Thermoplastic starch foaming meal box and preparation method thereof

Abstract

The invention belongs to the related technical field of degradable foaming tableware, and particularly relates to a thermoplastic starch foaming meal box and a preparation method thereof. The thermoplastic starch foaming meal box is prepared from the following raw materials in parts by weight: 30-45 parts of a starch-based foaming material, 10-22 parts of a bioactive compound, 6-12 parts of a foaming agent, 3-6 parts of calcium carbonate, 10-15 parts of polyethylene, 2-8 parts of glycerol, 5-10 parts of organic clay and 25-35 parts of a natural polymer, the starch-based foaming material is prepared by blending plant starch and plant fibers; according to the invention, the plant starch and the plant fibers are blended, so that the prepared lunch box can form a three-dimensional network skeleton structure during foaming, and the foaming lunch box is prevented from generating gaps; a bioactive compound is adopted, so that the prepared foaming meal box is good in compression resistance; a microwave foaming mode is adopted to replace a traditional extrusion foaming mode, so that the prepared meal box can resist the temperature of 80 DEG C.

Description

Technical Field

[0001] The invention belongs to the technical field related to degradable foamed tableware, and in particular relates to a thermoplastic starch foamed lunch box and a preparation method thereof. Background Art

[0002] Foam tableware, that is, disposable foam plastic tableware, refers to polystyrene resin as raw material, which is heated and melted in an extruder at high temperature and then extruded into sheets by adding a foaming agent. After the sheets are rolled up, they are placed in a ventilated and humid environment for health care and then heated again for suction molding to make various tableware such as fast food boxes, soup bowls, instant noodle bowls, fresh food trays, etc.

[0003] Traditional foam tableware often uses petroleum and plastic. The raw materials of petroleum-based plastics mainly come from petrochemical products, which are non-renewable and difficult to degrade in the environment. Long-term use will cause serious "white pollution".

[0004] Nowadays, starch-based foaming materials that are more easily degradable can be used to replace petroleum-based plastics, but the existing starch-based foaming materials still have many shortcomings: First, the foam structure of starch-based foaming materials is uneven and has a low expansion rate, resulting in overall mechanical properties that are inferior to those of petroleum-based plastics. The overall strength and toughness of the lunch boxes or tableware made from them are far inferior to those made from petroleum-based plastics. They are prone to aging and becoming brittle. When the tableware is squeezed, it is easy to break, affecting the user experience. Secondly, starch-based foaming materials themselves do not have sufficient antibacterial properties. When used on lunch boxes, they cannot effectively inhibit the growth of microorganisms in food, thus affecting the shelf life and safety of food. Finally, the lunch boxes made of existing starch-based foam materials have poor overall thermal insulation effects and insufficient heat resistance. Most of them can only withstand heat of around 60°C, which affects the user experience and physical health. Summary of the invention

[0005] In order to overcome the deficiencies of the prior art, the present invention provides a thermoplastic starch foaming lunch box and a preparation method thereof.

[0006] The present invention adopts a blend of plant starch and plant fiber, so that the prepared lunch box can form a "three-dimensional network" skeleton structure during foaming, thereby preventing the foamed lunch box from having gaps; the use of bioactive compounds makes the prepared foamed lunch box have good pressure resistance; the invention adopts microwave foaming instead of traditional extrusion foaming, so that the prepared lunch box can withstand a temperature of 80°C.

[0007] In order to achieve the above-mentioned object, the present invention provides the following technical scheme: a thermoplastic starch foam lunch box, wherein the raw materials for preparing the thermoplastic starch foam lunch box include, by weight: 30-45 parts of starch-based foaming material, 10-22 parts of bioactive compound, 6-12 parts of foaming agent, 3-6 parts of calcium carbonate, 10-15 parts of polyethylene, 2-8 parts of glycerol, 5-10 parts of organic clay and 25-35 parts of natural polymer; The starch-based foaming material is prepared by blending plant starch and plant fiber; Wherein, the starch-based foaming material is blended by 30-45 parts of plant starch and 25-35 parts of plant fiber by weight.

[0008] Through the combined use of plant fiber and plant starch, while ensuring that the lunch box can be smoothly degraded without harm, the plant fiber itself has a certain toughness and support properties. Just like steel bars in construction, it can build a stable "three-dimensional network" skeleton structure for the lunch box during the foaming process. The plant starch uses its own viscosity to fill the skeleton, playing a role of bonding and auxiliary stability, so that the lunch box will not have structural defects during the foaming process, which helps to improve the quality and practicality of the lunch box.

[0009] In the above-mentioned thermoplastic starch foam lunch box, the raw materials for preparing the bioactive compound include, by weight: 5-10 parts of rice husks, 22-28 parts of banana leaves, 5-8 parts of peanut skins, 3-6 parts of plantain husks, 15-23 parts of grape stems and 8-16 parts of sugarcane bagasse.

[0010] The above materials are selected on the one hand because the raw materials are widely available and relatively low in cost, most of which are agricultural waste. On the other hand, rice husks, peanut skins, grape stems, etc. contain cellulose, hemicellulose, etc., while banana leaves, etc. contain polyphenols. Mixing them can obtain compounds with multiple biological activities, which can effectively improve the molding quality and molding effect of the lunch box.

[0011] In the above-mentioned thermoplastic starch foaming lunch box, the raw materials for preparing the foaming agent include, by weight: 30-45 parts of pure water, 2-8 parts of ethanol, 4-6 parts of sodium bicarbonate, 1-3 parts of citric acid and 8-16 parts of stearate. Through the arrangement of the above-mentioned materials, the bubble wall produced during foaming has higher hardness and strength, making the foam more delicate and stable while the foaming amount is effectively improved, and the generation of irritating gas can be avoided, so that the lunch box will not have excessive odor, and the user experience is guaranteed.

[0012] In the above-mentioned thermoplastic starch foamed lunch box, the plant starch is one of sweet potato starch, corn starch, potato starch and cassava starch. After plastic treatment, thermoplasticity can be obtained, so that it can be melted and formed at high temperature, and maintain a stable shape after cooling.

[0013] In the above-mentioned thermoplastic starch foamed lunch box, the plant fiber is one of poplar fiber, cedar fiber, privet fiber, cotton fiber, jute fiber, flax fiber, bamboo fiber and coconut fiber. The above-mentioned fibers can improve the overall mechanical properties of the lunch box, and also make the lunch box customized according to customer needs. For example, when the poplar fiber is evenly dispersed in the thermoplastic starch, the lunch box is not easy to deform when subjected to a certain pressure such as stacking or extrusion during transportation, and maintains its original shape. The application of cedar fiber in the thermoplastic starch foamed lunch box can reduce bacterial growth in a short time and maintain the freshness of food.

[0014] In the above-mentioned thermoplastic starch foam lunch box, the natural polymer is one of cellulose, chitosan and protein. By setting the natural polymer, the stability of the lunch box after molding can be improved while ensuring good degradability.

[0015] A method for preparing a thermoplastic starch foamed lunch box comprises the following steps: S1: preparing a starch-based foaming material: mixing plant starch and plant fiber to obtain a starch-based foaming material; S2: Preparation of biologically active compounds: S2.1: Crush rice husks, banana leaves, peanut skins, plantain skins, grape stems and sugarcane bagasse, mix them and evenly divide them into two parts, put one part into a container and add ethanol solution to cover the crushed materials, soak them for later use; S2.2: Place the other portion in a dry and cool place to air-dry for 3-5 days, then add it to the container and continue soaking for 12-15 days, then take it out to obtain the bioactive compound; By crushing the raw materials, the contact area between the raw materials and the solvent can be increased, which is beneficial to the subsequent extraction of active compounds. By air-drying the other part and then soaking it, the prepared lunch box can also have antioxidant and antibacterial properties.

[0016] S3: preparing a foaming agent: mixing pure water, ethanol, sodium bicarbonate, citric acid and stearate to obtain a foaming agent; S4: preparing thermoplastic starch foamed lunch box; S4.1: Mixing a starch-based foaming material, a bioactive compound, a foaming agent, calcium carbonate, polyethylene, glycerol, an organoclay and a natural polymer to obtain a blended material; S4.2: heating the blended material in a 700-900 watt microwave environment for 40-60 minutes to obtain a preformed material; S4.3: The prefabricated material is squeezed into a mold, heated to 120-145° C. for 2-5 minutes, and then water-cooled to obtain a thermoplastic starch foamed lunch box.

[0017] Through microwave foaming technology, on the one hand, the heating rate can be guaranteed, so that the heating uniformity is improved, while the production process can be simplified, the processing steps can be reduced, and the production efficiency can be improved. On the other hand, the controllability is better than extrusion foaming, which can effectively ensure the stability of the foam and improve the molding quality of the lunch box.

[0018] In the above-mentioned method for preparing the thermoplastic starch foam lunch box, the starch-based foam material in S1 needs to be placed in a 60°C stirrer during preparation, set at 60-120 r / min and stirred for 10-15 minutes, and then stored at a constant temperature of 60°C.

[0019] By mixing plant starch and plant fiber, placing them in a 60°C agitator, stirring at 60-120 r / min for 10-15 minutes, and storing them at a constant temperature of 60°C, a starch-based foaming material with good mechanical properties, moisture resistance, thermodynamic properties, hydrophobic properties and degradability can be obtained.

[0020] In the above-mentioned method for preparing the thermoplastic starch foamed lunch box, the foaming agent in S3 needs to be placed in a centrifugal stirrer at 300-350 r / min for 45-60 min.

[0021] In the above-mentioned method for preparing the thermoplastic starch foam lunch box, the ethanol solution in S2.1 has an ethanol content of 25%. The ethanol solution concentration of 25% can ensure a certain solubility, is relatively safe and has a low cost.

[0022] In summary, compared with the prior art, the beneficial effects of this solution are: 1. The present invention adopts the technical design of blending conventional plant starch with a variety of plant fibers, so that the prepared lunch box can form a "three-dimensional network" skeleton structure by utilizing the characteristics of both during the foaming process, thereby improving the overall structure and mechanical properties of the lunch box, while preventing the foamed lunch box from having gaps, and allowing the lunch box to be slightly adjusted and customized according to customer needs, thereby improving the overall user experience.

[0023] 2. The technical design of the present invention uses bioactive compounds made from agricultural waste, which, on the one hand, effectively improves the overall compressive resistance and strength of the prepared foam lunch box, and on the other hand, can also reduce the overall cost of the lunch box, making it easier to promote and use the lunch box.

[0024] 3. The present invention adopts microwave foaming to replace the traditional extrusion foaming technology. On the one hand, it can ensure the heating rate, improve the heating uniformity, and simplify the production process, reduce the processing steps, and improve the production efficiency. On the other hand, the controllability is better than the extrusion foaming, which can effectively ensure the stability of the foam and improve the molding quality of the lunch box. The prepared lunch box can withstand a temperature of 80°C, which effectively increases the application range of the lunch box and has a good promotion effect. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely.

[0026] A thermoplastic starch foam lunch box and preparation method thereof: Embodiment 1: Step 1, preparing a starch-based foaming material: mixing 30 parts of sweet potato starch and 25 parts of cedar wood fibers, placing in a 60°C agitator, setting 60 r / min, stirring for 10 minutes, and keeping at a constant temperature of 60°C to obtain a starch-based foaming material; Step 2, preparing bioactive compounds: (i) 5 parts of rice husks, 22 parts of banana leaves, 5 parts of peanut skins, 3 parts of plantain skins, 15 parts of grape stems and 8 parts of sugarcane bagasse are crushed, mixed and evenly divided into two parts, one of which is put into a container, and a 25% ethanol solution is added to cover the crushed materials, and soaked for later use; (ii) the other part is placed in a dry and cool place to air-dry for 3 days, then added to the container, and soaked for 12 days, and taken out to obtain the bioactive compound; Step 3, preparing a foaming agent: 30 parts of pure water, 2 parts of ethanol, 4 parts of sodium bicarbonate, 1 part of citric acid and 8 parts of stearate are mixed, placed in a centrifugal stirrer, and stirred at 300 r / min for 45 minutes to obtain a foaming agent; Step 4. Prepare a thermoplastic starch foam lunch box: (i) Mix 30 parts of starch-based foaming material, 10 parts of bioactive compounds, 6 parts of foaming agents, 3 parts of calcium carbonate, 10 parts of polyethylene, 2 parts of glycerol, 5 parts of organic clay and 25 parts of cellulose to obtain a blended material; (ii) Heat the blended material in a 700-watt microwave environment for 40 minutes to obtain a prefabricated material; (iii) Extrude the prefabricated material into a mold, heat to 120°C for 2 minutes, and then water-cool it to obtain a thermoplastic starch foamed lunch box.

[0027] Embodiment 2: Step 1, preparing a starch-based foaming material: 37 parts of potato starch and 30 parts of poplar wood fiber were mixed, placed in a 60°C agitator, set at 85 r / min, stirred for 12 minutes, and kept at a constant temperature of 60°C to obtain a starch-based foaming material; Step 2, preparing bioactive compounds: (i) 8 parts of rice husks, 24 parts of banana leaves, 6 parts of peanut skins, 5 parts of plantain skins, 19 parts of grape stems and 13 parts of sugarcane bagasse are crushed, mixed and evenly divided into two parts, one of which is put into a container, and a 25% ethanol solution is added to cover the crushed materials, and soaked for later use; (ii) the other part is placed in a dry and cool place to air-dry for 4 days, then added to the container, and soaked for 13 days, and then taken out to obtain the bioactive compound; Step 3, preparing a foaming agent: 38 parts of pure water, 6 parts of ethanol, 5 parts of sodium bicarbonate, 2 parts of citric acid and 12 parts of stearate are mixed, placed in a centrifugal stirrer, and stirred at 320 r / min for 55 min to obtain a foaming agent; Step 4. Prepare a thermoplastic starch foam lunch box: (i) Mix 37 parts of starch-based foaming material, 16 parts of bioactive compounds, 8 parts of foaming agents, 4 parts of calcium carbonate, 12 parts of polyethylene, 6 parts of glycerol, 8 parts of organic clay and 30 parts of cellulose to obtain a blended material; (ii) Heat the blended material in an 800-watt microwave environment for 50 minutes to obtain a prefabricated material; (iii) Extrude the prefabricated material into a mold, heat to 130°C for 4 minutes, and then water-cool it to obtain a thermoplastic starch foamed lunch box.

[0028] Embodiment 3: Step 1, preparing a starch-based foaming material: 45 parts of corn starch and 35 parts of poplar wood fiber were mixed, placed in a 60°C agitator, set at 120 r / min, stirred for 15 minutes, and kept at a constant temperature of 60°C to obtain a starch-based foaming material; Step 2, preparing bioactive compounds: (i) crush 10 parts of rice husks, 28 parts of banana leaves, 8 parts of peanut skins, 6 parts of plantain skins, 23 parts of grape stems and 16 parts of sugarcane bagasse, mix them and evenly divide them into two parts, one of which is put into a container, and 25% ethanol solution is added to cover the crushed materials, and soaked for later use; (ii) the other part is placed in a dry and cool place to air-dry for 5 days, then added to the container, and soaked for 15 days, and then taken out to obtain the bioactive compound; Step 3, preparing a foaming agent: 45 parts of pure water, 8 parts of ethanol, 6 parts of sodium bicarbonate, 3 parts of citric acid and 16 parts of stearate are mixed, placed in a centrifugal stirrer, and stirred at 350 r / min for 60 min to obtain a foaming agent; Step 4. Prepare a thermoplastic starch foam lunch box: (i) Mix 45 parts of starch-based foaming material, 22 parts of bioactive compounds, 12 parts of foaming agents, 6 parts of calcium carbonate, 15 parts of polyethylene, 8 parts of glycerol, 10 parts of organic clay and 35 parts of cellulose to obtain a blended material; (ii) Heat the blended material in a 900-watt microwave environment for 60 minutes to obtain a prefabricated material; (iii) Extrude the prefabricated material into a mold, heat to 145°C for 5 minutes, and then water-cool it to obtain a thermoplastic starch foamed lunch box.

[0029] Comparative Example 1 (without using plant fiber) Step 1, preparing a starch-based foaming material: placing 37 parts of corn starch in a 60°C agitator, setting the temperature to 85 r / min, stirring for 12 minutes, and storing at a constant temperature of 60°C to obtain a starch-based foaming material; Step 2, preparing bioactive compounds: (i) 8 parts of rice husks, 24 parts of banana leaves, 6 parts of peanut skins, 5 parts of plantain skins, 19 parts of grape stems and 13 parts of sugarcane bagasse are crushed, mixed and evenly divided into two parts, one of which is put into a container and a 25% ethanol solution is added to cover the crushed materials, and soaked for later use; (ii) the other part is placed in a dry and cool place to air-dry for 4 days, then added to the container, and soaked for 13 days, and then taken out to obtain the bioactive compound; Step 3, preparing a foaming agent: 38 parts of pure water, 6 parts of ethanol, 5 parts of sodium bicarbonate, 2 parts of citric acid and 12 parts of stearate are mixed, placed in a centrifugal stirrer, and stirred at 320 r / min for 55 min to obtain a foaming agent; Step 4. Prepare a thermoplastic starch foam lunch box: (i) Mix 37 parts of starch-based foaming material, 16 parts of bioactive compounds, 8 parts of foaming agents, 4 parts of calcium carbonate, 12 parts of polyethylene, 6 parts of glycerol, 8 parts of organic clay and 30 parts of cellulose to obtain a blended material; (ii) Heat the blended material in an 800-watt microwave environment for 50 minutes to obtain a prefabricated material; (iii) Extrude the prefabricated material into a mold, heat to 130°C for 4 minutes, and then water-cool it to obtain a thermoplastic starch foamed lunch box.

[0030] Comparative Example 2 (No preparation of biologically active compounds) Step 1, preparing a starch-based foaming material: 37 parts of corn starch and 30 parts of poplar wood fiber were mixed, placed in a 60°C agitator, set at 85 r / min, stirred for 12 minutes, and kept at a constant temperature of 60°C to obtain a starch-based foaming material; Step 2, preparing a foaming agent: 38 parts of pure water, 6 parts of ethanol, 5 parts of sodium bicarbonate, 2 parts of citric acid and 12 parts of stearate are mixed, placed in a centrifugal stirrer, and stirred at 320 r / min for 55 min to obtain a foaming agent; Step 3. Prepare a thermoplastic starch foam lunch box: (i) Mix 37 parts of starch-based foaming material, 8 parts of foaming agent, 4 parts of calcium carbonate, 12 parts of polyethylene, 6 parts of glycerol, 8 parts of organic clay and 46 parts of cellulose to obtain a blended material; (ii) Heat the blended material in an 800-watt microwave environment for 50 minutes to obtain a prefabricated material; (iii) Extrude the prefabricated material into a mold, heat to 130°C for 4 minutes, and then water-cool it to obtain a thermoplastic starch foamed lunch box.

[0031] Comparative Example 3 (Microwave foaming changed to extrusion foaming) Step 1, preparing a starch-based foaming material: 37 parts of corn starch and 30 parts of poplar wood fiber are mixed, placed in a 60°C agitator, stirred at 85 r / min for 12 minutes, and stored at a constant temperature of 60°C to obtain a starch-based foaming material; Step 2, preparing bioactive compounds: (i) 8 parts of rice husks, 24 parts of banana leaves, 6 parts of peanut skins, 5 parts of plantain skins, 19 parts of grape stems and 13 parts of sugarcane bagasse are crushed, mixed and evenly divided into two parts, one of which is put into a container and a 25% ethanol solution is added to cover the crushed materials, and soaked for later use; (ii) the other part is placed in a dry and cool place to air-dry for 4 days, then added to the container, and soaked for 13 days, and then taken out to obtain the bioactive compound; Step 3, preparing a foaming agent: 38 parts of pure water, 6 parts of ethanol, 5 parts of sodium bicarbonate, 2 parts of citric acid and 12 parts of stearate are mixed, placed in a centrifugal stirrer, and stirred at 320 r / min for 55 min to obtain a foaming agent; Step 4. Prepare a thermoplastic starch foam lunch box: (i) Mix 37 parts of starch-based foaming material, 16 parts of bioactive compounds, 8 parts of foaming agents, 4 parts of calcium carbonate, 12 parts of polyethylene, 6 parts of glycerol, 8 parts of organic clay and 30 parts of cellulose to obtain a blended material; (ii) The blended material is subjected to a two-step molding process, i.e., granulation by a twin-screw extruder at 60°C, and then single-screw extrusion foaming at 80°C after cooling to obtain a prefabricated material; (iii) The prefabricated material is extruded into a mold, heated to 130°C for 4 minutes, and then water-cooled to obtain a thermoplastic starch foamed lunch box.

[0032] Experimental data: According to GB 4806.7-2023 "National Food Safety Standard for Plastic Materials and Products for Food Contact", the performance of the foam lunch boxes prepared by the methods of Examples 1-3 and Comparative Examples 1-3 was tested: Table 1

[0033] As can be seen from Table 1, the foam lunch boxes prepared by the methods of Examples 1-3 are superior to the foam lunch boxes prepared by the methods of Comparative Examples 1-3 in all aspects of performance; First, by comparing Examples 1-3, the compressive strength of the foam is increased from 650 kPa in Example 1 to 820 kPa in Example 2, and the mechanical properties of the foam obtained are the best. At the same time, it can be seen that the foam lunch box prepared by the method of Example 2 is better than the foam lunch boxes prepared by the methods of Examples 1 and 3 in terms of high temperature resistance, compressive strength and hygienic index performance, which can effectively guarantee the experience in actual use; Comparing Comparative Example 1 with Examples 1-3, it can be seen that the difference between Examples 1-3 and Comparative Example 1 is that no plant starch and plant fiber are blended, resulting in the prepared lunch box not forming a "three-dimensional network" skeleton structure during foaming, resulting in a decrease in the overall temperature resistance and compressive strength, and notches are formed on the surface of the formed lunch box, which seriously affects the user experience; Comparing Comparative Example 2 with Examples 1-3, it can be seen that the difference between Examples 1-3 and Comparative Example 2 is that no bioactive compound is used, which results in a significant decline in the compressive strength of the prepared lunch box. At the same time, the overall thickness of the lunch box is uneven. If there is external pressure squeezing or bumping during actual use, it is very easy to be damaged, causing the food inside to fall off; Comparing Comparative Example 3 with Example 2, it can be seen that when all data are the same as those of other comparative examples, when only double-screw extrusion is used for molding, the temperature resistance of the overall lunch box will be significantly reduced, and only food within 58°C can be placed in it, which seriously affects the promotion and use scope of the lunch box and greatly reduces the use effect of the lunch box.

[0034] For example, certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different terms to refer to the same component. This specification and claims do not use differences in names as a way to distinguish components, but use differences in the functions of components as the criteria for distinction. For example, "including" mentioned throughout the specification and claims is an open term, so it should be interpreted as "including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve the technical problem within a certain error range and basically achieve the technical effect.

[0035] It should be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a product or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such product or system. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the product or system including the elements.

[0036] The above description shows and describes several preferred embodiments of the present application, but as mentioned above, it should be understood that the present application is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the application concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not deviate from the spirit and scope of the present application, and should be within the scope of protection of the claims attached to the present application.

Claims

1. A thermoplastic starch foam lunch box, characterized in that: The raw materials for preparing the thermoplastic starch foam lunch box include, by weight: 30-45 parts of starch-based foaming material, 10-22 parts of bioactive compound, 6-12 parts of foaming agent, 3-6 parts of calcium carbonate, 10-15 parts of polyethylene, 2-8 parts of glycerol, 5-10 parts of organic clay and 25-35 parts of natural polymer; The starch-based foaming material is prepared by blending plant starch and plant fiber; Wherein, the starch-based foaming material is blended by 30-45 parts of plant starch and 25-35 parts of plant fiber by weight.

2. A thermoplastic starch foam lunch box according to claim 1, characterized in that: By weight, the raw materials for preparing the bioactive compound include: 5-10 parts of rice husks, 22-28 parts of banana leaves, 5-8 parts of peanut skins, 3-6 parts of plantain skins, 15-23 parts of grape stems and 8-16 parts of sugarcane bagasse.

3. A thermoplastic starch foam lunch box according to claim 1, characterized in that: The raw materials for preparing the foaming agent include, by weight: 30-45 parts of pure water, 2-8 parts of ethanol, 4-6 parts of sodium bicarbonate, 1-3 parts of citric acid and 8-16 parts of stearate.

4. A thermoplastic starch foam lunch box according to claim 1, characterized in that: The plant starch is one of sweet potato starch, corn starch, potato starch and cassava starch.

5. The thermoplastic starch foam lunch box according to claim 1, characterized in that: The plant fiber is one of poplar fiber, cedar fiber, privet fiber, cotton fiber, jute fiber, flax fiber, bamboo fiber and coconut fiber.

6. A thermoplastic starch foam lunch box according to claim 1, characterized in that: The natural polymer is one of cellulose, chitosan and protein.

7. A method for preparing a thermoplastic starch foam lunch box, characterized in that: The following steps are involved: S1: preparing a starch-based foaming material: mixing plant starch and plant fiber to obtain a starch-based foaming material; S2: Preparation of biologically active compounds: S2.1: Crush rice husks, banana leaves, peanut skins, plantain skins, grape stems and sugarcane bagasse, mix them and evenly divide them into two parts, put one part into a container and add ethanol solution to cover the crushed materials, soak them for later use; S2.2: Place the other portion in a dry and cool place to air-dry for 3-5 days, then add it to the container and continue soaking for 12-15 days, then take it out to obtain the bioactive compound; S3: preparing a foaming agent: mixing pure water, ethanol, sodium bicarbonate, citric acid and stearate to obtain a foaming agent; S4: preparing thermoplastic starch foamed lunch box; S4.1: Mixing a starch-based foaming material, a bioactive compound, a foaming agent, calcium carbonate, polyethylene, glycerol, an organoclay and a natural polymer to obtain a blended material; S4.2: heating the blended material in a 700-900 watt microwave environment for 40-60 minutes to obtain a preformed material; S4.3: The prefabricated material is squeezed into a mold, heated to 120-145° C. for 2-5 minutes, and then water-cooled to obtain a thermoplastic starch foamed lunch box.

8. The method for preparing a thermoplastic starch foamed lunch box according to claim 7, characterized in that: When preparing the starch-based foaming material in S1, it needs to be placed in a 60°C agitator, stirred at 60-120 r / min for 10-15 minutes, and then stored at a constant temperature of 60°C.

9. The method for preparing a thermoplastic starch foamed lunch box according to claim 7, characterized in that: When preparing the foaming agent in S3, it needs to be placed in a centrifugal stirrer at 300-350 r / min and stirred for 45-60 min.

10. The method for preparing a thermoplastic starch foamed lunch box according to claim 7, characterized in that: The ethanol solution in S2.1 has an ethanol content of 25%.

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