Environment-friendly degradable plastic material and preparation method thereof

Abstract

The application relates to the technical field of plastic materials, and particularly discloses an environment-friendly degradable plastic material and a preparation method thereof. The environment-friendly degradable plastic material comprises the following raw materials in mass fraction: 85-95% of polylactic acid, 5-15% of modified polybutylene adipate terephthalate, 25-35% of plant fiber and 2.2-3.6% of water-resistant emulsion, and the water-resistant emulsion is a boron-based water-resistant emulsion. The environment-friendly degradable plastic material has the advantages that the overall waterproof performance of the environment-friendly degradable plastic can be improved, and the defects that the overall waterproof performance of the environment-friendly degradable plastic is still insufficient are eliminated.

Description

Technical Field

[0001] This application relates to the field of plastic materials technology, and more specifically, to an environmentally friendly biodegradable plastic material and its preparation method. Background Technology

[0002] Traditional plastics, derived from non-renewable fossil fuels such as petroleum, are widely used in various fields due to their low price and lightweight properties. However, the non-degradability of traditional plastic products and their excessive use and improper waste disposal lead to "white pollution," causing significant harm to humans and the ecological environment. Bio-based plastics, on the other hand, are a class of polymer materials derived from biomass resources. They constitute a sustainable plastic manufacturing option. These biomass resources, such as corn sugar, tuber plants, and cellulose, are converted through modern chemical or biological processes. This not only reduces dependence on fossil fuels but also results in relatively low carbon emissions throughout their life cycle. A typical biodegradable plastic is polylactic acid (PLA), which has excellent barrier properties, making it important for applications in food packaging and other fields.

[0003] Plant fibers are widely available, low in cost, low in density, biodegradable, and have good mechanical properties. Combining them with polylactic acid to develop environmentally friendly materials has a reinforcing effect and improves the overall performance of the materials, meeting the requirements of a virtuous cycle of natural resources and promoting sustainable development. However, the cellulose fibrils in plant fibers have natural hydrophilic hydroxyl groups on their surface, which are sensitive to water, making plant fibers unstable in water and potentially reducing the overall waterproof performance of plastic materials. Summary of the Invention

[0004] In order to improve the shortcomings of the overall waterproof performance of environmentally friendly biodegradable plastics, this application provides an environmentally friendly biodegradable plastic material and its preparation method.

[0005] This application provides an environmentally friendly biodegradable plastic material and its preparation method, which adopts the following technical solution:

[0006] In a first aspect, an environmentally friendly biodegradable plastic material comprises the following raw materials by mass fraction: 85-95% polylactic acid, 5-15% modified poly(adipate-butyl terephthalate), 25-35% plant fiber, and 2.2-3.6% water-resistant emulsion, wherein the water-resistant emulsion is a boron-based water-resistant emulsion.

[0007] Since the main component of plant fiber is cellulose, its molecular chain contains a large number of hydroxyl groups, which are very easy to form hydrogen bonds with water molecules, causing the fiber to absorb water and swell. In addition, plant fiber has natural porosity, which increases the surface area in contact with water, further aggravating water absorption. After absorbing water, the interfacial bonding force between the fiber and the plastic matrix decreases.

[0008] Boron-based water-resistant emulsions contain borate esters that can undergo esterification with the hydroxyl groups in cellulose to form stable chemical bonds, thereby reducing the hydrophilicity of the hydroxyl groups. The chemical bonds of borate esters are relatively stable in humid environments, which can delay the hydrolysis process and maintain the waterproof effect for a long time. In addition, the water-resistant emulsion can be uniformly dispersed in polylactic acid and modified poly(adipate-terephthalate-butylene glycolate) to form a continuous hydrophobic network that covers the surface and pores of plant fibers, thereby improving the overall water resistance of plastic materials.

[0009] Preferably, the water-resistant emulsion comprises the following raw materials: 55-59g stearic acid, 100-150ml deionized water, 18-24g diethanolamine, 4.8-9.5ml sodium hydroxide solution, 18-34g isopropanol, 5.8-6.6g boric acid, 90-120ml toluene dehydrating agent, 95-105g liquid rosin, 3-3.74ml potassium hydroxide, and 20-30g pine emulsifier.

[0010] Because the long carbon chain of stearic acid can form a hydrophobic layer through esterification or amidation reactions, effectively blocking water penetration, and can react with diethanolamine to generate stearic acid diethanolamide, it can enhance the interfacial bonding force with plant fibers, reduce fiber water absorption and swelling, and can also introduce polar amide groups to enhance the hydrogen bonding with cellulose hydroxyl groups and enhance interfacial adhesion.

[0011] Preferably, the method for preparing the water-resistant emulsion is as follows:

[0012] Weigh 55-59g of stearic acid granules and place them in a four-necked flask. Add 100-150ml of deionized water and melt at 80-90℃. Then add 18-24g of diethanolamine and 4.8-9.5ml of sodium hydroxide solution and heat at 150-170℃ for 5-7 hours to produce white solid stearic acid diethanolamide.

[0013] Weigh 35-39.6g of stearic acid diethanolamide, add 3-9g of isopropanol and 5.8-6.6g of boric acid, and add 30-50ml of toluene dehydrating agent. Heat the mixture at 110-130℃ for 5-7h to obtain the borate ester / amide complex.

[0014] Weigh 95-105g of melted liquid rosin and pour it into a four-necked flask. Add 15-25g of isopropanol, 3-3.74ml of potassium hydroxide and 60-70ml of toluene dehydrating agent. React at 150-170℃ for 7-9 hours to produce isopropyl rosinate.

[0015] Take 40-48g of borate ester / amide complex and 30-40g of isopropyl rosinate, and react at 110-130℃ until a stable yellow solid is obtained to obtain rosin / stearate borate ester complex.

[0016] Weigh 75-85g of rosin / stearate borate complex and emulsify it with 20-30g of pine emulsifier to obtain a water-resistant emulsion.

[0017] Stearic acid diethanolamide is generated by reacting stearic acid with diethanolamine under alkaline conditions. Its molecule contains both hydrophobic long carbon chains and hydrophilic amide groups, which can serve as an amphiphilic intermediate to enhance the interfacial bonding force with plant fibers and reduce water absorption and swelling. Stearic acid diethanolamide reacts with boric acid to form borate ester bonds, which can block the hydroxyl groups of plant fibers through chemical cross-linking, thus significantly reducing hydrophilicity. Liquid rosin reacts with isopropanol to generate isopropyl abirate. Its abietic acid structure has a rigid hydrophobic skeleton, which can combine with flexible borate ester bonds to form a dense water-resistant layer and block water penetration.

[0018] Preferably, the modified poly(adipate-butyl terephthalate) comprises the following raw materials: 45-55g of poly(adipate-butyl terephthalate), 0.05-0.1g of initiator, and 0.5-1g of modified itaconic anhydride.

[0019] Because modified itaconic anhydride contains anhydride groups, it can combine with poly(adipate-terephthalate-butylene) chains to generate carboxylic acid groups, which helps to enhance the polarity of poly(adipate-terephthalate-butylene) and thus improve its compatibility with polylactic acid and plant fibers.

[0020] Preferably, the modified poly(adipate-terephthalate-butylene) is prepared by weighing 45-55g of poly(adipate-terephthalate-butylene), 0.05-0.1g of initiator and 0.5-1g of modified itaconic anhydride, and blending them in a mixer at 170-190℃ to obtain the modified poly(adipate-terephthalate-butylene).

[0021] Preferably, the modified itaconic anhydride comprises the following raw materials: 9.5-10.1g itaconic anhydride, 5-5.6g diethylene glycol, 9-10.4g calcium acetate, and 10-14g zinc acetate.

[0022] Because the two hydroxyl groups in diethylene glycol can undergo esterification with the anhydride groups of itaconic anhydride to form long chains or cross-linked networks, increasing the molecular weight and inhibiting the thermal motion of molecular chains, and because the calcium ions in calcium acetate and the zinc ions in zinc acetate can form coordination bonds with carboxylic acid groups to construct a rigid metal-organic framework, this is beneficial for improving the thermal stability of plastic materials.

[0023] Preferably, the modified itaconic anhydride is prepared as follows: Weigh 9.5-10.1g of itaconic anhydride, preheat an oil bath, and when the reaction temperature reaches 100-120℃, slowly add 5-5.6g of diethylene glycol to obtain an intermediate product. Weigh 9-10.4g of calcium acetate and 10-14g of zinc acetate and dissolve them in deionized water respectively. Place the intermediate product in an oil bath at 110-130℃, and slowly add the calcium acetate aqueous solution and zinc acetate aqueous solution. Stir the reaction for 2-4 hours, then remove the deionized water by rotary evaporation and remove the byproduct acetic acid by vacuum distillation until no liquid is distilled off to obtain the modified itaconic anhydride.

[0024] Secondly, this application provides a method for preparing an environmentally friendly biodegradable plastic material, employing the following technical solution:

[0025] A method for preparing an environmentally friendly biodegradable plastic material includes the following steps:

[0026] S1: 85-95% polylactic acid and 5-15% modified poly(adipate-terephthalate-butylene) by mass fraction are vacuum dried at 70-90℃ for 10-14h, and then melt-blended to obtain a blend.

[0027] S2: Add 25-35% plant fiber and 2.2-3.6% water-resistant emulsion by mass to the above blend and mix at 130-150℃ for 3-7 minutes using a two-roller plastic mill.

[0028] In summary, this application has the following beneficial effects:

[0029] 1. Since the main component of plant fiber is cellulose, its molecular chain contains a large number of hydroxyl groups, which are very easy to form hydrogen bonds with water molecules, causing the fiber to absorb water and swell. In addition, plant fiber has natural porosity, which increases the surface area in contact with water, further aggravating water absorption. After absorbing water, the interfacial bonding force between the fiber and the plastic matrix decreases.

[0030] Boron-based water-resistant emulsions contain borate esters that can undergo esterification with the hydroxyl groups in cellulose to form stable chemical bonds, thereby reducing the hydrophilicity of the hydroxyl groups. The chemical bonds of borate esters are relatively stable in humid environments, which can delay the hydrolysis process and maintain the waterproof effect for a long time. In addition, the water-resistant emulsion can be uniformly dispersed in polylactic acid and modified poly(adipate-terephthalate-butylene glycolate) to form a continuous hydrophobic network that covers the surface and pores of plant fibers, thereby improving the overall water resistance of plastic materials.

[0031] 2. Because the long carbon chain of stearic acid can form a hydrophobic layer through esterification or amidation reactions, effectively blocking water penetration, and can react with diethanolamine to generate stearic acid diethanolamide, which can enhance the interfacial bonding force with plant fibers, reduce fiber water absorption and swelling, and can also introduce polar amide groups to enhance the hydrogen bonding with cellulose hydroxyl groups and enhance interfacial adhesion.

[0032] 3. Stearic acid diethanolamide is generated by reacting stearic acid with diethanolamine under alkaline conditions. Its molecule contains both hydrophobic long carbon chains and hydrophilic amide groups, which can serve as an amphiphilic intermediate to enhance the interfacial bonding force with plant fibers and reduce water absorption and swelling. Stearic acid diethanolamide reacts with boric acid to form borate ester bonds, which can block the hydroxyl groups of plant fibers through chemical cross-linking, thus significantly reducing hydrophilicity. Liquid rosin reacts with isopropanol to generate isopropyl abirate. Its abietic acid structure is a rigid hydrophobic skeleton, which can combine with flexible borate ester bonds to form a dense water-resistant layer and block water penetration. Detailed Implementation

[0033] The present application will be further described in detail below with reference to Examples 1-10 and Comparative Examples 1-2.

[0034] raw material

[0035] Polylactic acid CAS: 31852-84-3; Ramie fiber Hunan Huasheng Dongting Hemp Industry Co., Ltd.; Stearic acid CAS: 57-11-4; Deionized water CAS: 7732-18-5; Diethanolamine CAS: 111-42-2; Sodium hydroxide CAS: 1310-73-2; Isopropanol CAS: 67-63-0; Boric acid CAS: 10043-35-3; Toluene CAS: 108-88-3; Rosin Weifang Huapu Chemical Co., Ltd.; Hydroxide Potassium CAS: 1310-58-3; Pine emulsifier Weifang Huapu Chemical Co., Ltd.; Poly(butylene adipate-terephthalate) ester Xinjiang Lanshan Tunhe Technology Co., Ltd.; Initiator 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane Shanghai Aladdin Biochemical Technology Co., Ltd.; Itaconic anhydride CAS: 2170-03-8; Diethylene glycol CAS: 110-99-6; Calcium acetate CAS: 62-54-4; Zinc acetate CAS: 557-34-6. Example 1

[0036] An environmentally friendly biodegradable plastic material comprises the following raw materials by mass fraction: 90% polylactic acid, 10% modified poly(butylene adipate-terephthalate), 30% plant fiber, and 2.9% water-resistant emulsion.

[0037] Specifically, the preparation method of environmentally friendly biodegradable plastic materials includes the following steps:

[0038] S1: Weigh 9.8g of itaconic anhydride, preheat an oil bath, and when the reaction temperature reaches 110℃, slowly add 5.3g of diethylene glycol to obtain an intermediate product. Weigh 9.7g of calcium acetate and 12g of zinc acetate and dissolve them in deionized water. Place the intermediate product in an oil bath at 120℃, and slowly add the calcium acetate aqueous solution and zinc acetate aqueous solution. Stir the reaction for 3 hours, then remove the deionized water by rotary evaporation and remove the byproduct acetic acid by vacuum distillation until no liquid is distilled out to obtain the modified itaconic anhydride.

[0039] S2: Weigh 50g of poly(butylene adipate-terephthalate), 0.075g of 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane and 0.75g of modified itaconic anhydride, and blend them in a mixer at 180℃ to obtain modified poly(butylene adipate-terephthalate);

[0040] S3: Weigh 57g of stearic acid granules and place them in a four-necked flask. Add 130ml of deionized water and melt at 85℃. Then add 21g of diethanolamine and 7.15ml of 5% sodium hydroxide solution and heat at 160℃ for 6 hours to produce white solid stearic acid diethanolamide.

[0041] S4: Weigh 37.3g of stearic acid diethanolamide, add 6g of isopropanol and 6.2g of boric acid, and add 40ml of toluene dehydrating agent. Heat the mixture at 120℃ for 6h to obtain the borate ester / amide complex.

[0042] S5: Weigh 100g of melted liquid rosin and pour it into a four-necked flask. Add 20g of isopropanol, 3.37ml of 5% potassium hydroxide catalyst and 65ml of toluene dehydrating agent. React at 160℃ for 8 hours to produce isopropyl rosinate.

[0043] S6: Take 44g of borate ester / amide complex and 35g of isopropyl rosinate, and react them at 120℃ until a stable yellow solid is obtained to obtain rosin / stearate borate ester complex.

[0044] S7: Weigh 80g of rosin / stearate borate complex and emulsify it with 25g of pine emulsifier to obtain a water-resistant emulsion;

[0045] S8: 90% polylactic acid and 10% modified poly(adipate-terephthalate-butylene) by mass fraction were vacuum dried at 80°C for 12 h, and then melt-blended to obtain a blend.

[0046] S9: Add 30% plant fiber and 2.9% water-resistant emulsion by mass to the above blend, and mix at 140°C for 5 minutes using a two-roller plastic mill to obtain an environmentally friendly biodegradable plastic material.

[0047] Example 2-Example 3

[0048] The difference from Example 1 is that the mass fraction of each component added to the environmentally friendly biodegradable plastic material is different, as shown in Table 1.

[0049] Table 1. Mass fraction (%) of each component added to the environmentally friendly biodegradable plastic materials in Examples 1-3

[0050] Example 1 Example 2 Example 3 Polylactic acid 90 85 95 Modified poly(adipate-terephthalate-butylene) 10 15 5 plant fiber 30 35 25 Water-resistant emulsion 2.9 2.2 3.6 Example 4

[0051] The difference from Example 1 is that the modified poly(adipate-butyl terephthalate) is replaced with an equal amount of poly(adipate-butyl terephthalate).

[0052] Examples 5-6

[0053] The difference from Example 1 is that the amount of each component added to the modified poly(adipate-terephthalate-butylene) is different, as shown in Table 2.

[0054] Table 2. Amounts (g) of each component added in modified poly(adipate-terephthalic acid-butylene glycolate) in Examples 1 and 5-6.

[0055] Example 1 Example 5 Example 6 Poly(butylene adipate) terephthalate 50 45 55 2,5-Dimethyl-2,5-bis(tert-butylperoxy)hexane 0.075 0.1 0.05 Modified itaconic anhydride 0.75 1 0.5

[0056] Examples 7-8

[0057] The difference from Example 1 is that the amount of each component added in the modified itaconic anhydride is different, as shown in Table 3.

[0058] Table 3. Amounts (g) of each component added in modified itaconic anhydride in Examples 1 and 7-8.

[0059] Example 1 Example 7 Example 8 Itaconic anhydride 9.8 10.1 9.5 Diethylene glycol 5.3 5 5.6 Calcium acetate 9.7 9 10.4 Zinc acetate 12 14 10

[0060] Examples 9-10

[0061] The difference from Example 1 is that the amount of each component added in the water-resistant emulsion is different, as shown in Table 4.

[0062] Table 4. Amounts of each component added to the water-resistant emulsion in Examples 1 and 9-10

[0063] Example 1 Example 9 Example 10 stearic acid 57g 55g 59g Deionized water 130ml 150ml 100ml diethanolamine 21g 18g 24g Sodium hydroxide solution 7.15ml 4.8ml 9.5ml Isopropanol 26g 18g 34g boric acid 6.2g 6.6g 5.8g Toluene dehydrating agent 105ml 90ml 120ml Liquid rosin 100g 105g 95g potassium hydroxide 3.37ml 3ml 3.74ml Pine emulsifier 25g 20g 30g

[0064] Comparative Example 1

[0065] The difference from Example 1 is that no water-resistant emulsion is added.

[0066] Comparative Example 2

[0067] The difference from Example 1 is that the modified itaconic anhydride was replaced with an equal amount of itaconic anhydride.

[0068] Performance testing

[0069] I. Waterproof performance

[0070] Three samples were taken from Examples 1-10 and Comparative Examples 1-2 respectively and extruded into films. The waterproof performance of the samples was tested according to GB / T 1037-2021 "Determination of Water Vapor Permeability of Plastic Films and Sheets by Cup Weight Gain and Weight Loss Method".

[0071] The test data is shown in Table 5.

[0072] Table 5. Waterproofing performance test results of Examples 1-10 and Comparative Examples 1-2

[0073] <![CDATA[Water vapor transmission rate g / (m 2 ·24 h)]]> Example 1 12 Example 2 18 Example 3 15 Example 4 36 Example 5 14 Example 6 16 Example 7 13 Example 8 17 Example 9 20 Example 10 19 Comparative Example 1 68 Comparative Example 2 25

[0074] II. Thermal stability performance

[0075] Three samples were taken from Examples 1-10 and Comparative Example 1 and pressed into thin sheets. The sheets were placed in a thermal aging test chamber and heated at a constant temperature of 180°C. Samples were taken every 10 minutes to observe the color change of the samples. The time when the samples turned black was recorded as the static aging test change time, and the average value was taken.

[0076] The test data is shown in Table 6.

[0077] Table 6. Thermal stability test results of Examples 1-10 and Comparative Examples 1-2

[0078] Static aging test variation time (min) Example 1 115 Example 2 100 Example 3 105 Example 4 50 Example 5 110 Example 6 112 Example 7 113 Example 8 111 Example 9 108 Example 10 106 Comparative Example 1 90 Comparative Example 2 60

[0079] Combining Example 1 and Comparative Example 1 with Tables 5 and 6, it can be seen that, compared with Example 1, the water vapor permeability of Comparative Example 1 is significantly increased, and the change time in the static aging test of Comparative Example 1 is shortened. This shows that, compared with not adding water-resistant emulsion, adding water-resistant emulsion affects the thermal stability of plastic materials and can effectively improve the waterproof performance of plastic materials.

[0080] The reason for this is that the borate esters in boron-based water-resistant emulsions can undergo esterification with the hydroxyl groups in cellulose to form stable chemical bonds, thereby reducing the hydrophilicity of the hydroxyl groups. The chemical bonds of borate esters are relatively stable in humid environments, which can delay the hydrolysis process and maintain the waterproof effect for a long time. In addition, the water-resistant emulsion can be uniformly dispersed in polylactic acid and modified poly(adipate-terephthalate-butylene glycolate) to form a continuous hydrophobic network that covers the surface and pores of plant fibers, thereby improving the overall water resistance of plastic materials.

[0081] Stearic acid reacts with diethanolamine under alkaline conditions to form stearic acid diethanolamide. Its molecule contains both hydrophobic long carbon chains and hydrophilic amide groups, which can act as an amphiphilic intermediate to enhance the interfacial bonding force with plant fibers and reduce water absorption and swelling. Stearic acid diethanolamide reacts with boric acid to form borate ester bonds, which can block the hydroxyl groups of plant fibers through chemical cross-linking and significantly reduce hydrophilicity. Liquid rosin reacts with isopropanol to form isopropyl abirate. Its abietic acid structure is a rigid hydrophobic skeleton, which can combine with flexible borate ester bonds to form a dense water-resistant layer and block water penetration.

[0082] Combining Example 1 and Comparative Example 2 with Tables 5 and 6, it can be seen that, compared with Example 1, the water vapor permeability of Comparative Example 2 is increased, and the static aging test change time of Comparative Example 2 is significantly shortened. This shows that, compared with adding conventional itaconic anhydride, adding modified itaconic anhydride can effectively improve the waterproof performance and thermal stability of plastic materials.

[0083] The reason for this is that the two hydroxyl groups in diethylene glycol can undergo esterification with the anhydride groups of itaconic anhydride to form long chains or cross-linked networks, increasing the molecular weight and inhibiting the thermal motion of molecular chains. The calcium ions in calcium acetate and the zinc ions in zinc acetate can form coordinate bonds with carboxylic acid groups to construct a rigid metal-organic framework, which is beneficial to improving the thermal stability of plastic materials.

[0084] Combining Examples 1 and 2-3 with Tables 5 and 6, it can be seen that, compared with Example 1, the water vapor permeability of Examples 2 and 3 is increased, and the static aging test change time of Examples 2 and 3 is slightly shortened. This indicates that the mass fraction of each component added to the environmentally friendly biodegradable plastic material affects the waterproof performance and thermal stability of the plastic material, and the mass fraction of each component added to the environmentally friendly biodegradable plastic material in Example 1 is optimal.

[0085] Combining Examples 1 and 4 with Tables 5 and 6, it can be seen that, compared with Example 1, the water vapor permeability of Example 4 is significantly increased, and the static aging test change time of Example 4 is significantly shortened. This indicates that, compared with the addition of conventional poly(adipate-terephthalate-butylene), the addition of modified poly(adipate-terephthalate-butylene) can effectively improve the waterproof performance and thermal stability of plastic materials.

[0086] The reason for this is that modified itaconic anhydride contains anhydride groups, which can combine with poly(adipate-terephthalate-butylene) chains to generate carboxylic acid groups. This helps to enhance the polarity of poly(adipate-terephthalate-butylene), thereby improving its compatibility with polylactic acid and plant fibers.

[0087] Combining Examples 1 and 5-6 with Tables 5 and 6, it can be seen that, compared to Example 1, the water vapor permeability of Examples 5 and 6 is increased, and the static aging test change time of Examples 5 and 6 is shortened. This indicates that the amount of each component added to the modified poly(adipate-terephthalate-butylene) affects the waterproof performance and thermal stability of the plastic material, and the amount of each component added to the modified poly(adipate-terephthalate-butylene) in Example 1 is optimal.

[0088] Combining Examples 1 and 7-8 with Tables 5 and 6, it can be seen that, compared with Example 1, the water vapor permeability of Examples 7 and 8 is increased, and the static aging test change time of Examples 7 and 8 is shortened. This indicates that the amount of each component of modified itaconic anhydride added affects the waterproof performance and thermal stability of the plastic material, and the amount of each component of modified itaconic anhydride added in Example 1 is optimal.

[0089] Combining Examples 1 and 9-10 with Tables 5 and 6, it can be seen that, compared with Example 1, the water vapor permeability of Examples 9 and 10 is increased, and the static aging test change time of Examples 9 and 10 is shortened. This indicates that the amount of each component added to the water-resistant emulsion affects the waterproof performance of the plastic material, and the amount of each component added to the water-resistant emulsion in Example 1 is optimal.

[0090] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. An environmentally friendly biodegradable plastic material, characterized in that, The raw materials include the following components by mass fraction: 85-95% polylactic acid, 5-15% modified poly(adipate-terephthalate-butylene glycol), 25-35% plant fiber, and 2.2-3.6% water-resistant emulsion, wherein the water-resistant emulsion is a boron-based water-resistant emulsion. The water-resistant emulsion comprises the following raw materials: 55-59g stearic acid, 100-150ml deionized water, 18-24g diethanolamine, 4.8-9.5ml sodium hydroxide solution, 18-34g isopropanol, 5.8-6.6g boric acid, 90-120ml toluene dehydrating agent, 95-105g liquid rosin, 3-3.74ml potassium hydroxide, and 20-30g pine emulsifier; The modified poly(adipate-terephthalate-butylene) comprises the following raw materials: 45-55g of poly(adipate-terephthalate-butylene), 0.05-0.1g of initiator, and 0.5-1g of modified itaconic anhydride; The modified itaconic anhydride comprises the following raw materials: 9.5-10.1g itaconic anhydride, 5-5.6g diethylene glycol, 9-10.4g calcium acetate, and 10-14g zinc acetate.

2. The environmentally friendly biodegradable plastic material according to claim 1, characterized in that, The preparation method of the water-resistant emulsion is as follows: Weigh 55-59g of stearic acid granules and place them in a four-necked flask. Add 100-150ml of deionized water and melt at 80-90℃. Then add 18-24g of diethanolamine and 4.8-9.5ml of sodium hydroxide solution. Heat at 150-170℃ for 5-7 hours to generate a white solid stearic acid diethanolamide. Weigh 35-39.6g of stearic acid diethanolamide, add 3-9g of isopropanol and 5.8-6.6g of boric acid, and add 30-50ml of toluene dehydrating agent. Heat at 110-130℃ for 5-7 hours to obtain a borate ester / amide complex. To prepare a rosin / stearate borate complex, weigh 95-105g of melted liquid rosin and pour it into a four-necked flask. Add 15-25g of isopropanol, 3-3.74ml of potassium hydroxide, and 60-70ml of toluene as a dehydrating agent. React at 150-170℃ for 7-9 hours to produce isopropyl rosinate. Take 40-48g of the borate / amide complex and 30-40g of isopropyl rosinate and react at 110-130℃ until a stable yellow solid is obtained to yield a rosin / stearate borate complex. Weigh 75-85g of the rosin / stearate borate complex and emulsify it with 20-30g of pine resin emulsifier to obtain a water-resistant emulsion.

3. The environmentally friendly biodegradable plastic material according to claim 1, characterized in that, The modified poly(adipate-terephthalate-butylene) is prepared by weighing 45-55g of poly(adipate-terephthalate-butylene), 0.05-0.1g of initiator and 0.5-1g of modified itaconic anhydride, and mixing them in a mixer at 170-190℃ to obtain the modified poly(adipate-terephthalate-butylene).

4. The environmentally friendly biodegradable plastic material according to claim 1, characterized in that, The preparation method of the modified itaconic anhydride is as follows: Weigh 9.5-10.1g of itaconic anhydride, preheat an oil bath, and when the reaction temperature rises to 100-120℃, slowly add 5-5.6g of diethylene glycol to obtain an intermediate product. Weigh 9-10.4g of calcium acetate and 10-14g of zinc acetate and dissolve them in deionized water respectively. Place the intermediate product in an oil bath at 110-130℃, and slowly add the calcium acetate aqueous solution and zinc acetate aqueous solution. Stir the reaction for 2-4 hours, then remove the deionized water by rotary evaporation and remove the byproduct acetic acid by vacuum distillation until no liquid is distilled out to obtain the modified itaconic anhydride.

5. A method for preparing an environmentally friendly biodegradable plastic material according to any one of claims 1-4, characterized in that, Includes the following steps: S1: 85-95% polylactic acid and 5-15% modified poly(adipate-terephthalate-butylene) by mass fraction are vacuum dried at 70-90℃ for 10-14h, and then melt-blended to obtain a blend. S2: Add 25-35% plant fiber and 2.2-3.6% water-resistant emulsion by mass to the above blend and mix at 130-150℃ for 3-7 minutes using a two-roller plastic mill.