Water-based degradable bio-based coating and preparation method thereof

Abstract

The invention relates to the field of coatings, and provides a water-based degradable bio-based coating and a preparation method thereof.The water-based degradable bio-based coating is prepared from, by weight, 35-50 parts of bio-based resin emulsion, 5-15 parts of composite filler, 0.1-1 part of defoaming agent, 0.5-2 parts of flatting agent and 25-40 parts of deionized water, the composite filler is a mixture of modified nano silicon dioxide and nano montmorillonite. The coating provided by the invention has the characteristics of degradability and good scratch resistance.

Description

Technical Field

[0001] The present invention relates to the field of coatings, and particularly to an aqueous degradable bio-based coating and a preparation method thereof. Background Art

[0002] In recent years, with the gradual improvement of the level of modern industrial construction, the requirements for environmental protection and sustainable development of chemical enterprises have become increasingly high. Degradable materials refer to organic materials that can be naturally decomposed. Under the action of microorganisms, biochemical reactions occur, causing various changes such as changes in appearance to internal quality, and ultimately forming common compounds in nature such as carbon dioxide and water. Degradable materials follow the principle of environmental protection, reduce environmental pollution, and can promote sustainable development to a greater extent.

[0003] Waterborne coatings use water as the dispersion medium, replacing organic solvents that have a great impact on the environment, and have practical significance for environmental protection. Among them, waterborne polyurethane, which uses water instead of organic solvents as the dispersion medium, has gradually developed as an environmentally friendly polymer. Although the pollution toxicity of waterborne polyurethane materials is very low, environmental pollution will still be caused when they are recycled by incineration or landfill. Therefore, the development of degradable bio-based waterborne polyurethane has become increasingly important. In addition, the wear resistance and scratch resistance of waterborne polyurethane still need to be improved, thereby increasing the service life of waterborne polyurethane.

[0004] Patent CN 104263100B discloses a scratch-resistant automotive coating and a preparation method thereof. The components of the coating include polypropylene resin, polyurethane acrylate, polyurethane, calcium carbonate, silica, polysiloxane, erucic acid amide, hydroxyethyl cellulose, pigments, and inorganic fillers. Although calcium carbonate and silica can improve the scratch resistance of the coating, both of them have poor dispersion problems, which may lead to the scratch resistance of the coating not reaching the ideal effect.

[0005] Therefore, there is an urgent need in the market for an aqueous degradable bio-based coating with good scratch resistance. Summary of the Invention

[0006] Aiming at the problems existing in the prior art, the present invention uses a bio-based resin emulsion as the main component of the coating, and synthesizes an aqueous degradable bio-based coating with composite fillers, defoamers, leveling agents, and deionized water, which has the characteristic of good scratch resistance.

[0007] In order to achieve the above object, the technical solutions adopted by the present invention are as follows:

[0008] On the one hand, the present invention provides an aqueous degradable bio-based coating. By weight, the coating comprises the following raw materials: 35-50 parts of bio-based resin emulsion, 5-15 parts of composite filler, 0.1-1 part of defoamer, 0.5-2 parts of leveling agent, 25-40 parts of deionized water, wherein the composite filler is a mixture of modified nano-silica and nano-montmorillonite.

[0009] In some embodiments of the present invention, by weight, the bio-based resin emulsion comprises the following raw materials: 20-30 parts of polylactic acid diol, 5-15 parts of hydroxypropyl cellulose, 30-50 parts of isophorone diisocyanate, 0.05-2 parts of stannous octoate, 1-4 parts of N-methyldiethanolamine, 1-5 parts of 1,6-hexanediol, 20-30 parts of acetone, 50-70 parts of deionized water.

[0010] In some embodiments of the present invention, the preparation method of the bio-based resin emulsion comprises the following steps:

[0011] (1) Add polylactic acid diol and hydroxypropyl cellulose into a reaction vessel, stir and heat up to 100-110 °C under reduced pressure for 2-3 h, cool down to 80-90 °C, add isophorone diisocyanate under an inert atmosphere, stir for 1-2 h, add stannous octoate, stir for 2.5-3.5 h, cool down to 55-65 °C, add N-methyldiethanolamine, stir for 40-70 min, heat up to 80-90 °C, add 1,6-hexanediol and acetone, stir for 2.5-3.5 h to obtain a prepolymer for standby;

[0012] (2) Cool down the prepolymer obtained in step (1) to 30-40 °C, adjust the pH = 6-6.5, stir, add deionized water, stir, and perform vacuum distillation to obtain the bio-based resin emulsion.

[0013] In some embodiments of the present invention, the mass ratio of isophorone diisocyanate, polylactic acid diol and hydroxypropyl cellulose is 1:(0.55-0.7):(0.2-0.4).

[0014] The applicant selects polylactic acid diol, hydroxypropyl cellulose and isophorone diisocyanate as reaction raw materials, controls the ratio among the three, introduces polylactic acid chain segments and carboxymethyl cellulose chain segments into the polyurethane molecular chain segments, so that the resin structure contains a segment structure that can be naturally degraded, and reacts polylactic acid diol, hydroxypropyl cellulose and isophorone diisocyanate with components such as solution, catalyst, chain extender, etc. to synthesize a bio-based resin emulsion, making the coating have the characteristics of bio-based degradability.

[0015] In some embodiments of the present invention, the mass ratio of modified nano-silica and nano-montmorillonite in the composite filler is 1:(1.5-3).

[0016] Preferably, the mass ratio of the modified nano-silica to the nano-montmorillonite in the composite filler is 1:2.

[0017] The applicant compounded the modified nano-silica and the nano-montmorillonite in a specific ratio to obtain a composite filler. The nano-montmorillonite has a two-dimensional lamellar structure, which can improve the dispersibility of the nano-silica to a certain extent and also improve the toughness of the coating. The improvement of toughness can enhance the resistance of the coating to external friction, reduce the damage of the coating when scratched, and thus improve the scratch resistance of the coating.

[0018] In some embodiments of the present invention, the preparation method of the modified nano-silica includes the following steps:

[0019] 1) Mix potato starch and sodium hydroxide, add an ethanol aqueous solution, stir, heat to 30 - 40 °C, stir, add glycidyl in an inert atmosphere, heat to 40 - 50 °C, stir, adjust the pH = 7 - 7.5, filter, wash, dry, and pulverize to obtain modified starch for standby;

[0020] 2) Mix the modified starch from step 1) and deionized water, stir to obtain a mixed solution for standby. Add nano-silica to deionized water, ultrasonicate, add the mixed solution, stir, filter, dry, and grind to obtain a product for standby;

[0021] 3) Add the product from step 2) to deionized water, stir, add N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, stir, spray dry, heat at 240 - 260 °C for 1 - 3 h, wash, and dry to obtain the modified nano-silica.

[0022] In some embodiments of the present invention, in step 1), the mass ratio of potato starch to glycidyl is 1:(0.1 - 0.4).

[0023] Preferably, in step 1), the mass ratio of potato starch to glycidyl is 1:0.25.

[0024] In some embodiments of the present invention, in step 2), the mass ratio of nano-silica to modified starch is 1:(0.2 - 0.5).

[0025] Preferably, in step 2), the mass ratio of nano-silica to modified starch is 1:0.33.

[0026] In some embodiments of the present invention, in step 3), the mass ratio of the product to N-(2-aminoethyl)-3-aminopropyltrimethoxysilane is 1:(0.05 - 0.3).

[0027] Preferably, in the step 3), the mass ratio of the product to N-(2-aminoethyl)-3-aminopropyltrimethoxysilane is 1:0.15.

[0028] In this application, a bio-based resin emulsion synthesized from polylactic acid diol, hydroxypropyl cellulose, and isophorone diisocyanate is used as the main raw material of the coating. Its main component is polyurethane. Under the action of external forces, scratches and cracks are likely to appear on the surface of the polyurethane resin, causing the coating to lose its protective effect or affect its appearance. Therefore, its scratch resistance still needs to be improved. Due to the excellent properties of nano-silica such as high hardness and high wear resistance, adding it to the polyurethane coating can effectively improve the scratch resistance of the coating. However, nano-silica has problems such as easy agglomeration and poor dispersibility, resulting in the scratch resistance of the coating not being improved ideally.

[0029] On the one hand, the applicant uses potato starch as the raw material. Under alkaline conditions, modified starch is prepared through the etherification reaction between starch and glycidyl, introducing a distal hydroxyl structure into the starch, thereby increasing the hydroxyl content in the starch structure. Further, the applicant modifies nano-silica with the modified starch. A large number of hydroxyl functional groups in the modified starch structure can be grafted onto the particles of nano-silica in the form of hydrogen bonds, thereby effectively improving the dispersibility of nano-silica. And the steric hindrance effect of starch can prevent the aggregation of nano-silica particles to a certain extent, improving the dispersibility and compatibility of nano-silica particles in the water-based coating, and thus effectively improving the scratch resistance of the coating. Furthermore, the introduction of the modified starch can also improve the adhesion and impact resistance of the coating, indirectly improving the scratch resistance of the coating. On the other hand, the applicant selects the silane coupling agent N-(2-aminoethyl)-3-aminopropyltrimethoxysilane to modify the product, further improving the dispersibility of nano-silica, and thus effectively improving the scratch resistance of the coating.

[0030] In some embodiments of the present invention, the defoaming agent is an organosilicon defoaming agent.

[0031] In some embodiments of the present invention, the leveling agent is leveling agent PV88.

[0032] On the other hand, the present invention also provides a preparation method of the water-based degradable bio-based coating described in the above technical solution, including the following steps:

[0033] Mix the bio-based resin emulsion and deionized water, stir for 10 - 20 min, then add the defoaming agent and the leveling agent, stir for 2 - 5 min, add the composite filler, and stir for 20 - 40 min to obtain the water-based degradable bio-based coating.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] (1) The present invention uses a bio - based resin emulsion as the main component of the coating, and adds composite fillers, defoamers, leveling agents and deionized water to synthesize an aqueous degradable bio - based coating, which has the characteristic of good scratch resistance.

[0036] (2) The present invention selects polylactic acid diol, hydroxypropyl cellulose and isophorone diisocyanate as reaction raw materials, controls the ratio among the three, introduces polylactic acid chain segments and carboxymethyl cellulose chain segments into the polyurethane molecular chain segments, so that the resin structure contains a segment structure that can be naturally degraded, and makes the coating have the characteristic of bio - based degradability.

[0037] (3) The present invention uses potato starch as the raw material, under alkaline conditions, prepares modified starch through the etherification reaction between starch and glycidyl, then modifies nano - silica with the modified starch, and finally introduces the silane coupling agent N - (2 - aminoethyl) - 3 - aminopropyltrimethoxysilane for modification, effectively improving the dispersibility of nano - silica, and further effectively improving the scratch resistance of the coating.

[0038] (4) The coating prepared by the present invention has the characteristics of degradability and good scratch resistance, and can be widely applied to the field of aqueous degradable bio - based coatings, having good commercial application value. Detailed Embodiments

[0039] The following will describe the present invention in combination with specific implementation examples. It should be noted that the following examples are examples of the present invention, only used to illustrate the present invention, rather than to limit the present invention. Without departing from the gist or scope of the present invention, other combinations and various improvements within the concept of the present invention can be made.

[0040] In the following examples and comparative examples, except for the bio - based resin emulsion and modified nano - silica, the other compound monomers and related reagents used can be purchased from the market. Among them, the average number - average molecular weight of polylactic acid diol is 2000, purchased from Wuhan Lanabai Pharmaceutical Chemical Co., Ltd.; hydroxypropyl cellulose is purchased from Shenzhen Love Biotechnology Co., Ltd.; nano - montmorillonite is Fenghong DK2, purchased from Zhejiang Fenghong New Materials Co., Ltd.; silicone defoamer is purchased from Dongguan Yuanya New Materials Co., Ltd.; leveling agent PV88 is purchased from Foshan Jieke New Materials Co., Ltd.

[0041] Preparation Example 1

[0042] The synthesis method of bio - based resin emulsion A includes the following steps:

[0043] (1) Add 25 g of polylactic acid diol and 10 g of hydroxypropyl cellulose into a reaction vessel. While stirring, heat up to 105 °C and reduce the pressure for 2.5 h. Then cool down to 85 °C. Under a nitrogen atmosphere, add 40 g of isophorone diisocyanate, stir for 1.5 h, add 0.08 g of stannous octoate, stir for 3 h, cool down to 60 °C, add 2 g of N-methyldiethanolamine, stir for 60 min, heat up to 85 °C, add 3 g of 1,6-hexanediol and 20 ml of acetone, and stir for 3 h to obtain a prepolymer for standby.

[0044] (2) Cool down the prepolymer obtained in step (1) to 35 °C, add an aqueous solution of 37 wt% hydrochloric acid to adjust the pH to 6.1, stir for 30 min, add 60 ml of deionized water, stir for 3 h, and perform vacuum distillation to obtain the bio-based resin emulsion A.

[0045] Preparation Example 2

[0046] Bio-based resin emulsion B, the specific implementation method is the same as that of bio-based resin emulsion A, the difference is that: in step (1), the mass of polylactic acid diol is replaced with 20 g.

[0047] Preparation Example 3

[0048] Bio-based resin emulsion C, the specific implementation method is the same as that of bio-based resin emulsion A, the difference is that: in step (1), the mass of hydroxypropyl cellulose is replaced with 6 g.

[0049] Preparation Example 4

[0050] The synthesis method of modified nano-silica A includes the following steps:

[0051] 1) Mix 10 g of potato starch and 0.35 g of sodium hydroxide, add 40 ml of 85 wt% ethanol aqueous solution, stir for 30 min, heat up to 35 °C, stir for 2 h. Under a nitrogen atmosphere, add 2.5 g of glycidyl, heat up to 45 °C, stir for 8 h, add 1 mol / L hydrochloric acid aqueous solution to adjust the pH to 7.2, perform suction filtration, wash with 80 wt% ethanol aqueous solution for 3 times, dry at 50 °C for 12 h, and pulverize to obtain modified starch for standby.

[0052] 2) Mix 5 g of the modified starch obtained in step 1) and 20 ml of deionized water, stir for 30 min to obtain a mixed solution for standby. Add 15 g of nano-silica into 100 ml of deionized water, perform ultrasonic treatment for 30 min, add the mixed solution, stir for 20 h, filter, dry at 50 °C for 12 h, and grind to obtain the product for standby.

[0053] 3) Add the 10 g of the product from step 2) to 100 ml of deionized water, stir for 30 min, add 1.5 g of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, stir for 2 h, spray dry, heat at 250 °C for 2 h, wash with absolute ethanol three times, and dry at 60 °C for 12 h to obtain modified nano-silica A.

[0054] Preparation Example 5

[0055] Modified nano-silica B, the specific implementation method is the same as that of modified nano-silica A, the difference is that: in step 1), the mass of glycidyl is replaced with 0.8 g.

[0056] Preparation Example 6

[0057] Modified nano-silica C, the specific implementation method is the same as that of modified nano-silica A, the difference is that: in step 2), the mass of modified starch is replaced with 2.7 g.

[0058] Preparation Example 7

[0059] Modified nano-silica D, the specific implementation method is the same as that of modified nano-silica A, the difference is that: in step 3), the mass of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane is replaced with 0.3 g.

[0060] Example 1

[0061] An aqueous degradable bio-based coating, by weight, the coating comprises the following raw materials: 40 parts of bio-based resin emulsion A, 10 parts of composite filler, 0.5 part of defoamer, 1 part of leveling agent, 35 parts of deionized water, wherein the composite filler is a mixture of modified nano-silica A and nano-montmorillonite, and the mass ratio is 1:2.

[0062] The preparation method of the aqueous degradable bio-based coating in this example comprises the following steps:

[0063] Mix the bio-based resin emulsion and deionized water, stir for 15 min, then add the defoamer and leveling agent, stir for 3 min, and add the composite filler, stir for 30 min to obtain the aqueous degradable bio-based coating.

[0064] Example 2

[0065] An aqueous degradable bio-based coating, by weight, the coating comprises the following raw materials: 35 parts of bio-based resin emulsion A, 5 parts of composite filler, 0.1 part of defoamer, 0.5 part of leveling agent, 25 parts of deionized water, wherein the composite filler is a mixture of modified nano-silica A and nano-montmorillonite, and the mass ratio is 1:1.5.

[0066] In this embodiment, the preparation method of the waterborne degradable bio-based coating comprises the following steps:

[0067] Mix the bio-based resin emulsion and deionized water, stir for 10 min, then add the defoaming agent and the leveling agent, stir for 2 min, add the composite filler, and stir for 20 min to obtain the waterborne degradable bio-based coating.

[0068] Example 3

[0069] A waterborne degradable bio-based coating, by weight, the coating comprises the following raw materials: 50 parts of bio-based resin emulsion A, 15 parts of composite filler, 1 part of defoaming agent, 2 parts of leveling agent, 40 parts of deionized water, wherein the composite filler is a mixture of modified nano-silica A and nano-montmorillonite, and the mass ratio is 1:3.

[0070] In this embodiment, the preparation method of the waterborne degradable bio-based coating comprises the following steps:

[0071] Mix the bio-based resin emulsion and deionized water, stir for 20 min, then add the defoaming agent and the leveling agent, stir for 5 min, add the composite filler, and stir for 40 min to obtain the waterborne degradable bio-based coating.

[0072] Example 4

[0073] This embodiment provides a waterborne degradable bio-based coating and its preparation method. The specific implementation manner is the same as that of Embodiment 1, except that bio-based resin emulsion B is used to replace bio-based resin emulsion A in equal amount.

[0074] Example 5

[0075] This embodiment provides a waterborne degradable bio-based coating and its preparation method. The specific implementation manner is the same as that of Embodiment 1, except that bio-based resin emulsion C is used to replace bio-based resin emulsion A in equal amount.

[0076] Example 6

[0077] This embodiment provides a waterborne degradable bio-based coating and its preparation method. The specific implementation manner is the same as that of Embodiment 1, except that modified nano-silica B is used to replace modified nano-silica A in equal amount.

[0078] Example 7

[0079] This embodiment provides a waterborne degradable bio-based coating and its preparation method. The specific implementation manner is the same as that of Embodiment 1, except that modified nano-silica C is used to replace modified nano-silica A in equal amount.

[0080] Example 8

[0081] This embodiment provides an aqueous degradable bio-based coating and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that modified nano-silica D is used to replace modified nano-silica A in equal amounts.

[0082] Comparative Example 1

[0083] This comparative example provides an aqueous degradable bio-based coating and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that nano-silica is used to replace modified nano-silica A in equal amounts.

[0084] Comparative Example 2

[0085] This comparative example provides an aqueous degradable bio-based coating and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that modified nano-silica A is used to replace the composite filler in equal amounts.

[0086] Comparative Example 3

[0087] This comparative example provides an aqueous degradable bio-based coating and a preparation method thereof. The specific implementation manner is the same as that of Example 1, except that nano-montmorillonite is used to replace the composite filler in equal amounts.

[0088] Performance testing

[0089] The degradability and scratch resistance of the aqueous degradable bio-based coatings of the above Examples 1-6 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1.

[0090] (1) Degradability

[0091] The test was carried out according to the test method provided by the national standard GB / T 19277.1-2011 "Determination of the ultimate aerobic biodegradability of materials under controlled composting conditions - Method by measuring the evolved carbon dioxide - Part 1: General method".

[0092] The main test principle of this method is as follows: Simulating the strong aerobic composting conditions, the ultimate aerobic biodegradability of the test material is determined. Activated vermiculite (equivalent to mature fertilizer, containing a large amount of active microorganisms) is used as the culture medium. The cut printed fabric sample is mixed with the culture medium and placed in a constant temperature incubator at 58 ± 2 °C for cultivation. At the same time, oxygen is introduced to maintain the survival and activity of microorganisms. Microorganisms decompose the coating, producing substances such as CO2, water, and mineral salts. The CO2 is collected, and the ratio of the actual amount of CO2 produced by the sample in the test to the theoretical amount of CO2 that the sample can produce is called the biodegradation percentage.

[0093] (2) Scratch resistance

[0094] The coatings obtained from the examples and comparative examples were applied to tinplate sheets with a thickness of 25 μm, and after drying and curing at 60 °C, the scratch resistance performance of the coatings was tested.

[0095] Referring to standard GMW14688, a German ERICHSEN 430P-1 electric cross-cut instrument was used to cross-cut the coating surface. A 0.5 mm scratch head was used, and at a pressure of 5 N, the coating was scratched at a speed of 1000 mm / min with 20 scratches spaced 4 mm apart and 40 mm in length. After cross-cutting in one direction, the plastic plate was rotated 90° and cross-cut again. The change in gloss (ΔL) before and after cross-cutting of the specimen was measured using a Dutch TQC GL0010 glossmeter to determine the scratch resistance performance of the coating surface. The smaller the change in gloss before and after, the better the scratch resistance performance of the coating surface.

[0096] Table 1

[0097]

[0098] From the data in Table 1, it can be seen that in Examples 1-3 of the present invention, the waterborne degradable bio-based coatings had a small change in gloss, indicating overall good degradable performance and scratch resistance performance. Among them, in Examples 4-5, the addition ratios of polylactic acid diol and hydroxypropyl cellulose in the synthesis process of the bio-based resin emulsion were changed, resulting in a decrease in the degradable performance of the bio-based resin emulsion, and further leading to a certain degree of decrease in the degradable performance of the coating, but it had no obvious impact on the scratch resistance performance; in Examples 6-8, the modification ratio of glycidyl to potato starch, the ratio between the modified starch and nano-silica, and the addition ratio of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane in the synthesis process of the modified nano-silica were changed, resulting in poor improvement of the dispersibility of the modified nano-silica, and further leading to a decrease in the scratch resistance performance of the coating, but it had no obvious impact on the degradable performance; in Comparative Examples 1-3, nano-silica was respectively selected to replace the modified nano-silica A in equal amount, and the modified nano-silica A and nano-montmorillonite were selected to replace the composite filler in equal amount. It was found that the scratch resistance performance of the coatings showed poor results, but it had little impact on the degradable performance of the coatings.

[0099] The above embodiments are only used to illustrate the technical concept and characteristics of the present invention, and the purpose is to enable those who are familiar with this technology to understand the content of the present invention and implement it. It cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A water-based biodegradable coating, characterized in that: The coating comprises the following raw materials by weight: 35-50 parts of bio-based resin emulsion, 5-15 parts of composite filler, 0.1-1 parts of defoamer, 0.5-2 parts of leveling agent, and 25-40 parts of deionized water, wherein the composite filler is a mixture of modified nano-silicon dioxide and nano-montmorillonite.

2. The water-based biodegradable coating according to claim 1, characterized in that: The bio-based resin emulsion comprises the following raw materials by weight: 20-30 parts of polylactic acid diol, 5-15 parts of hydroxypropyl cellulose, 30-50 parts of isophorone diisocyanate, 0.05-2 parts of stannous octoate, 1-4 parts of N-methyldiethanolamine, 1-5 parts of 1,6-hexanediol, 20-30 parts of acetone, and 50-70 parts of deionized water.

3. The water-based biodegradable coating according to claim 2, characterized in that: The preparation method of the bio-based resin emulsion comprises the following steps: (1) adding polylactic acid diol and hydroxypropyl cellulose to a reaction vessel, heating to 100-110° C. and reducing pressure for 2-3 hours while stirring, cooling to 80-90° C., adding isophorone diisocyanate under an inert atmosphere, stirring for 1-2 hours, adding stannous octoate, stirring for 2.5-3.5 hours, cooling to 55-65° C., adding N-methyldiethanolamine, stirring for 40-70 minutes, heating to 80-90° C., adding 1,6-hexanediol and acetone, stirring for 2.5-3.5 hours, and obtaining a prepolymer for standby use; (2) Cooling the prepolymer of step (1) to 30-40° C., adjusting the pH to 6-6.5, stirring, adding deionized water, stirring, and distilling under reduced pressure to obtain a bio-based resin emulsion.

4. The water-based biodegradable coating according to claim 1, characterized in that: The mass ratio of modified nano silicon dioxide to nano montmorillonite in the composite filler is 1:(1.5-3).

5. The water-based biodegradable coating according to claim 1, characterized in that: The preparation method of the modified nano silicon dioxide comprises the following steps: 1) Mix potato starch and sodium hydroxide, add ethanol aqueous solution, stir, heat to 30-40° C., stir, add glycidol under an inert atmosphere, heat to 40-50° C., stir, adjust pH=7-7.5, filter, wash, dry, and crush to obtain modified starch for later use; 2) mixing the modified starch in step 1) with deionized water, stirring to obtain a mixed solution for later use, adding nano-silicon dioxide into the deionized water, ultrasonicating, adding the mixed solution, stirring, filtering, drying, grinding, and obtaining a product for later use; 3) Add the product of step 2) to deionized water, stir, add N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, stir, spray dry, heat at 240-260° C. for 1-3 h, wash, and dry to obtain modified nano-silica.

6. The water-based biodegradable coating according to claim 5, characterized in that: In the step 1), the mass ratio of potato starch to glycidol is 1:(0.1-0.4).

7. The water-based biodegradable coating according to claim 5, characterized in that: In the step 2), the mass ratio of nano silicon dioxide to modified starch is 1:(0.2-0.5).

8. The water-based biodegradable coating according to claim 5, characterized in that: In the step 3), the mass ratio of the product to N-(2-aminoethyl)-3-aminopropyltrimethoxysilane is 1:(0.05-0.3).

9. The water-based biodegradable coating according to claim 1, characterized in that: The defoamer is an organosilicon defoamer.

10. A method for preparing a water-based biodegradable coating according to any one of claims 1 to 9, characterized in that: The following steps are involved: The bio-based resin emulsion and deionized water are mixed, stirred for 10-20 minutes, a defoamer and a leveling agent are added, stirred for 2-5 minutes, a composite filler is added, and stirred for 20-40 minutes to obtain a water-based biodegradable coating.

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