An epoxy-modified starch-based biodegradable membrane and its preparation method

Abstract

This invention relates to the field of membrane materials and discloses an epoxy-modified starch-based biodegradable membrane and its preparation method. The epoxy-modified starch-based biodegradable membrane comprises: epoxidized starch, modified nanocellulose, and a plasticizer. The modified nanocellulose is prepared by mixing a modified composite filler, a nanocellulose dispersion, and an aqueous solution of zinc acetate dihydrate. The nanocellulose dispersion is prepared by oxidizing and self-polymerizing tannic acid to form polytannic acid, which adheres to the surface of the nanocellulose. The modified composite filler is prepared by carboxylating fumed silica nanoparticles coated with nano-titanium dioxide with succinic anhydride and γ-aminopropyltriethoxysilane, followed by reaction with polyethyleneimine to obtain an aminated composite filler. Finally, epoxypropyldodecyl dimethylammonium chloride is grafted onto the surface of the aminated composite filler. The membrane material prepared by this invention has high tensile strength, certain hydrophobicity, and good heat resistance, antibacterial properties, and flame retardant properties.

Description

Technical Field

[0001] This invention belongs to the field of membrane material technology, specifically relating to an epoxy-modified starch-based biodegradable membrane and its preparation method. Background Technology

[0002] The scarcity of petroleum resources has led to the gradual replacement of traditional plastics by natural polymers. Among them, starch is widely used in food packaging due to its excellent film-forming ability and its low cost and easy availability. As a natural polymer compound, starch has a granular and microcrystalline structure, is widely distributed in nature, has abundant reserves, a short regeneration cycle, low price, and is biodegradable, making it a rather ideal renewable and environmentally friendly resource. However, pure starch-based film materials usually have a heterogeneous microstructure, resulting in high brittleness and unsatisfactory water-blocking and mechanical properties. Therefore, inorganic fillers are usually added to the starch matrix to improve the mechanical and barrier properties of starch-based film materials. However, inorganic fillers have the defects of easy agglomeration and poor compatibility with polymer matrices, making it difficult to disperse evenly in starch-based film materials, thus affecting the application range of starch-based film materials.

[0003] In addition, existing starch-based film materials are generally flammable. Chinese patent application number CN201410777429.1 discloses a biodegradable flame-retardant plastic film and its preparation method. The raw material components contain 25-30 parts of nano flame-retardant composite agent, which is mainly composed of silicohydroxyapatite, red phosphorus, attapulgite, hydrotalcite, montmorillonite, titanium dioxide, calcite, kaolin, etc. However, the addition of a large amount of nano flame-retardant composite agent will inevitably affect the mechanical properties of starch-based film materials. Moreover, existing starch-based film materials have problems such as poor hydrophobicity, lack of antibacterial properties and insufficient UV resistance, which seriously limits their widespread application.

[0004] Existing technologies use nano-titanium dioxide to enhance UV resistance and antibacterial properties. However, since the antibacterial activity of nano-titanium dioxide mainly depends on photocatalysis, its antibacterial effect is poor under low light or dark conditions. Natural organic antibacterial materials come from nature and have advantages such as strong antibacterial activity, safety and environmental friendliness, and low likelihood of bacteria developing drug resistance. However, they are prone to migration and loss from the matrix, resulting in poor antibacterial stability and short duration of antibacterial action, which greatly limits their development in practical applications. Summary of the Invention

[0005] To address the shortcomings mentioned in the background art, the present invention aims to provide an epoxy-modified starch-based biodegradable membrane and its preparation method. By adding modified nanocellulose, the prepared membrane material has high tensile strength, certain hydrophobicity, and good heat resistance, antibacterial properties, and flame retardant properties.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] An epoxy-modified starch-based biodegradable film comprises the following components in parts by weight: 50-70 parts of epoxidized starch, 5-15 parts of modified nanocellulose, and 15-25 parts of plasticizer;

[0008] The modified nanocellulose is prepared by mixing modified composite filler, nanocellulose dispersion, and zinc acetate dihydrate aqueous solution in an aqueous phase through ion exchange and acid-base neutralization reaction; wherein the nanocellulose dispersion is prepared by tannic acid oxidation self-polymerization to form polytannic acid that adheres to the surface of nanocellulose.

[0009] The modified composite filler is prepared by carboxylating fumed silica nanoparticles coated with nano-titanium dioxide using succinic anhydride and γ-aminopropyltriethoxysilane, followed by an amidation reaction with polyethyleneimine to obtain an aminated composite filler, and finally quaternization modification by chemically grafting glycidyl dodecyl dimethyl ammonium chloride onto the surface of the aminated composite filler using a ring-opening reaction.

[0010] Preferably, the preparation method of the epoxidized starch includes the following steps: taking dry starch in a reactor, adding ethyl acetate, epichlorohydrin and pyridine, stirring and reacting at 55~65℃ for 2~3h, and after the reaction is completed, filtering, washing and drying to prepare epoxidized starch.

[0011] Preferably, the plasticizer is glycerol; the starch is one or more of corn starch, potato starch, tapioca starch, and wheat starch.

[0012] Preferably, the method for preparing the modified nanocellulose includes the following steps:

[0013] A. Disperse nanocellulose in deionized water using ultrasonication, add Tris buffer to adjust the pH to 7.5-8, then add tannic acid and stir for 10-12 hours to prepare a nanocellulose dispersion.

[0014] B. The modified composite filler was ultrasonically dispersed in deionized water, and nanocellulose dispersion and zinc acetate dihydrate aqueous solution were added. The mixture was stirred at 40~50℃ for 4~7h. After the reaction was completed, the mixture was filtered, washed and dried to prepare modified nanocellulose.

[0015] Preferably, the preparation method of the modified composite filler in step B includes the following steps:

[0016] B1. Disperse fumed silica in ethanol using ultrasonication, then add tetrabutyl titanate and continue ultrasonic dispersion until uniform. Then slowly add deionized water and stir the reaction for 4-6 hours. After the reaction is complete, filter, wash, and dry the product. Grind the obtained solid product into a uniform powder and place it in a muffle furnace. Heat the powder to 550-600℃ at a heating rate of 1.5-2℃ / min and calcine for 4-6 hours to prepare the composite filler.

[0017] B2. The composite filler was ultrasonically dispersed in N,N-dimethylformamide to obtain a dispersion. Succinic anhydride, γ-aminopropyltriethoxysilane and N,N-dimethylformamide were stirred evenly and added to the dispersion. The mixture was stirred at 50~65℃ for 6~8h. After the reaction was completed, the mixture was filtered, washed and dried to prepare the carboxylated composite filler.

[0018] B3. Take the carboxylated composite filler and ultrasonically disperse it in deionized water. Add N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide and stir to mix. Then add polyethyleneimine aqueous solution, ultrasonically disperse it evenly, and continue to stir and react for 8-12 hours. After the reaction is completed, filter, wash and dry to prepare the aminated composite filler.

[0019] B4. Dodecyl dimethyl tertiary amine was placed in a reactor, epichlorohydrin was added, and the mixture was stirred at 55-65°C for 2-3 hours. After the reaction was completed, the organic solvent was removed by vacuum distillation. The mixture was then recrystallized with acetone, washed with anhydrous diethyl ether, and dried to prepare epichlorohydrin dodecyl dimethyl ammonium chloride.

[0020] B5. The aminated composite filler was ultrasonically dispersed in anhydrous ethanol, and glycidyl dodecyl dimethyl ammonium chloride was added. The mixture was stirred at 55-70℃ for 8-12 hours. After the reaction was completed, the filler was centrifuged, washed, and dried to obtain the modified composite filler.

[0021] Preferably, in step B1, the addition ratio of fumed silica, tetrabutyl titanate, and deionized water is 3~5g: 5~10mL: 150~250mL.

[0022] Preferably, in step B2, the mass ratio of the composite filler, succinic anhydride, and γ-aminopropyltriethoxysilane is 1:5~10:10~22.

[0023] Preferably, the concentration of the polyethyleneimine aqueous solution in step B3 is 8~15 mg / mL, and the addition ratio of the carboxylated composite filler to the polyethyleneimine aqueous solution is 1:50~100 mL.

[0024] Preferably, in step B5, the mass ratio of the aminated composite filler to glycidyl dodecyl dimethyl ammonium chloride is 1:2~5.

[0025] A method for preparing an epoxy-modified starch-based biodegradable film includes the following steps:

[0026] S1. Weigh each raw material according to the weight parts, put epoxidized starch and deionized water into a reactor, and stir and gelatinize at 60~70℃ to obtain an epoxidized starch solution with a mass fraction of 8~15%.

[0027] S2. The modified nanocellulose is ultrasonically dispersed in ethanol to obtain a modified nanocellulose dispersion with a mass fraction of 2-5%.

[0028] S3. Mix the epoxidized starch solution and the modified nanocellulose dispersion evenly, add the plasticizer, stir and mix evenly, then cast into a film, dry at 60~70℃ for 2~3h, and peel off the film after the temperature drops to room temperature to prepare an epoxy-modified starch-based biodegradable film.

[0029] The beneficial effects of this invention are:

[0030] This invention utilizes an alcohol dispersion hydrolysis method to uniformly coat nano-titanium dioxide onto the surface of fumed silica nanoparticles, preparing a composite filler with a large specific surface area. Then, the composite filler is modified by carboxylation using succinic anhydride and γ-aminopropyltriethoxysilane, followed by an amidation reaction with polyethyleneimine to prepare an aminated composite filler. Simultaneously, this invention utilizes a reaction between dodecyl dimethyl tertiary amine and epichlorohydrin to prepare epioxypropyl dodecyl dimethyl ammonium chloride, which is then chemically grafted onto the surface of the aminated composite filler via a ring-opening reaction for quaternization modification, thus preparing a modified composite filler. Furthermore, this invention utilizes polytannic acid formed by the oxidative self-polymerization of tannic acid to adhere to the surface of nanocellulose. Tannic acid is a natural polyphenol with a high density of pyrogallol and catechol groups, possessing not only antioxidant and strong adhesive properties but also certain antibacterial and flame-retardant effects. This invention mixes modified composite filler, nanocellulose dispersion, and zinc acetate dihydrate aqueous solution, and prepares modified nanocellulose in an aqueous phase through ion exchange and acid-base neutralization reactions. The tannic acid introduced into the nanocellulose dispersion can form a complex with zinc ions. The polyethyleneimine molecular chain introduced into the modified composite filler contains abundant primary, secondary, and tertiary amine functional groups, exhibiting a strong affinity for zinc ions. It exhibits chelating properties and can crosslink with hydroxyl groups in nanocellulose dispersions, improving the thermal stability, tensile properties, and flame retardant properties of starch-based film materials. Furthermore, the modified composite filler surface is strongly bonded with antibacterial quaternary ammonium salts and zinc ions, as well as hydrophobic alkyl long chains, preventing the long-term migration and loss of antibacterial materials and enhancing the hydrophobicity of the starch-based film material. This also facilitates the uniform dispersion of modified nanocellulose within the starch-based film material. The modified nanocellulose prepared in this invention combines the advantages of nano-titanium dioxide and organic antibacterial materials, exhibiting complementary and synergistic antibacterial effects, achieving strong antibacterial activity, good antibacterial stability, and long-lasting antibacterial action. Additionally, this invention uses epichlorohydrin to chemically modify starch, preparing epoxidized starch, which makes the modified nanocellulose and epoxidized starch more tightly bound, improving their compatibility and allowing both to fully exert their properties. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1: A method for preparing epoxidized starch includes the following steps:

[0033] 20g of dried corn starch was placed in a reactor, and 40mL of ethyl acetate, 5g of epichlorohydrin and 2g of pyridine were added. The mixture was stirred at 60℃ for 2h. After the reaction was completed, the starch was filtered, washed and dried to prepare epoxidized starch.

[0034] Example 2: A method for preparing a modified composite filler includes the following steps:

[0035] B1. Take 3g of fumed silica and ultrasonically disperse it in 250mL of ethanol. Then add 5mL of tetrabutyl titanate and continue to ultrasonically disperse it evenly. Then slowly add 150mL of deionized water and stir the reaction for 4h. After the reaction is completed, filter, wash and dry the product. Grind the obtained solid product into a uniform powder and place it in a muffle furnace to calcine at 600℃ for 4h at a heating rate of 2℃ / min to prepare the composite filler.

[0036] B2. Take 1g of composite filler and ultrasonically disperse it in 100mL of N,N-dimethylformamide to obtain a dispersion. Take 5g of succinic anhydride, 11g of γ-aminopropyltriethoxysilane and 25mL of N,N-dimethylformamide, stir evenly and add them to the dispersion. Place the mixture at 60℃ and stir for 8h. After the reaction is completed, filter, wash and dry to prepare carboxylated composite filler.

[0037] B3. Take 1g of carboxylated composite filler and ultrasonically disperse it in 120mL of deionized water. Add 1.5g of N-hydroxysuccinimide and 1.8g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide and stir to mix. Then add 60mL of 10mg / mL polyethyleneimine aqueous solution, ultrasonically disperse it evenly, and continue to stir and react for 10h. After the reaction is completed, filter, wash and dry to prepare aminated composite filler.

[0038] B4. Take 10.7g of dodecyl dimethyl tertiary amine into a reactor, add 23.3g of epichlorohydrin, stir and react at 60℃ for 2h. After the reaction is completed, remove the organic solvent by vacuum distillation, recrystallize with acetone, wash with anhydrous diethyl ether and dry to prepare epichlorohydrin dodecyl dimethyl ammonium chloride.

[0039] B5. Take 1g of aminated composite filler and ultrasonically disperse it in 100mL of anhydrous ethanol. Add 2.2g of glycidyl dodecyl dimethyl ammonium chloride and stir at 65℃ for 12h. After the reaction is completed, centrifuge, wash and dry to prepare the modified composite filler.

[0040] Example 3 A method for preparing modified nanocellulose includes the following steps:

[0041] A. Take 1g of nanocellulose and ultrasonically disperse it in 100mL of deionized water. Add 1mol / L Tris buffer to adjust the pH to 8, then add 1.3g of tannic acid and stir for 12h to prepare nanocellulose dispersion.

[0042] B. Take 1.2g of the modified composite filler prepared in Example 2 and ultrasonically disperse it in 100mL of deionized water. Add 40mL of nanocellulose dispersion and 20mL of 0.3g / mL zinc acetate dihydrate aqueous solution. Stir and react at 50℃ for 6h. After the reaction is completed, filter, wash and dry to prepare modified nanocellulose.

[0043] Example 4 An epoxy-modified starch-based biodegradable film, comprising the following components by weight: 55 parts of epoxidized starch prepared in Example 1, 7 parts of modified nanocellulose prepared in Example 3, and 16 parts of glycerol.

[0044] The preparation method of the above-mentioned epoxy-modified starch-based biodegradable film includes the following steps:

[0045] S1. Weigh each raw material according to the weight parts, take epoxidized starch and deionized water into the reactor, and stir and gelatinize at 70°C to obtain an epoxidized starch solution with a mass fraction of 12%.

[0046] S2. The modified nanocellulose was ultrasonically dispersed in ethanol to obtain a modified nanocellulose dispersion with a mass fraction of 5%.

[0047] S3. Mix the epoxidized starch solution and the modified nanocellulose dispersion evenly, add glycerol, stir and mix evenly, then cast into a film, dry at 70℃ for 2 hours, and peel off the film after the temperature drops to room temperature to prepare an epoxy-modified starch-based biodegradable film.

[0048] Example 5 An epoxy-modified starch-based biodegradable film, comprising the following components by weight: 62 parts of epoxidized starch prepared in Example 1, 10 parts of modified nanocellulose prepared in Example 3, and 20 parts of glycerol.

[0049] The preparation method of the above-mentioned epoxy-modified starch-based biodegradable film is described in Example 4.

[0050] Example 6 An epoxy-modified starch-based biodegradable film, comprising the following components by weight: 68 parts of epoxidized starch prepared in Example 1, 13 parts of modified nanocellulose prepared in Example 3, and 22 parts of glycerol.

[0051] The preparation method of the above-mentioned epoxy-modified starch-based biodegradable film is described in Example 4.

[0052] Comparative Example 1: A method for preparing a modified composite filler includes the following steps:

[0053] B1. Take 3g of fumed silica and ultrasonically disperse it in 250mL of ethanol. Then add 5mL of tetrabutyl titanate and continue to ultrasonically disperse it evenly. Then slowly add 150mL of deionized water and stir the reaction for 4h. After the reaction is completed, filter, wash and dry the product. Grind the obtained solid product into a uniform powder and place it in a muffle furnace to calcine at 600℃ for 4h at a heating rate of 2℃ / min to prepare the composite filler.

[0054] B2. Take 1g of composite filler and ultrasonically disperse it in 100mL of N,N-dimethylformamide to obtain a dispersion. Take 5g of succinic anhydride, 11g of γ-aminopropyltriethoxysilane and 25mL of N,N-dimethylformamide, stir evenly and add them to the dispersion. Place the mixture at 60℃ and stir for 8h. After the reaction is completed, filter, wash and dry to prepare carboxylated composite filler.

[0055] B3. Take 1g of carboxylated composite filler and ultrasonically disperse it in 120mL of deionized water. Add 1.5g of N-hydroxysuccinimide and 1.8g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide and stir to mix. Then add 60mL of 10mg / mL polyethyleneimine aqueous solution, ultrasonically disperse it evenly, and continue to stir and react for 10h. After the reaction is completed, filter, wash and dry to prepare the modified composite filler.

[0056] Comparative Example 2: A method for preparing modified nanocellulose includes the following steps:

[0057] A. Take 1g of nanocellulose and ultrasonically disperse it in 100mL of deionized water. Add 1mol / L Tris buffer to adjust the pH to 8, then add 1.3g of tannic acid and stir for 12h to prepare nanocellulose dispersion.

[0058] B. Take 1.2g of the modified composite filler prepared in Comparative Example 1 and ultrasonically disperse it in 100mL of deionized water. Add 40mL of nanocellulose dispersion and 20mL of 0.3g / mL zinc acetate dihydrate aqueous solution. Stir and react at 50℃ for 6h. After the reaction is completed, filter, wash and dry to prepare modified nanocellulose.

[0059] Comparative Example 3: A method for preparing modified nanocellulose includes the following steps:

[0060] A. Take 1g of nanocellulose and ultrasonically disperse it in 100mL of deionized water. Add 1mol / L Tris buffer to adjust the pH to 8, then add 1.3g of tannic acid and stir for 12h to prepare nanocellulose dispersion.

[0061] B. Take 1.2g of the composite filler prepared in Example 2 and ultrasonically disperse it in 100mL of deionized water. Add 40mL of nanocellulose dispersion and 20mL of 0.3g / mL zinc acetate dihydrate aqueous solution. Stir and react at 50℃ for 6h. After the reaction is completed, filter, wash and dry to prepare modified nanocellulose.

[0062] Comparative Example 4: An epoxy-modified starch-based biodegradable film comprising the following components by weight: 68 parts of epoxidized starch prepared in Example 1, 13 parts of modified nanocellulose prepared in Comparative Example 2, and 22 parts of glycerol.

[0063] The preparation method of the above-mentioned epoxy-modified starch-based biodegradable film is described in Example 4.

[0064] Comparative Example 5: An epoxy-modified starch-based biodegradable film comprising the following components by weight: 68 parts of epoxidized starch prepared in Example 1, 13 parts of modified nanocellulose prepared in Comparative Example 3, and 22 parts of glycerol.

[0065] The preparation method of the above-mentioned epoxy-modified starch-based biodegradable film is described in Example 4.

[0066] Comparative Example 6: An epoxy-modified starch-based biodegradable membrane, comprising the following components by weight: 68 parts of epoxidized starch prepared in Example 1, 7 parts of modified composite filler prepared in Example 2, 6 parts of nanocellulose, and 22 parts of glycerol.

[0067] The preparation method of the above-mentioned epoxy-modified starch-based biodegradable film is described in Example 4.

[0068] Performance testing

[0069] The performance of the epoxy-modified starch-based biodegradable films prepared in Examples 4-6 and Comparative Examples 4-6 was tested.

[0070] (1) Tensile property test: The tensile properties were tested using a universal testing machine. The longitudinal tension was 2 mm / min, and the data results are shown in Table 1.

[0071] (2) Heat resistance test: Thermogravimetric analysis was used to test the thermal stability under nitrogen atmosphere and heating rate of 10℃ / min. The data results are shown in Table 1.

[0072] (3) Water contact angle detection: Under the same environmental conditions, the water contact angle of the film was detected by a contact angle analyzer, and the data results are shown in Table 1.

[0073] (4) Flame retardant performance test: The flame retardant performance of the samples was evaluated by the limiting oxygen index, and the data results are shown in Table 1.

[0074] (5) Antibacterial performance test: The antibacterial effect against Escherichia coli and Staphylococcus aureus was tested by plate counting method. Equal masses of film were weighed and dispersed in bacterial suspension. After incubation at 25℃ for 8 hours, the bacterial suspension was diluted to a total bacterial count of 10. 6 CFU / mL was evenly spread on agar medium and incubated at 37℃ for 24h. The number of colonies corresponding to different samples was observed. The film inhibition rate (K) was calculated as follows: K=(N1-N2) / N1, where N1 is the number of surviving colonies in the blank control group and N2 is the number of surviving colonies in the sample group. The data results are shown in Table 1.

[0075] Table 1 Test results of sample performance

[0076]

[0077] As can be seen from the data in Table 1, the membrane materials prepared in Examples 4-6 of the present invention have high tensile strength, certain hydrophobicity, and good heat resistance, antibacterial properties and flame retardant properties. In Comparative Example 4, the modified nanocellulose component introduced a modified composite filler that was not grafted with glycidyl dodecyl dimethyl ammonium chloride. Its measured antibacterial rate and water contact angle were lower than those of Examples 4-6. This is because the grafting of glycidyl dodecyl dimethyl ammonium chloride introduces quaternary ammonium salt antibacterial groups and hydrophobic alkyl long chains, which helps improve the antibacterial and hydrophobic properties of the membrane material. In Comparative Example 5, the modified nanocellulose component was not modified with the composite filler. Its measured tensile strength, heat resistance, hydrophobicity, antibacterial properties, and flame retardant properties were lower than those of Examples 4-6, indicating that modifying the composite filler is beneficial to improving the overall performance of the membrane material. In Comparative Example 6, the modified composite filler and nanocellulose were simply mixed. Its measured antibacterial rate and limiting oxygen index were lower than those of Examples 4-6, indicating that the introduction of tannic acid and zinc acetate dihydrate is beneficial to improving the antibacterial and flame retardant properties of the membrane material.

[0078] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0079] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. An epoxy-modified starch-based biodegradable film, characterized in that, It includes the following components by weight: 50-70 parts of epoxidized starch, 5-15 parts of modified nanocellulose, and 15-25 parts of plasticizer; The modified nanocellulose is prepared by mixing modified composite filler, nanocellulose dispersion, and zinc acetate dihydrate aqueous solution in an aqueous phase through ion exchange and acid-base neutralization reaction; wherein the nanocellulose dispersion is prepared by tannic acid oxidation self-polymerization to form polytannic acid that adheres to the surface of nanocellulose. The modified composite filler is prepared by carboxylating fumed silica nanoparticles coated with nano-titanium dioxide using succinic anhydride and γ-aminopropyltriethoxysilane, followed by an amidation reaction with polyethyleneimine to obtain an aminated composite filler, and finally quaternization modification by chemically grafting glycidyl dodecyl dimethyl ammonium chloride onto the surface of the aminated composite filler using a ring-opening reaction.

2. The epoxy-modified starch-based biodegradable film according to claim 1, characterized in that, The preparation method of the epoxidized starch includes the following steps: take dry starch in a reactor, add ethyl acetate, epichlorohydrin and pyridine, stir and react at 55~65℃ for 2~3h, and after the reaction is completed, filter, wash and dry to prepare epoxidized starch.

3. The epoxy-modified starch-based biodegradable film according to claim 1, characterized in that, The plasticizer is glycerol; the starch is one or more of corn starch, potato starch, cassava starch, and wheat starch.

4. The epoxy-modified starch-based biodegradable film according to claim 1, characterized in that, The preparation method of the modified nanocellulose includes the following steps: A. Disperse nanocellulose in deionized water using ultrasonication, add Tris buffer to adjust the pH to 7.5-8, then add tannic acid and stir for 10-12 hours to prepare nanocellulose dispersion. B. The modified composite filler was ultrasonically dispersed in deionized water, and nanocellulose dispersion and zinc acetate dihydrate aqueous solution were added. The mixture was stirred at 40~50℃ for 4~7h. After the reaction was completed, the mixture was filtered, washed and dried to prepare modified nanocellulose.

5. The epoxy-modified starch-based biodegradable film according to claim 4, characterized in that, The preparation method of the modified composite filler in step B includes the following steps: B1. Disperse fumed silica in ethanol using ultrasonication, then add tetrabutyl titanate and continue ultrasonic dispersion until uniform. Then slowly add deionized water and stir the reaction for 4-6 hours. After the reaction is complete, filter, wash, and dry the product. Grind the obtained solid product into a uniform powder and place it in a muffle furnace. Heat the powder to 550-600℃ at a heating rate of 1.5-2℃ / min and calcine for 4-6 hours to prepare the composite filler. B2. The composite filler was ultrasonically dispersed in N,N-dimethylformamide to obtain a dispersion. Succinic anhydride, γ-aminopropyltriethoxysilane and N,N-dimethylformamide were stirred evenly and added to the dispersion. The mixture was stirred at 50~65℃ for 6~8h. After the reaction was completed, the mixture was filtered, washed and dried to prepare the carboxylated composite filler. B3. Take the carboxylated composite filler and ultrasonically disperse it in deionized water. Add N-hydroxysuccinimide and 1-ethyl-(3-dimethylaminopropyl)carbodiimide and stir to mix. Then add polyethyleneimine aqueous solution, ultrasonically disperse it evenly, and continue to stir and react for 8-12 hours. After the reaction is completed, filter, wash and dry to prepare the aminated composite filler. B4. Dodecyl dimethyl tertiary amine was placed in a reactor, epichlorohydrin was added, and the mixture was stirred at 55-65°C for 2-3 hours. After the reaction was completed, the organic solvent was removed by vacuum distillation. The mixture was then recrystallized with acetone, washed with anhydrous diethyl ether, and dried to prepare epichlorohydrin dodecyl dimethyl ammonium chloride. B5. The aminated composite filler was ultrasonically dispersed in anhydrous ethanol, and glycidyl dodecyl dimethyl ammonium chloride was added. The mixture was stirred at 55-70℃ for 8-12 hours. After the reaction was completed, the filler was centrifuged, washed, and dried to obtain the modified composite filler.

6. The epoxy-modified starch-based biodegradable film according to claim 5, characterized in that, In step B1, the addition ratio of fumed silica, tetrabutyl titanate, and deionized water is 3~5g: 5~10mL: 150~250mL.

7. The epoxy-modified starch-based biodegradable film according to claim 5, characterized in that, In step B2, the mass ratio of the composite filler, succinic anhydride, and γ-aminopropyltriethoxysilane is 1:5~10:10~22.

8. The epoxy-modified starch-based biodegradable film according to claim 5, characterized in that, In step B3, the concentration of the polyethyleneimine aqueous solution is 8~15 mg / mL, and the addition ratio of the carboxylated composite filler to the polyethyleneimine aqueous solution is 1:50~100 mL.

9. The epoxy-modified starch-based biodegradable film according to claim 5, characterized in that, In step B5, the mass ratio of the aminated composite filler to glycidyl dodecyl dimethyl ammonium chloride is 1:2~5.

10. A method for preparing an epoxy-modified starch-based biodegradable film according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Weigh each raw material according to the weight parts, put epoxidized starch and deionized water into a reactor, and stir and gelatinize at 60~70℃ to obtain an epoxidized starch solution with a mass fraction of 8~15%. S2. The modified nanocellulose is ultrasonically dispersed in ethanol to obtain a modified nanocellulose dispersion with a mass fraction of 2-5%. S3. Mix the epoxidized starch solution and the modified nanocellulose dispersion evenly, add the plasticizer, stir and mix evenly, then cast into a film, dry at 60~70℃ for 2~3h, and peel off the film after the temperature drops to room temperature to prepare an epoxy-modified starch-based biodegradable film.

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