A plant-based modified packaging material and a method of making the same

Abstract

This invention discloses a plant-based modified packaging material and its preparation method, relating to the field of packaging material technology. In preparing the plant-based modified packaging material, this invention uses a double-bonded silane coupling agent to treat sheet-like zinc oxide nanoparticles to obtain double-bonded sheet-like zinc oxide nanoparticles; tung oil is oxidized with hydrogen peroxide, ring-opened with hydrochloric acid, and quaternized with triethylamine to obtain tung oil quaternary ammonium salt; the double-bonded sheet-like zinc oxide nanoparticles, tung oil quaternary ammonium salt, polylactic acid, and dichloromethane are mixed and dried in a mold to form a plant-based modified film substrate, which is then impregnated with a double-bonded crosslinking agent and a free radical initiator to obtain the plant-based modified packaging material. The plant-based modified packaging material prepared by this invention has excellent water vapor barrier effect and long-lasting antibacterial effect.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, specifically to a plant-based modified packaging material and its preparation method. Background Technology

[0002] Against the backdrop of steady economic growth and increasing public awareness of environmental protection, traditional petroleum-based plastic products can no longer meet the demands of green and low-carbon development. Polylactic acid (PLA), as a fully biodegradable polymer material prepared from agricultural and forestry resources such as corn and straw, has become a research focus in the field of environmentally friendly materials. However, the poor mechanical properties, water vapor barrier properties, and lack of antibacterial functions of pure PLA are the main bottlenecks restricting its industrialization and promotion.

[0003] Conventional synthetic toughening and plasticizing agents, as well as some small-molecule antibacterial agents, are prone to migration and loss, posing ecological pollution and biotoxicity problems, which are inconsistent with the development trend of green materials. Currently, the industry has shifted towards biomass-based environmentally friendly additives such as citric acid and modified vegetable oils. Tung oil, as a typical agricultural and forestry biomass resource, has abundant reserves, excellent chemical activity, and also possesses natural antibacterial activity. Utilizing tung oil to toughen and antibacterial PLA can effectively improve the overall performance of polylactic acid. Further application of zinc, which is harmless to the human body, can further enhance the antibacterial and barrier effects, providing new technical ideas for the functionalization and diversified application of PLA. Summary of the Invention

[0004] The purpose of this invention is to provide a plant-based modified packaging material and its preparation method to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A plant-based modified packaging material is prepared by mixing double-bonded flake-shaped nano zinc oxide, tung oil quaternary ammonium salt, polylactic acid and dichloromethane, drying them in a mold to form a plant-based modified film substrate, and then impregnating it with an impregnation solution.

[0006] As an optimization, the double-bonded sheet-like zinc oxide nanoparticles are prepared by treating sheet-like zinc oxide nanoparticles with a double-bonded silane coupling agent.

[0007] As an optimization, the tung oil quaternary ammonium salt is prepared by oxidizing tung oil to epoxidized tung oil with hydrogen peroxide, reacting it with hydrochloric acid, and finally reacting it with triethylamine.

[0008] As an optimization, the impregnation solution is a mixture of ethylene glycol diacrylate, benzoyl peroxide, and anhydrous ethanol.

[0009] A method for preparing a plant-based modified packaging material includes the following preparation steps: (1) Zinc nitrate hexahydrate, oleic acid, and deionized water are mixed evenly in a mass ratio of 1:(0.3~0.4):(60~70), and then urea with a molar amount of 30~40 times that of zinc nitrate hexahydrate is added. The mixture is placed in a sealed container and reacted at 130~140℃ for more than 12 hours. After cooling to room temperature, the mixture is centrifuged, washed and dried, and then calcined in a muffle furnace at 400~450℃ for more than 2 hours to obtain sheet-like nano zinc oxide. (2) Double-bonded sheet-like zinc oxide was prepared by treating sheet-like zinc oxide with a double-bonded silane coupling agent; (3) Mix tung oil and epoxidation catalyst at a mass ratio of 1:(0.03~0.04) evenly, then add 0.6~0.7 times the mass of tung oil in a 30% hydrogen peroxide solution, stir at 40~45℃ for 30~40 min, wash, dry, and rotary evaporate to obtain epoxidized tung oil; mix epoxidized tung oil and acetone at a mass ratio of 1:3 evenly, and under stirring at 40~45℃, add an equal mass of 0.1mol / L hydrochloric acid solution of epoxidized tung oil at a uniform rate within 2 h, wash with pure water and ethyl acetate until pH is neutral, take the upper organic phase, dry, and rotary evaporate to obtain chlorinated tung oil; mix chlorinated tung oil, triethylamine and tetrahydrofuran at a mass ratio of 1:(0.5~0.6):(40~50) evenly, react at 50℃ for more than 48 h, remove tetrahydrofuran and excess triethylamine by evaporation to obtain tung oil quaternary ammonium salt; (4) Weigh 0.5%~5% of double-bonded sheet-like nano zinc oxide, 0.5%~9% of tung oil quaternary ammonium salt, and the remainder is polylactic acid. Mix the double-bonded sheet-like nano zinc oxide, tung oil quaternary ammonium salt, polylactic acid and dichloromethane in a mold and dry them to form a plant-based modified film substrate. (5) Mix the double bond crosslinking agent, free radical initiator and anhydrous ethanol to form an impregnation solution; immerse the plant-based modified film substrate in the impregnation solution, remove it and drain until no liquid drips, let it stand in an oven at 60~70℃ for 2~3 minutes, then put it in the impregnation solution for 5~10 seconds and remove it directly, drain until no liquid drips, let it stand in an oven at 160~170℃ for 3 minutes, wash it with pure water, and dry it to obtain the plant-based modified packaging material.

[0010] As an optimization, the sheet-like nano zinc oxide described in step (1) can be commercially available or prepared by referring to existing technologies. As an optimization, the double-bonded silane coupling agent in step (2) is one or a mixture of A-151, A-171, A-172 and KH570.

[0011] As an optimization, the method of treating sheet-like nano zinc oxide with the double-bonded silane coupling agent described in step (2) can refer to the application guidelines for the corresponding silane coupling agent or to existing technologies.

[0012] As an optimization, the preparation method of double-bonded sheet-like zinc oxide in step (2) is as follows: Silane coupling agent KH570, pure water and anhydrous ethanol are mixed evenly in a mass ratio of 1:2:5~7, the pH is adjusted to 5 with 0.1mol / L hydrochloric acid, and stirred at room temperature for 8~10min to obtain silane treatment solution. The sheet-like zinc oxide and anhydrous ethanol are mixed in a mass ratio of 1:8~10 and ultrasonically dispersed for 20~30min to obtain sheet-like zinc oxide dispersion. The sheet-like zinc oxide dispersion and silane treatment solution are mixed in equal volumes, ultrasonically dispersed for 30~40min, centrifuged, washed with pure water, and dried to obtain double-bonded sheet-like zinc oxide.

[0013] As an optimization, the epoxidation catalyst in step (3) is one or a mixture of molybdic acid, tungstic acid, phosphotungstic acid, molybdic acid peroxide complex, tungstic acid peroxide complex and phosphotungstic acid peroxide complex.

[0014] As an optimization, the double bond crosslinking agent in step (5) is one or a mixture of divinylbenzene, N,N'-methylenebisacrylamide, trimethylolpropane triacrylate, ethylene glycol diacrylate, 1,4-butanediol diacrylate and 1,6-hexanediol diacrylate.

[0015] As an optimization, the free radical initiator in step (5) is one or more of azobisisobutyronitrile, benzoyl peroxide, potassium persulfate, and ammonium persulfate.

[0016] Compared with the prior art, the beneficial effects achieved by the present invention are: In preparing plant-based modified packaging materials, this invention uses hydrogen peroxide to oxidize tung oil into epoxidized tung oil, then reacts it with hydrochloric acid, and finally reacts it with triethylamine to obtain tung oil quaternary ammonium salt; double-bonded sheet-like nano zinc oxide, tung oil quaternary ammonium salt, polylactic acid and dichloromethane are mixed and placed in a mold and dried to form a plant-based modified film substrate, which is then impregnated with a double-bonded crosslinking agent and a free radical initiator to obtain the final product.

[0017] First, zinc nitrate hexahydrate, oleic acid, deionized water, and urea are mixed and subjected to a hydrothermal reaction. During the growth of zinc oxide crystal nuclei, oleic acid molecules preferentially adsorb onto specific crystal faces, causing the crystal nuclei to grow along the adsorbed crystal faces. Due to anisotropic growth, a plate-like morphology is formed. Using plate-like nano-zinc oxide can effectively improve barrier performance and also exert the bactericidal properties of zinc ions. Double-bonded plate-like nano-zinc oxide is prepared by treating the plate-like nano-zinc oxide with a double-bonded silane coupling agent. Modification with the double-bonded silane coupling agent can improve the aggregation phenomenon of plate-like nano-zinc oxide and the problem of poor organic-inorganic interface bonding. At the same time, the surface double bonds can participate in subsequent polymerization, thereby improving the gas barrier effect.

[0018] Secondly, the tung oil quaternary ammonium salt and polylactic acid raw materials used in this invention are green and environmentally friendly. The unreacted double bonds and active hydrogen sites on the tung oil quaternary ammonium salt can participate in the cross-linking grafting of the double bonds, improve the cross-linking effect, thereby improving the gas barrier effect and having a contact sterilization effect. Compared with the traditional method of adding antibacterial agents, the sterilization effect is long-lasting and effective. In addition, the zinc ions released by the double bonded sheet-like nano zinc oxide further expand the sterilization range.

[0019] Finally, when impregnating with double bond crosslinking agent and free radical initiator, ensure thorough impregnation so that the double bond crosslinking agent and free radical initiator completely penetrate the pore defects, crosslinking to repair the pore defects, and further improve the gas barrier effect. Crosslinking also increases tensile strength. The mechanism is similar to improving the gas barrier effect and will not be described again. Detailed Implementation

[0020] 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.

[0021] To more clearly illustrate the method provided by the present invention, the following embodiments will be described in detail.

[0022] The raw materials used in each embodiment and comparative example are as follows; unless otherwise specified, they are all common pure substances. Tung oil, industrial grade, Shandong Tongxin Chemical Co., Ltd. Polylactic acid, REVODE110, Zhejiang Hisun Biomaterials Co., Ltd.; Zinc oxide nanoparticles, 95%+, Xi'an Qiyue Biotechnology Co., Ltd. The epoxidation catalyst is phosphotungstic acid.

[0023] Example 1:

[0024] A method for preparing a plant-based modified packaging material mainly includes the following preparation steps: (1) Zinc nitrate hexahydrate, oleic acid, and deionized water were mixed evenly at a mass ratio of 1:0.3:60 and stirred at room temperature until completely dissolved. Then, urea with a molar amount of 30 times that of zinc nitrate hexahydrate was added, and the mixture was placed in a sealed container and reacted at 140°C for 20 h. After cooling to room temperature, the mixture was centrifuged and washed three times each with pure water and anhydrous ethanol. The mixture was dried at 70°C for 8 h and calcined in a muffle furnace at 400°C for 2 h to obtain sheet-like nano zinc oxide. (2) Mix silane coupling agent KH570, pure water and anhydrous ethanol at a mass ratio of 1:2:5. Adjust the pH to 5 with 0.1 mol / L hydrochloric acid and stir at room temperature for 10 min to obtain silane treatment solution. Mix flaky nano zinc oxide and anhydrous ethanol at a mass ratio of 1:8 and ultrasonically disperse for 30 min to obtain flaky nano zinc oxide dispersion. Mix the flaky nano zinc oxide dispersion and silane treatment solution in equal volumes, continue ultrasonication for 40 min, centrifuge, wash with pure water, and dry to obtain double bonded flaky nano zinc oxide. (3) Mix tung oil and epoxidation catalyst at a mass ratio of 1:0.03, then add 0.6 times the mass of tung oil in a 30% hydrogen peroxide solution. Stir at 40°C for 30 min, wash with a mixture of pure water and ethyl acetate at a ratio of 1:3, take the upper organic phase, dry, and rotary evaporate to obtain epoxidized tung oil. Mix epoxidized tung oil and acetone at a mass ratio of 1:3, and add an equal mass of 0.1 mol / L hydrochloric acid solution to epoxidized tung oil at a constant rate over 2 h under stirring at 40°C. Wash repeatedly with a mixture of pure water and ethyl acetate at a ratio of 1:3 until the pH is neutral. Take the upper organic phase, dry, and rotary evaporate to obtain chlorinated tung oil. Mix chlorinated tung oil, triethylamine, and tetrahydrofuran at a mass ratio of 1:0.5:40~50, react at 50°C for 72 h, and remove tetrahydrofuran and excess triethylamine to obtain tung oil quaternary ammonium salt. (4) Weigh 2% of double-bonded sheet-like nano zinc oxide, 3% of tung oil quaternary ammonium salt, and the remainder is polylactic acid according to the mass fraction. Place each weighed component in dichloromethane at 20 times the mass of polylactic acid and stir for 3 hours. After the reaction is completed, pour the mixture into a flat mold and dry at room temperature for 48 hours to obtain the plant-based modified film substrate. (5) Ethylene glycol diacrylate, benzoyl peroxide and anhydrous ethanol are mixed evenly in a mass ratio of 1:0.1:50 to prepare an impregnation solution; the plant-based modified film substrate is placed in the impregnation solution and impregnated at 20°C for 20 min, taken out and drained until no liquid drips in 10 s, placed in an oven at 60°C for 2 min, placed in the impregnation solution for 10 s and taken out directly, drained until no liquid drips in 10 s, placed in an oven at 160°C for 3 min, rinsed with pure water 3 times, and dried to obtain the plant-based modified packaging material.

[0025] Example 2:

[0026] The only difference between Example 2 and Example 1 is that "2% double-bonded sheet-like nano zinc oxide" in step (4) is changed to "0.5% double-bonded sheet-like nano zinc oxide". The rest of the steps are the same as in Example 1.

[0027] Example 3:

[0028] The only difference between Example 3 and Example 1 is that "2% of double-bonded sheet-like nano zinc oxide" in step (4) is changed to "1% of double-bonded sheet-like nano zinc oxide". The rest of the steps are the same as in Example 1.

[0029] Example 4:

[0030] The only difference between Example 4 and Example 1 is that "2% double-bonded sheet-like nano zinc oxide" in step (4) is changed to "3% double-bonded sheet-like nano zinc oxide", and the other steps are the same as in Example 1.

[0031] Example 5:

[0032] The only difference between Example 5 and Example 1 is that "2% double-bonded sheet-like nano zinc oxide" in step (4) is changed to "5% double-bonded sheet-like nano zinc oxide", and the other steps are the same as in Example 1.

[0033] Example 6:

[0034] The only difference between Example 6 and Example 1 is that “3% tung oil quaternary ammonium salt” in step (4) is changed to “0.5% tung oil quaternary ammonium salt”, and the rest of the steps are the same as in Example 1.

[0035] Example 7:

[0036] The only difference between Example 7 and Example 1 is that “3% tung oil quaternary ammonium salt” in step (4) is changed to “1% tung oil quaternary ammonium salt”, and the rest of the steps are the same as in Example 1.

[0037] Example 8:

[0038] The only difference between Example 8 and Example 1 is that “3% tung oil quaternary ammonium salt” in step (4) is changed to “2% tung oil quaternary ammonium salt”, and the rest of the steps are the same as in Example 1.

[0039] Example 9:

[0040] The only difference between Example 9 and Example 1 is that “3% tung oil quaternary ammonium salt” in step (4) is changed to “5% tung oil quaternary ammonium salt”, and the rest of the steps are the same as in Example 1.

[0041] Example 10:

[0042] The only difference between Example 10 and Example 1 is that “3% tung oil quaternary ammonium salt” in step (4) is changed to “9% tung oil quaternary ammonium salt”, and the rest of the steps are the same as in Example 1.

[0043] Comparative Example 1: The only difference between Comparative Example 1 and Example 1 is that “zinc oxide nanoparticles” are used instead of “double-bonded sheet-like zinc oxide nanoparticles”. The remaining steps are the same as in Example 1.

[0044] Comparative Example 2: The only difference between Comparative Example 2 and Example 1 is that step (2) is omitted, and “sheet-shaped nano zinc oxide” is directly used in subsequent steps. The remaining steps are the same as in Example 1.

[0045] Comparative Example 3: The only difference between Comparative Example 3 and Example 1 is that step (5) is omitted; the remaining steps are the same as in Example 1.

[0046] Comparative Example 4: Step (5) of Comparative Example 4 is as follows: Benzoyl peroxide and anhydrous ethanol are mixed evenly at a mass ratio of 0.1:50 to prepare an impregnation solution; the plant-based modified film substrate is placed in the impregnation solution and impregnated at 20°C for 20 min; it is then removed, drained until no liquid drips after 10 s, placed in an oven at 60°C for 2 min, placed in the impregnation solution again for 10 s, removed directly, drained until no liquid drips after 10 s, placed in an oven at 160°C for 3 min, rinsed 3 times with pure water, and dried to obtain the plant-based modified packaging material. The remaining steps are the same as in Example 1.

[0047] Comparative Example 5: Step (5) of Comparative Example 5 is as follows: ethylene glycol diacrylate, benzoyl peroxide, and anhydrous ethanol are mixed evenly at a mass ratio of 1:0.1:50 to prepare an impregnation solution; the plant-based modified film substrate is placed in the impregnation solution and impregnated at 20°C for 10 seconds, then removed and drained until no liquid drips after 10 seconds, placed in a 60°C oven for 2 minutes, then placed in the impregnation solution for 10 seconds and removed directly, drained until no liquid drips after 10 seconds, placed in a 160°C oven for 3 minutes, rinsed three times with pure water, and dried to obtain the plant-based modified packaging material. The remaining steps are the same as in Example 1.

[0048] Comparative Example 6: The difference between Comparative Example 6 and Example 1 is that step (4) is different from that of Example 1 only in that “2% of double-bonded sheet-like nano zinc oxide” in step (4) is changed to “0% of double-bonded sheet-like nano zinc oxide”, and the rest of the steps are the same as in Example 1.

[0049] Comparative Example 7: The only difference between Comparative Example 7 and Example 1 is that “3% tung oil quaternary ammonium salt” in step (4) is changed to “0% tung oil quaternary ammonium salt”, and the rest of the steps are the same as in Example 1.

[0050] Comparative Example 8: A method for preparing a plant-based modified packaging material mainly includes the following preparation steps: (1) Weigh 2% tung oil, 1% dodecyltrimethylammonium chloride, and the remainder polylactic acid according to the mass fraction. Place each weighed component in dichloromethane at 20-25 times the mass of polylactic acid and stir for 3 hours. After the reaction is completed, pour the mixture into a flat mold and dry at room temperature for 48 hours to obtain the plant-based modified film substrate. (2) Ethylene glycol diacrylate, benzoyl peroxide and anhydrous ethanol are mixed evenly in a mass ratio of 1:0.1:50 to prepare an impregnation solution; the plant-based modified film substrate is placed in the impregnation solution and impregnated at 20°C for 10s, taken out and drained until no liquid drips after 10s, placed in an oven at 60°C for 2min, placed in the impregnation solution for 10s and taken out directly, drained until no liquid drips after 10s, placed in an oven at 160°C for 3min, rinsed with pure water 3 times, and dried to obtain the plant-based modified packaging material.

[0051] Test Example 1: Gas barrier effect test Test method: The water vapor transmission rate of the plant-based modified packaging material was measured using a water vapor transmission rate tester according to ASTM D1653 standard. The test sample was a film with a diameter of 10 cm and a thickness of 0.1 mm. The results are shown in Table 1.

[0052] Table 1 A comparison of the experimental data in Table 1 shows that the plant-based modified packaging material prepared by this invention has a good water vapor barrier effect.

[0053] Comparison of Examples 1-9 shows that when the proportion of double-bonded sheet-like nano zinc oxide reaches 2%, the subsequent changes are very small. Considering that adding too many nanoparticles will lead to a decrease in flexibility and an increase in cost, 2% is the optimal choice. When the proportion of tung oil quaternary ammonium salt reaches 3%, the water vapor transmission rate remains basically unchanged, so 3% is the optimal choice.

[0054] As can be seen from the comparison with Comparative Example 1, the sheet-like two-dimensional structure has a better barrier effect than ordinary nanoparticles.

[0055] By comparing with Comparative Example 2, it can be found that modification with double-bonded silane coupling agents can improve the agglomeration of sheet-like nano zinc oxide and the problem of poor organic-inorganic interface bonding. At the same time, the double bonds on the surface can participate in subsequent polymerization, thereby improving the gas barrier effect.

[0056] By comparing with Comparative Example 3, it can be found that crosslinking treatment can make the structure and pore defects smaller, thereby improving the gas barrier effect. In Comparative Example 4, no double bond crosslinking agent is used, and there is no additional free-moving double bond crosslinking agent to crosslink on the surface of pore defects. Relying solely on the crosslinkable structure of the material itself, the barrier effect achieved is poor. In Comparative Example 5, the impregnation was not sufficient, and the impregnation liquid did not completely penetrate into the pore defects, so the barrier effect achieved was poor.

[0057] Test Example 2: Antibacterial effect test Test Method: The antibacterial activity was tested using the inhibition zone method (GB / T 38483-2020). The plant-based modified packaging materials of each example and comparative example were pulverized and ground, then passed through a 200-mesh sieve. They were then mixed with pure water at a mass ratio of 1:19, ultrasonically dispersed, and 40 μL was immediately added to a 1 cm diameter filter paper disc. Under aseptic conditions, the sterilized nutrient agar medium was poured into a petri dish while still hot and allowed to cool and solidify naturally. 100 μL of bacterial suspension was transferred to the surface of the agar medium and spread evenly using a sterilized spreading rod. The loaded filter paper disc was then laid flat on the surface and incubated at 37°C for 24 hours. After incubation, the diameter of the inhibition zone was measured.

[0058] Durable antibacterial test: The plant-based modified packaging materials of each example and comparative example were placed in pure water and sonicated at room temperature for 24 hours. The diameter of the inhibition zone was then tested again. The results are shown in Table 2.

[0059] Table 2 A comparison of the experimental data in Table 2 shows that the plant-based modified packaging material prepared by this invention has good antibacterial effects.

[0060] Compared with Comparative Example 2, it can be found that without modification with double-bonded silane coupling agents, there are more defects, and it is easier to release zinc ions for sterilization.

[0061] By comparing with Comparative Example 6, it can be found that when only tung oil quaternary ammonium salt is used, the inhibition zone is smaller because tung oil quaternary ammonium salt participates in cross-linking and entanglement, which is a contact type of sterilization, and affects the surrounding charge balance. After 24 hours of pure water sonication, the inhibition zone is slightly expanded, which may be due to the hydrophilic nature of quaternary ammonium salt, causing the quaternary ammonium salt end to spread and concentrate outward during the soaking process.

[0062] A comparison with Comparative Example 7 reveals that tung oil quaternary ammonium salt has little effect on the range of the inhibition zone, with zinc ions playing a more dominant role in bactericidal activity.

[0063] Compared with Comparative Example 8, it can be found that when dodecyltrimethylammonium chloride is added alone, it is easy to migrate and be lost. It has a strong initial antibacterial effect, but it is not lasting.

[0064] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A plant-based modified packaging material, characterized in that, The plant-based modified packaging material is prepared by mixing double-bonded sheet-like nano zinc oxide, tung oil quaternary ammonium salt, polylactic acid and dichloromethane, drying them in a mold to form a plant-based modified film substrate, and then impregnating it with an impregnation solution.

2. The plant-based modified packaging material of claim 1, wherein, The double-bonded sheet-like zinc oxide nanoparticles are prepared by treating sheet-like zinc oxide nanoparticles with a double-bonded silane coupling agent.

3. The plant-based modified packaging material of claim 1, wherein, The tung oil quaternary ammonium salt is prepared by oxidizing tung oil with hydrogen peroxide, ring-opening with hydrochloric acid, and quaternizing with triethylamine.

4. The plant-based modified packaging material of claim 1, wherein, The impregnation solution is a mixture of a double bond crosslinking agent, a free radical initiator, and anhydrous ethanol.

5. A method for preparing a plant-based modified packaging material, characterized by, The preparation steps include the following: (1) Zinc nitrate hexahydrate, oleic acid, and deionized water are mixed evenly in a mass ratio of 1:(0.3~0.4):(60~70), and then urea with a molar amount of 30~40 times that of zinc nitrate hexahydrate is added. The mixture is placed in a sealed container and reacted at 130~140℃ for more than 12 hours. After cooling to room temperature, the mixture is centrifuged, washed and dried, and then calcined in a muffle furnace at 400~450℃ for more than 2 hours to obtain sheet-like nano zinc oxide. (2) Double-bonded sheet-like zinc oxide was prepared by treating sheet-like zinc oxide with a double-bonded silane coupling agent; (3) Mix tung oil and epoxidation catalyst at a mass ratio of 1:(0.03~0.04) evenly, then add hydrogen peroxide solution at a mass ratio of 0.6~0.7 times that of tung oil, stir and react at 40~45℃ for 30~40 min, wash, dry, and rotary evaporate to obtain epoxidized tung oil; Mix epoxidized tung oil and acetone at a mass ratio of 1:3 evenly, and under stirring conditions at 40~45℃, add 0.1mol / L hydrochloric acid solution of the same mass as epoxidized tung oil at a uniform rate within 2 h, wash with pure water and ethyl acetate until pH is neutral, take the upper organic phase, dry and rotary evaporate to obtain chlorinated tung oil; Mix chlorinated tung oil, triethylamine and tetrahydrofuran at a mass ratio of 1:(0.5~0.6):(40~50) evenly, react at 50℃ for more than 48 h, evaporate tetrahydrofuran and excess triethylamine to obtain tung oil quaternary ammonium salt; (4) Weigh 0.5%~5% of double-bonded sheet-like nano zinc oxide, 0.5%~9% of tung oil quaternary ammonium salt, and the remainder is polylactic acid. Mix the double-bonded sheet-like nano zinc oxide, tung oil quaternary ammonium salt, polylactic acid and dichloromethane in a mold and dry them to form a plant-based modified film substrate. (5) Mix the double bond crosslinking agent, free radical initiator and anhydrous ethanol to form an impregnation solution; immerse the plant-based modified film substrate in the impregnation solution, remove it and drain until no liquid drips, let it stand in an oven at 60~70℃ for 2~3 minutes, then put it in the impregnation solution for 5~10 seconds and remove it directly, drain until no liquid drips, let it stand in an oven at 160~170℃ for 3 minutes, wash it with pure water, and dry it to obtain the plant-based modified packaging material.

6. A method of making a plant-based modified packaging material according to claim 5, characterized in that, The double-bonded silane coupling agent in step (2) is one or a mixture of A-151, A-171, A-172 and KH570.

7. A method of making a plant-based modified packaging material according to claim 5, characterized in that, The epoxidation catalyst in step (3) is one or a mixture of molybdic acid, tungstic acid, phosphotungstic acid, molybdic acid peroxide complex, tungstic acid peroxide complex and phosphotungstic acid peroxide complex.

8. A method of making a plant-based modified packaging material according to claim 5, characterized in that, The double bond crosslinking agent in step (5) is one or a mixture of divinylbenzene, N,N'-methylenebisacrylamide, trimethylolpropane triacrylate, ethylene glycol diacrylate, 1,4-butanediol diacrylate and 1,6-hexanediol diacrylate.

9. A method of preparing a plant-based modified packaging material according to claim 5, characterized in that, The free radical initiator in step (5) is one or more of azobisisobutyronitrile, benzoyl peroxide, potassium persulfate, and ammonium persulfate.

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