illustrate exemplary embodiments of the present application and, together with the description thereof, serve to explain the principles of the present application. These drawings are included to provide a further understanding of the present application and are incorporated in and constitute a part of this specification.

[0018] Figure 1 A flowchart illustrating the preparation method of the biodegradable graphene / PBAT composite packaging bag provided in an embodiment of the present invention is shown. Detailed Implementation

[0019] Embodiments of this application will now be described in more detail with reference to the accompanying drawings. While some embodiments of this application are shown in the drawings, it should be understood that this application can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this application. It should be understood that the drawings and embodiments of this application are for illustrative purposes only and are not intended to limit the scope of protection of this application.

[0020] It should be noted that, where there is no conflict, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0021] Reference Figure 1 This invention provides a method for preparing a biodegradable graphene / PBAT composite packaging bag, which includes the following steps: S1, calcining rice husks in an air furnace to obtain rice husk ash; S2, the rice husk ash is mixed with potassium hydroxide and reacted at 700~900℃; S3. Add the product of step S2 to lime milk and react fully to precipitate calcium carbonate between the graphene. Then filter, wash until neutral, and dry to obtain calcium carbonate / graphene composite material. S4, the calcium carbonate / graphene composite material is blended with PBAT masterbatch, melt-extruded using a twin-screw extruder, and then granulated after air cooling to obtain calcium carbonate / graphene / PBAT composite masterbatch. S5, using a blown film method, a fully biodegradable graphene-based PBAT film is prepared from calcium carbonate / graphene / PBAT composite masterbatch, and then packaging bags are made.

[0022] In step S1, preferably, the rice husks need to be pretreated to remove amorphous SiO2. This pretreatment primarily involves reacting the rice husks with a strong alkali to remove amorphous SiO2. Specifically, KOH reacts with the amorphous SiO2 in the rice husks to form soluble potassium silicate: 2KOH + SiO2 → K2SiO3 + H2O. Furthermore, during this process, the KOH solution can penetrate into the biomass, providing a uniform potassium source for the high-temperature reaction. Additionally, potassium hydroxide can break the hydrogen and ether bonds of cellulose / lignin, making the carbon skeleton more easily activated.

[0023] Preferably, the concentration of potassium hydroxide can be 5% to 15%. Rice husks and potassium hydroxide solution are heated to boiling at a solid-liquid ratio of 1:5 to 10 for about 0.5 to 2 hours.

[0024] After drying, the rice husks are preferably calcined at a temperature of 300-450°C to form rice husk ash, wherein the rice husk ash is mainly composed of amorphous carbon. More preferably, the calcination is carried out at a temperature of 350-400°C.

[0025] In step S2, preferably, rice husk ash and potassium hydroxide are ball-milled in a ball mill at a mass ratio of approximately 1:8 to 12, and then heated at approximately 750 to 850°C for 1 to 5 hours in an inert or vacuum environment to form a graphene / potassium carbonate composite. More preferably, rice husk ash and potassium hydroxide are ball-milled in a ball mill at a mass ratio of approximately 1:9 to 11, and the reaction temperature is controlled between 810 and 820°C.

[0026] The following reactions mainly occur in this step: 6KOH + 2C → 2K + 2K2CO3 + 3H2. In this reaction, KOH undergoes a violent redox reaction with amorphous carbon.

[0027] Gaseous potassium atoms produced at high temperatures, due to their large radius (0.23 nm) and high reactivity, can forcefully intercalate between carbon layers to form potassium intercalation compounds. Furthermore, gaseous potassium atoms are potent graphitization catalysts, lowering the energy barrier for carbon rearrangement and promoting the transformation of amorphous carbon into graphite crystals. Potassium migrates between carbon layers, guiding the ordered arrangement of six-membered carbon rings to form graphene-like structures. In addition, the H2 and O2 gases released during the reaction further expand pores and reduce oxygen-containing groups, promoting sp... 2 Carbon networks are formed.

[0028] It is understood that in other embodiments, the final graphene structure and the final proportion of K₂CO₃ can be controlled by adjusting the mass ratio of rice husk ash to potassium hydroxide, as well as the reaction temperature and time. Preferably, the mass ratio of graphene to potassium carbonate in the graphene / potassium carbonate composite is 1:25~30. Of course, the product also contains some unconverted amorphous carbon impurities. The content of each major component in the graphene / potassium carbonate composite can be obtained by dissolving potassium carbonate in water for separation and then detecting them separately.

[0029] In step S3, the lime slurry is preferably prepared into nanoscale (100~300 nm) lime slurry by wet grinding and ultrasonic dispersion, and its specific surface area is greater than or equal to 70 m². 2 / g can be inserted between graphene molecules, and can also greatly improve the reaction rate.

[0030] Specifically, the preparation of nano-lime slurry using wet grinding and ultrasonic dispersion mainly includes: Calcium hydroxide powder and deionized water are mixed in a certain ratio (mass ratio 0.1~1:10) and stirred evenly to form a preliminary lime slurry. This lime slurry is then added to a wet grinding mill. A ball mill or sand mill can be used for the wet grinding, controlling the grinding time (2-4 hours) and the particle size of the grinding media (such as zirconia beads) (0.5-1 mm). During the grinding process, samples are taken periodically to observe the particle size distribution of the lime slurry, ensuring that the particle size reaches the nanometer level (100-300 nm). The wet-ground lime slurry is then transferred to an ultrasonic disperser. The power of the ultrasonic disperser is controlled (500-1000W), and the ultrasonic treatment time is typically 30-60 minutes, adjusted according to the slurry concentration and particle size distribution.

[0031] In addition, the graphene / potassium carbonate composite was added to lime slurry in stoichiometric ratio, and the following reaction mainly occurred in this step: In the graphene / potassium carbonate composite, potassium carbonate reacts stoichiometrically with calcium hydroxide in lime slurry, producing calcium carbonate that adheres to the graphene surface or interlayer. The resulting calcium carbonate is then filtered, washed to neutral, and dried to obtain the calcium carbonate / graphene composite material. In this step, potassium carbonate is almost completely converted into calcium carbonate precipitate, and the weight ratio of calcium carbonate precipitate to graphene in the obtained calcium carbonate / graphene composite material is approximately 18~21:1.

[0032] In addition, the residual alkaline solution obtained after filtration in this step can be returned to the rice husk soaking process, or concentrated and crystallized and then returned to react with the rice husk ash at high temperature, thus forming a cycle to reduce production costs and wastewater treatment costs. In this step, some of the elemental potassium generated will also react with the aqueous solution to further generate potassium hydroxide.

[0033] In step S4, preferably, the calcium carbonate / graphene composite material and PBAT masterbatch are weighed and blended at a mass ratio of 1:9~15, the speed is controlled at 200 rpm~400 rpm, the blending time is 10~60 minutes, and then melt extrusion is performed using a twin-screw extruder, wherein the extrusion temperature is 140~170℃, and after air cooling, it is pelletized for later use to obtain calcium carbonate / graphene / PBAT composite masterbatch.

[0034] In several other embodiments, the calcium carbonate / graphene composite material and PBAT masterbatch can be weighed and blended at mass ratios of approximately 1:9, 1:10, 1:12, 1:14, and 1:15. In this case, the blending time needs to be appropriately increased as the content of the calcium carbonate / graphene composite material increases. In this invention, by changing the mass ratio of the calcium carbonate / graphene composite material to the PBAT masterbatch, the technical problems of low strength and poor weather resistance of PBAT can be effectively improved. Furthermore, as the content of the calcium carbonate / graphene composite material increases, the barrier properties of the packaging bag can be effectively increased, and the degradation cycle of the packaging bag can be reduced. However, as the content of the calcium carbonate / graphene composite material increases, it is prone to agglomeration, thus reducing processing performance.

[0035] In step S5, furthermore, a blown film machine can be used to blow a biodegradable graphene / PBAT composite packaging bag with a film thickness of 0.03mm~0.05mm.

[0036] Example 1: After cleaning the rice husks, add a 10% potassium hydroxide solution and heat to boiling for about 1 hour at a solid-liquid ratio of 1:7 to remove amorphous silica from the rice husks and reduce ash impurities. Then dry the rice husks and calcine them at 360°C to form rice husk ash (amorphous carbon). At a mass ratio of approximately 1:10, 0.5g of rice husk ash and 5.0g of potassium hydroxide were ball-milled in a ball mill. Then, under an inert or vacuum environment, the mixture was heated at approximately 815±5℃ for 1.5 hours to form a graphene / potassium carbonate composite. In this embodiment, after separation and testing, the graphene content was approximately 0.1g, the potassium carbonate content was approximately 2.76g (approximately 0.02mol), and some unconverted amorphous carbon impurities were obtained. The above product was added to lime milk according to the theoretical molar ratio and allowed to react fully, so that calcium carbonate precipitated between the graphene. Then, it was filtered, washed until neutral, and dried to obtain a calcium carbonate / graphene composite material with a calcium carbonate / graphene ratio of about 20:1. The calcium carbonate / graphene composite material and PBAT masterbatch were weighed and blended at a mass ratio of approximately 1:12. The blending speed was 350 rpm and the blending time was 20 minutes. Then, the mixture was melt-extruded using a twin-screw extruder with five temperature zones of 142℃-146℃-153℃-155℃-152℃. After air cooling, the mixture was pelletized for later use to obtain the calcium carbonate / graphene / PBAT composite masterbatch. A fully biodegradable graphene-based PBAT film with a thickness of approximately 0.05 mm is blown using a blown film machine, and then packaging bags are prepared. The size of the packaging bags can be selected according to actual needs, such as 35×45±2 (handle height 8cm).

[0037] Example 2: After cleaning the rice husks, add a 10% potassium hydroxide solution and heat to boiling for about 1 hour at a solid-liquid ratio of 1:7 to remove amorphous silica from the rice husks and reduce ash impurities. Then dry the rice husks and calcine them at 360°C to form rice husk ash (amorphous carbon). At a mass ratio of approximately 1:10, 0.5g of rice husk ash and 5.0g of potassium hydroxide were ball-milled in a ball mill. Then, under an inert or vacuum environment, the mixture was heated at approximately 815±5℃ for 1.5 hours to form a graphene / potassium carbonate composite. In this embodiment, after separation and testing, the graphene content was approximately 0.1g, the potassium carbonate content was approximately 2.76g (approximately 0.02mol), and some unconverted amorphous carbon impurities were obtained. The above product was added to lime milk according to the theoretical molar ratio and allowed to react fully, so that calcium carbonate precipitated between the graphene. Then, it was filtered, washed until neutral, and dried to obtain a calcium carbonate / graphene composite material with a calcium carbonate / graphene ratio of about 20:1. The calcium carbonate / graphene composite material and PBAT masterbatch were weighed and blended at a mass ratio of approximately 1:10. The blending speed was 350 rpm and the blending time was 35 minutes. Then, the mixture was melt-extruded using a twin-screw extruder with five temperature zones of 142℃-146℃-153℃-155℃-152℃. After air cooling, the mixture was pelletized for later use to obtain the calcium carbonate / graphene / PBAT composite masterbatch. A fully biodegradable graphene-based PBAT film with a thickness of approximately 0.05 mm was blown using a blown film machine, and then packaging bags were prepared.

[0038] Example 3: After cleaning the rice husks, add a 10% potassium hydroxide solution and heat to boiling for about 1 hour at a solid-liquid ratio of 1:7 to remove amorphous silica from the rice husks and reduce ash impurities. Then dry the rice husks and calcine them at 360°C to form rice husk ash (amorphous carbon). At a mass ratio of approximately 1:10, 0.5g of rice husk ash and 5.0g of potassium hydroxide were ball-milled in a ball mill. Then, under an inert or vacuum environment, the mixture was heated at approximately 815±5℃ for 1.5 hours to form a graphene / potassium carbonate composite. In this embodiment, after separation and testing, the graphene content was approximately 0.1g, the potassium carbonate content was approximately 2.76g (approximately 0.02mol), and some unconverted amorphous carbon impurities were obtained. The above product was added to lime milk according to the theoretical molar ratio and allowed to react fully, so that calcium carbonate precipitated between the graphene. Then, it was filtered, washed until neutral, and dried to obtain a calcium carbonate / graphene composite material with a calcium carbonate / graphene ratio of about 20:1. The calcium carbonate / graphene composite material and PBAT masterbatch were weighed and blended at a mass ratio of approximately 1:16. The blending speed was 350 rpm and the blending time was 18 minutes. Then, the mixture was melt-extruded using a twin-screw extruder with five temperature zones of 142℃-146℃-153℃-155℃-152℃. After air cooling, the mixture was pelletized for later use to obtain the calcium carbonate / graphene / PBAT composite masterbatch. A fully biodegradable graphene-based PBAT film with a thickness of approximately 0.05 mm was blown using a blown film machine, and then packaging bags were prepared.

[0039] Comparative Example 1: After cleaning the rice husks, add a 10% potassium hydroxide solution and heat to boiling for about 1 hour at a solid-liquid ratio of 1:7 to remove amorphous silica from the rice husks and reduce ash impurities. Then dry the rice husks and calcine them at 360°C to form rice husk ash (amorphous carbon). At a mass ratio of approximately 1:10, 0.5g of rice husk ash and 5.0g of potassium hydroxide were ball-milled in a ball mill. Then, under an inert or vacuum environment, the mixture was heated at approximately 815±5℃ for 1.5 hours to form a graphene / potassium carbonate composite. In this embodiment, after separation and testing, the graphene content was approximately 0.1g, the potassium carbonate content was approximately 2.76g (approximately 0.02mol), and some unconverted amorphous carbon impurities were obtained. The above product was added to lime milk according to the theoretical molar ratio and allowed to react fully, so that calcium carbonate precipitated between the graphene. Then, it was filtered, washed until neutral, and dried to obtain a calcium carbonate / graphene composite material with a calcium carbonate / graphene ratio of about 20:1. The calcium carbonate / graphene composite material and PBAT masterbatch were weighed and blended at a mass ratio of approximately 1:8. The blending speed was 350 rpm and the blending time was 60 minutes. Then, the mixture was melt-extruded using a twin-screw extruder with five temperature zones of 142℃-146℃-153℃-155℃-152℃. After air cooling, the mixture was pelletized for later use to obtain the calcium carbonate / graphene / PBAT composite masterbatch. A fully biodegradable graphene-based PBAT film with a thickness of approximately 0.1 mm was blown using a blown film machine, and then packaging bags were prepared. In this comparative example, the high content of calcium carbonate / graphene composite material reduced the overall processing performance, making it impossible to prepare fully biodegradable graphene-based PBAT films and packaging bags with a thickness of less than 0.1 mm.

[0040] Test example: Standard specimens were obtained by injection molding of the calcium carbonate / graphene / PBAT composite masterbatch prepared in Examples 1-3 and Comparative Example 1 of this patent application. The tensile properties were tested. The tensile property test standard was the national standard GB / T1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molding and extruding plastics". The test results are shown in Table 1.

[0041] Table 1 shows the tensile property tests of the examples and comparative examples.

[0042] As shown in Table 1, the tensile strength of the calcium carbonate / graphene composite material increases with increasing content. However, when the ratio of the calcium carbonate / graphene composite material to PBAT masterbatch reaches approximately 1:8, the overall tensile strength decreases, possibly due to uneven dispersion. This is because graphene possesses excellent mechanical properties, and its addition can improve the tensile strength and elongation at break of PBAT.

[0043] The performance of the packaging bags prepared in Examples 1-3 and Comparative Example 1 of this patent application was tested. The performance test standard was the national standard GB / T 38082—2019 "Biodegradable Plastic Shopping Bags". The test results are shown in Table 2.

[0044] Table 2 shows the performance tests for the examples and comparative examples.

[0045] Based on the data above, since the thickness of the packaging bag in Comparative Example 1 is 0.1 mm, it is not comparable to the data in the Examples (thickness 0.05 mm). However, based on the data from Examples 1-3, the degradation efficiency of the packaging bag with a thickness of 0.05 mm can reach over 99%, and the degradation rate significantly increases with the content of calcium carbonate / graphene composite material. This may be because, on the one hand, in the soil environment, calcium carbonate can react with carbon dioxide and water to form soluble calcium bicarbonate, thereby forming micropores on the PBAT film, increasing the contact area between the film and microorganisms, and promoting their degradation. Furthermore, graphene has excellent gas and liquid barrier properties, and its addition can effectively reduce the oxygen and water vapor permeability of the PBAT packaging bag.

[0046] Those skilled in the art should understand that the above embodiments are merely for illustrative purposes and are not intended to limit the scope of this application. Those skilled in the art can make other changes or modifications based on the above disclosure, and these changes or modifications still fall within the scope of this application.

Claims

1. A method for preparing a biodegradable graphene / PBAT composite packaging bag, characterized in that: Includes the following steps: S1, calcining rice husks in an air furnace to obtain rice husk ash; S2, the rice husk ash is mixed with potassium hydroxide and reacted at 700~900℃. By adjusting the mass ratio of rice husk ash to potassium hydroxide, as well as the reaction temperature and time, the final graphene structure and the final proportion of K2CO3 are controlled. S3. Add the product of step S2 to lime milk and react fully to precipitate calcium carbonate between the graphene. Then filter, wash until neutral, and dry to obtain calcium carbonate / graphene composite material. S4, the calcium carbonate / graphene composite material is blended with PBAT masterbatch, melt-extruded using a twin-screw extruder, and then granulated after air cooling to obtain calcium carbonate / graphene / PBAT composite masterbatch. S5, using a blown film method, a fully biodegradable graphene-based PBAT film is prepared from calcium carbonate / graphene / PBAT composite masterbatch, and then packaging bags are made.

2. The method for preparing the biodegradable graphene / PBAT composite packaging bag according to claim 1, characterized in that: Step S1 further includes: pre-treating the rice husks to remove amorphous SiO2 from the rice husks.

3. The method for preparing the biodegradable graphene / PBAT composite packaging bag according to claim 1, characterized in that: In step S1, the rice husk ash is fully calcined at a temperature of 300~450℃ to form rice husk ash.

4. The method for preparing the biodegradable graphene / PBAT composite packaging bag according to claim 1, characterized in that: In step S2, rice husk ash and potassium hydroxide are ball-milled in a ball mill at a mass ratio of 1:8~12. Then, the mixture is heated at 750~850℃ for 1~5 hours in an inert or vacuum environment to form a graphene / potassium carbonate composite.

5. The method for preparing the biodegradable graphene / PBAT composite packaging bag according to claim 1, characterized in that: In step S3, the lime milk is prepared by wet grinding and ultrasonic dispersion to produce lime milk with a particle size of 100~300 nanometers.

6. The method for preparing the biodegradable graphene / PBAT composite packaging bag according to claim 1, characterized in that: In step S3, the graphene / potassium carbonate composite is added to lime milk in stoichiometric ratio.

7. The method for preparing the biodegradable graphene / PBAT composite packaging bag according to claim 1, characterized in that: In step S4, the calcium carbonate / graphene composite material and PBAT masterbatch are weighed and blended at a mass ratio of 1:9~15, the rotation speed is controlled at 200 rpm~400 rpm, the blending time is 10~60 minutes, and then the mixture is melt-extruded using a twin-screw extruder at an extrusion temperature of 140~170℃. After air cooling, the mixture is pelletized for later use to obtain the calcium carbonate / graphene / PBAT composite masterbatch.

8. A biodegradable graphene / PBAT composite packaging bag, characterized in that: The biodegradable graphene / PBAT composite packaging bag is obtained by the method described in claims 1-7.

9. The biodegradable graphene / PBAT composite packaging bag as described in claim 8, characterized in that: The thickness of the biodegradable graphene / PBAT composite packaging bag is 0.03mm~0.05mm.

10. A method for preparing a biodegradable graphene / PBAT composite material, characterized in that: Includes the following steps: S1, calcining rice husks in an air furnace to obtain rice husk ash; S2, the rice husk ash is mixed with potassium hydroxide and reacted at 700~900℃; S3. Add the product of step S2 to lime milk and react fully to precipitate calcium carbonate between the graphene. Then filter, wash until neutral, and dry to obtain calcium carbonate / graphene composite material. S4, the calcium carbonate / graphene composite material is blended with PBAT masterbatch, melt-extruded using a twin-screw extruder, and then pelletized after air cooling to obtain the calcium carbonate / graphene / PBAT composite material.

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