Plant-based antibacterial packaging material and preparation method thereof

Abstract

The invention discloses a plant-based antibacterial packaging material and a preparation method thereof, and relates to the technical field of high polymer materials. When the plant-based antibacterial packaging material is prepared, catechinic aldehyde reacts with carboxymethyl chitosan, zinc ions are adsorbed, then 2-methylimidazole is added for in-situ growth of ZIF-8, vanillin is loaded, and antibacterial loaded carboxymethyl chitosan is prepared; the preparation method comprises the following steps: reacting tetramethyl-1, 6-hexamethylenediamine with 1-bromodecane to prepare a quaternary ammonium monomer; the preparation method comprises the following steps: reacting a quaternary ammonium monomer with 1, 6-dibromohexane to prepare a bromine-terminated quaternary ammonium monomer; modifying polyvinyl alcohol by using a bromine-terminated quaternary ammonium monomer to prepare quaternary ammonium modified polyvinyl alcohol; mixing the antibacterial loaded carboxymethyl chitosan, quaternary ammonium modified polyvinyl alcohol, corn straw fiber powder, glycerol and polylactic acid, and performing melt extrusion granulation to obtain the plant-based antibacterial packaging material. The prepared plant-based antibacterial packaging material has the advantages of being antibacterial, antioxidant, degradable, high in mechanical strength and good in barrier property.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, and in particular to a plant-based antibacterial packaging material and a preparation method thereof. Background Art

[0002] In food processing and preservation, pollution at the source, during processing, and during circulation are the main links that cause food safety risks. The first two points can be gradually curbed by strengthening government supervision and internal control of enterprises. However, how to resist the erosion of microorganisms during food circulation and preservation, especially high water activity foods that are conducive to the growth of microorganisms, such as fresh meat, fresh fruits and vegetables, sausage products, sauce packets, etc. How to preserve and resist bacteria while maintaining quality and extend the shelf life of such foods is a difficult point in food antibacterial.

[0003] At present, the most widely used methods for food preservation and antibacterial are pasteurization and the addition of preservatives and antimicrobial agents. However, pasteurization cannot completely kill all microorganisms in food, and the addition of preservatives will change the quality of food. At the same time, some preservatives have problems such as carcinogenicity, carcinogenicity, teratogenicity, and easy to cause food poisoning, which in turn creates hidden dangers for food safety. Other commonly used methods for antibacterial and food preservation include radiation sterilization, drying, freezing, refrigeration, vacuum and atmosphere preservation, and the addition of salt substances, but these methods also have certain limitations, either incomplete sterilization, or easy loss of antibacterial activity, or change of food quality, and are not applicable to some foods, especially foods with high water activity. In addition, since the growth of microorganisms starts from the surface of food, appropriate amounts of antibacterial substances are often sprayed or applied on the surface of food to improve its safety and inhibit the growth of microorganisms. However, since antibacterial substances easily interact with food components and lose their antibacterial activity, and the antibacterial activity is not persistent, they are not widely used.

[0004] Antimicrobial active packaging is a frontier and hot topic in the current research and development of food and materials. Antimicrobial active packaging is a packaging method that mixes antimicrobial agents into polymer packaging materials to make them have antimicrobial activity. Antimicrobial active packaging has antimicrobial activity and achieves the purpose of antimicrobial preservation inside the packaging, so as to gradually reduce or replace the preservatives added to the food. Antimicrobial active packaging replaces the traditional food preservation method of adding antimicrobial agents to food, can maintain the nutrition and flavor of food for a long time, extend the shelf life, improve safety, and can effectively solve the problem of antimicrobial preservation of high water activity food. Summary of the invention

[0005] The object of the present invention is to provide a plant-based antibacterial packaging material and a preparation method thereof, so as to solve the problems existing in the prior art.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A plant-based antibacterial packaging material, wherein the plant-based antibacterial packaging material is prepared by mixing antibacterial-loaded carboxymethyl chitosan, quaternary ammonium-modified polyvinyl alcohol, corn straw fiber powder, glycerol, and polylactic acid, and then melt-extruding and granulating the mixture;

[0008] The antibacterial loaded carboxymethyl chitosan is prepared by reacting catechin aldehyde with carboxymethyl chitosan, adsorbing zinc ions, then adding 2-methylimidazole to grow ZIF-8 in situ, and then loading vanillin.

[0009] The quaternary ammonium modified polyvinyl alcohol is prepared by modifying polyvinyl alcohol with a bromide-terminated quaternary ammonium monomer;

[0010] The bromide-terminated quaternary ammonium monomer is prepared by reacting a quaternary ammonium monomer with 1,6-dibromohexane;

[0011] The quaternary ammonium monomer is prepared by reacting N,N,N',N'-tetramethyl-1,6-hexanediamine with 1-bromodecane.

[0012] As an optimization, the degree of substitution of the carboxymethyl chitosan is greater than 80%, and the weight average molecular weight is 40-50 KDa.

[0013] As an optimization, the model of the polyvinyl alcohol is PVA2488.

[0014] As an optimization, the corn straw fiber powder is obtained by crushing corn straw with a high-speed crusher and sifting out powder with a particle size in the range of 20 to 40 meshes to obtain the corn straw fiber powder.

[0015] As an optimization, the model of the polylactic acid is 4032D, the melting point is 166°C, and the density is 1.25g / m 3 .

[0016] A method for preparing a plant-based antibacterial packaging material comprises the following steps:

[0017] (1) By weight, 2 to 3 parts of carboxymethyl chitosan were added to 30 parts of pure water, stirred at 300 to 400 r / min for 30 to 40 minutes at room temperature, 1 to 1.2 parts of catechin aldehyde were added, stirred at 300 to 400 r / min for 40 to 50 minutes at room temperature, 8 to 12 parts of 10 wt% zinc nitrate solution were added, stirred at 300 to 400 r / min for 60 to 80 minutes at room temperature, and 18.8 to 28.2 parts of 10 wt% zinc nitrate solution were added. % 2-methylimidazole solution, at room temperature, stir at 700-800r / min for 4-5h, add 5 parts of 2wt% vanillin solution, at room temperature, stir at 400-500r / min for 60-90min, add 80-85 parts of ethanol, stir at 200-300r / min for 30-40min, let stand for 4-5h, filter, wash the precipitate with ethanol 3-4 times, and vacuum dry at 40-50℃ for 8-10h to obtain antibacterial loaded carboxymethyl chitosan;

[0018] (2) Mix 20 to 24 parts of N,N,N',N'-tetramethyl-1,6-hexanediamine, 9 to 11 parts of 1-bromodecane, and 80 to 90 parts of acetone by mass, react at 50 to 60° C. and 300 to 400 r / min for 70 to 75 hours, remove the solvent by rotary evaporation, wash with n-hexane 3 to 4 times, take the lower layer of product, and prepare a quaternary ammonium monomer;

[0019] (3) Mix 5 to 6 parts of quaternary ammonium monomer, 40 to 45 parts of 1,6-dibromohexane and 40 to 45 parts of ethanol by weight, stir at 45 to 50° C. and 300 to 400 r / min for 40 to 42 hours, remove the solvent by rotary evaporation, wash with n-hexane 3 to 4 times, take the solid precipitate at the bottom, and vacuum dry it at 25 to 30° C. for 16 to 20 hours to obtain a brominated quaternary ammonium monomer;

[0020] (4) In a nitrogen atmosphere, 6 to 8 parts of polyvinyl alcohol, 0.3 to 0.4 parts of sodium carbonate, 1.5 to 2 parts of terminal bromide quaternary ammonium monomer, and 80 to 90 parts of N,N-dimethylformamide were mixed uniformly by weight, stirred at 80 to 90° C. and 400 to 500 r / min for 20 to 22 h, cooled naturally to room temperature, and precipitated with ethyl acetate, which was repeated three times, and the precipitate was vacuum dried at 60 to 70° C. for 10 to 12 h to obtain quaternary ammonium modified polyvinyl alcohol;

[0021] (5) Add 10 to 15 parts of antibacterial loaded carboxymethyl chitosan, 20 to 30 parts of quaternary ammonium modified polyvinyl alcohol, 20 to 30 parts of corn straw fiber powder, 3 to 5 parts of glycerol, and 30 to 40 parts of polylactic acid into a high-speed mixer, mix at 1200 to 1500 rpm for 10 to 15 min, seal and let stand for 20 to 24 h, add to a twin-screw extruder, melt extrude and granulate at 170 to 180 ° C and 110 to 120 rpm to obtain a plant-based antibacterial packaging material.

[0022] As an optimization, the reaction process of the quaternary ammonium monomer in step (2) is as follows:

[0023]

[0024] As an optimization, the reaction process of the bromide-terminated quaternary ammonium monomer in step (3) is as follows:

[0025]

[0026] As an optimization, the reaction process of the quaternary ammonium modified polyvinyl alcohol in step (4) is as follows:

[0027]

[0028] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0029] When preparing the plant-based antibacterial packaging material, the present invention first reacts catechin aldehyde with carboxymethyl chitosan, then adsorbs zinc ions, subsequently adds 2-methylimidazole to grow ZIF-8 in situ, and then loads vanillin to obtain antibacterial loaded carboxymethyl chitosan; reacts N,N,N',N'-tetramethyl-1,6-hexanediamine with 1-bromodecane to obtain a quaternary ammonium monomer; reacts the quaternary ammonium monomer with 1,6-dibromohexane to obtain a bromide-terminated quaternary ammonium monomer; modifies polyvinyl alcohol with the bromide-terminated quaternary ammonium monomer to obtain a quaternary ammonium-modified polyvinyl alcohol; and mixes the antibacterial loaded carboxymethyl chitosan, the quaternary ammonium-modified polyvinyl alcohol, corn straw fiber powder, glycerol, and polylactic acid, and then melt-extrudes and granulates them to obtain the plant-based antibacterial packaging material.

[0030] First, catechin aldehyde reacts with the amino group on carboxymethyl chitosan through the Schiff base reaction, and catechin aldehyde with a polyphenol structure is grafted on the carboxymethyl chitosan. The polyphenol structure on the carboxymethyl chitosan has good antioxidant properties and also provides sites for the complex loading of zinc ions. After the zinc ions are loaded, 2-methylimidazole is added to grow ZIF-8 in situ. ZIF-8 has good antibacterial properties and also provides a large number of loading sites, which provides sites for the subsequent loading of vanillin. At the same time, catechin aldehyde and vanillin both have aldehyde groups and can form Schiff base bonds with the amino groups on carboxymethyl chitosan. The Schiff base bond is a dynamic covalent bond, which will spontaneously break and recombine under weakly acidic conditions. At the same time, weak acidity is also the pH environment of bacterial body fluids, which can intelligently release antibacterial active factors for killing bacteria.

[0031] Secondly, the modification of polyvinyl alcohol with terminal quaternary ammonium monomer improves its antibacterial properties. The diquaternary ammonium structure contained therein has higher antibacterial activity, and can form a synergistic antibacterial effect with ZIF-8 and vanillin loaded with antibacterial carboxymethyl chitosan. At the same time, the positive charge carried by the diquaternary ammonium structure and the negative charge carried by the carboxyl group on the carboxymethyl chitosan can form an electrostatic bonding effect, which also improves the mechanical properties.

[0032] Finally, the antibacterial loaded carboxymethyl chitosan, quaternary ammonium modified polyvinyl alcohol, corn straw fiber powder, glycerol, and polylactic acid are mixed and melt extruded and granulated. After the obtained plant-based antibacterial packaging material is made into a film, in a high water vapor environment, the hydrophilic antibacterial loaded carboxymethyl chitosan, quaternary ammonium modified polyvinyl alcohol and hydrophobic polylactic acid will undergo microphase separation, and the hydrophilic phase in the inner layer will dissolve and migrate to the outer surface. In this process, the antibacterial active factors carried on it will also migrate out together to play an antibacterial role, which improves the utilization efficiency of the antibacterial active factors and allows the antibacterial performance to be maintained for a long time. In this process, the hydrophobic phase polylactic acid gradually moves to the middle section, providing a water vapor barrier effect to prevent external water vapor from entering the interior and causing erosion. At the same time, polyvinyl alcohol has excellent gas barrier properties. Under the blending of several materials, intermolecular forces such as intermolecular hydrogen bonding, electrostatic bonding, and coordination bonds also improve the gas barrier properties, while also improving the mechanical strength properties of the material. All materials are made of plant-based materials, natural macromolecules, and degradable materials. They will not cause excessive environmental pressure after use and are environmentally friendly materials. DETAILED DESCRIPTION

[0033] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0034] Embodiment 1:

[0035] A method for preparing a plant-based antibacterial packaging material, the method comprising the following steps:

[0036] (1) By weight, 2 parts of carboxymethyl chitosan were added to 30 parts of pure water, stirred at 300 r / min for 40 min at room temperature, 1 part of catechin was added, stirred at 300 r / min for 50 min at room temperature, 8 parts of 10 wt% zinc nitrate solution were added, stirred at 300 r / min for 80 min at room temperature, 18.8 parts of 10 wt% 2-methylimidazole solution were added, stirred at 700 r / min for 5 h at room temperature, 5 parts of 2 wt% vanillin solution were added, stirred at 400 r / min for 90 min at room temperature, 80 parts of ethanol were added, stirred at 200 r / min for 40 min, allowed to stand for 4 h, filtered, the precipitate was washed 3 times with ethanol, and vacuum dried at 40 ° C for 10 h to obtain antibacterial loaded carboxymethyl chitosan;

[0037] (2) By weight, 20 parts of N,N,N',N'-tetramethyl-1,6-hexanediamine, 9 parts of 1-bromodecane, and 80 parts of acetone were mixed uniformly, reacted at 50° C. and 300 r / min for 75 h, and the solvent was removed by rotary evaporation. The product was washed with n-hexane for 3 times, and the lower layer was taken to obtain a quaternary ammonium monomer;

[0038] (3) Mix 5 parts of quaternary ammonium monomer, 40 parts of 1,6-dibromohexane and 40 parts of ethanol by weight, stir at 45° C. and 300 r / min for 42 h, remove the solvent by rotary evaporation, wash with n-hexane 3 times, take the solid precipitate at the bottom, and vacuum dry at 25° C. for 20 h to obtain a brominated quaternary ammonium monomer;

[0039] (4) In nitrogen atmosphere, 6 parts of polyvinyl alcohol, 0.3 parts of sodium carbonate, 1.5 parts of bromine-terminated quaternary ammonium monomer, and 80 parts of N,N-dimethylformamide were mixed uniformly by weight, stirred at 80° C. and 400 r / min for 22 h, cooled naturally to room temperature, and precipitated with ethyl acetate. The mixture was repeated three times, and the precipitate was vacuum dried at 60° C. for 12 h to obtain quaternary ammonium-modified polyvinyl alcohol;

[0040] (5) By weight, 10 parts of antibacterial loaded carboxymethyl chitosan, 30 parts of quaternary ammonium modified polyvinyl alcohol, 20 parts of corn straw fiber powder, 3 parts of glycerol, and 40 parts of polylactic acid were added to a high-speed mixer, mixed at 1200 rpm for 15 min, sealed and allowed to stand for 20 h, added to a twin-screw extruder, and melt-extruded and granulated at 170°C and 110 rpm to obtain a plant-based antibacterial packaging material.

[0041] Embodiment 2:

[0042] A method for preparing a plant-based antibacterial packaging material, the method comprising the following steps:

[0043] (1) By weight, 2.5 parts of carboxymethyl chitosan were added to 30 parts of pure water, stirred at 350 r / min for 35 min at room temperature, 1.1 parts of catechin aldehyde were added, stirred at 350 r / min for 45 min at room temperature, 10 parts of 10 wt% zinc nitrate solution were added, stirred at 350 r / min for 70 min at room temperature, 23.5 parts of 10 wt% 2-methylimidazole solution were added, stirred at 750 r / min for 4.5 h at room temperature, 5 parts of 2 wt% vanillin solution were added, stirred at 450 r / min for 75 min at room temperature, 85 parts of ethanol were added, stirred at 250 r / min for 35 min, allowed to stand for 4.5 h, filtered, the precipitate was washed 4 times with ethanol, and vacuum dried at 45 ° C for 9 h to obtain antibacterial loaded carboxymethyl chitosan;

[0044] (2) By weight, 22 parts of N,N,N',N'-tetramethyl-1,6-hexanediamine, 10 parts of 1-bromodecane, and 85 parts of acetone were mixed uniformly, reacted at 55° C. and 350 r / min for 72 h, and the solvent was removed by rotary evaporation. The mixture was washed with n-hexane for 4 times, and the lower layer of the product was taken to obtain a quaternary ammonium monomer;

[0045] (3) 5.5 parts of quaternary ammonium monomer, 42 parts of 1,6-dibromohexane and 43 parts of ethanol were mixed uniformly by weight, stirred at 50° C. and 350 r / min for 41 h, and the solvent was removed by rotary evaporation. The mixture was washed with n-hexane for 4 times, and the solid precipitate at the bottom was taken and vacuum dried at 30° C. for 18 h to obtain a brominated quaternary ammonium monomer.

[0046] (4) In nitrogen atmosphere, 7 parts of polyvinyl alcohol, 0.35 parts of sodium carbonate, 1.8 parts of bromine-terminated quaternary ammonium monomer, and 85 parts of N,N-dimethylformamide were mixed uniformly, stirred at 85° C. and 450 r / min for 21 h, cooled naturally to room temperature, and precipitated with ethyl acetate. The mixture was repeated three times, and the precipitate was vacuum dried at 65° C. for 11 h to obtain quaternary ammonium-modified polyvinyl alcohol;

[0047] (5) By weight, 12 parts of antibacterial loaded carboxymethyl chitosan, 25 parts of quaternary ammonium modified polyvinyl alcohol, 25 parts of corn straw fiber powder, 4 parts of glycerol, and 35 parts of polylactic acid were added to a high-speed mixer, mixed at 1300 rpm for 12 min, sealed and allowed to stand for 22 h, added to a twin-screw extruder, and melt-extruded and granulated at 175°C and 115 rpm to obtain a plant-based antibacterial packaging material.

[0048] Embodiment 3:

[0049] A method for preparing a plant-based antibacterial packaging material, the method comprising the following steps:

[0050] (1) By weight, 3 parts of carboxymethyl chitosan were added to 30 parts of pure water, stirred at 400 r / min for 30 min at room temperature, 1.2 parts of catechin aldehyde were added, stirred at 400 r / min for 40 min at room temperature, 12 parts of 10 wt% zinc nitrate solution were added, stirred at 400 r / min for 60 min at room temperature, 28.2 parts of 10 wt% 2-methylimidazole solution were added, stirred at 800 r / min for 4 h at room temperature, 5 parts of 2 wt% vanillin solution were added, stirred at 500 r / min for 60 min at room temperature, 85 parts of ethanol were added, stirred at 300 r / min for 30 min, allowed to stand for 5 h, filtered, the precipitate was washed 4 times with ethanol, and vacuum dried at 50 ° C for 8 h to obtain antibacterial loaded carboxymethyl chitosan;

[0051] (2) By weight, 24 parts of N,N,N',N'-tetramethyl-1,6-hexanediamine, 11 parts of 1-bromodecane, and 90 parts of acetone were mixed uniformly, reacted at 60° C. and 400 r / min for 70 h, and the solvent was removed by rotary evaporation. The product was washed with n-hexane for 4 times, and the lower layer was taken to obtain a quaternary ammonium monomer;

[0052] (3) 6 parts of quaternary ammonium monomer, 45 parts of 1,6-dibromohexane and 45 parts of ethanol were mixed uniformly by weight, stirred at 50° C. and 400 r / min for 40 h, and the solvent was removed by rotary evaporation. The mixture was washed with n-hexane for 4 times, and the solid precipitate at the bottom was taken and vacuum dried at 30° C. for 16 h to obtain a brominated quaternary ammonium monomer.

[0053] (4) In a nitrogen atmosphere, 8 parts of polyvinyl alcohol, 0.4 parts of sodium carbonate, 2 parts of bromine-terminated quaternary ammonium monomer, and 90 parts of N,N-dimethylformamide were mixed uniformly by weight, stirred at 90° C. and 500 r / min for 20 h, cooled naturally to room temperature, and precipitated with ethyl acetate. The mixture was repeated three times, and the precipitate was vacuum dried at 70° C. for 10 h to obtain quaternary ammonium-modified polyvinyl alcohol;

[0054] (5) By weight, 15 parts of antibacterial loaded carboxymethyl chitosan, 20 parts of quaternary ammonium modified polyvinyl alcohol, 30 parts of corn straw fiber powder, 5 parts of glycerol, and 30 parts of polylactic acid were added to a high-speed mixer, mixed at 1500 rpm for 10 min, sealed and allowed to stand for 24 h, added to a twin-screw extruder, and melt-extruded and granulated at 180°C and 120 rpm to obtain a plant-based antibacterial packaging material.

[0055] Comparative Example 1:

[0056] The preparation method of the plant-based antibacterial packaging material of Comparative Example 1 is different from that of Example 2 in that steps (2), (3) and (4) are not performed, and step (5) is modified as follows: by weight, 12 parts of antibacterial-loaded carboxymethyl chitosan, 25 parts of polyvinyl alcohol, 25 parts of corn straw fiber powder, 4 parts of glycerol, and 35 parts of polylactic acid are added to a high-speed mixer, mixed at 1300 rpm for 12 min, sealed and allowed to stand for 22 h, added to a twin-screw extruder, melt-extruded and granulated at 175° C. and 115 rpm to obtain a plant-based antibacterial packaging material. The remaining steps are the same as those of Example 2.

[0057] Comparative Example 2:

[0058] The preparation method of the plant-based antibacterial packaging material of Comparative Example 2 is different from that of Example 2 in that steps (2), (3) and (4) are not performed, and step (5) is modified as follows: by weight, 25 parts of antibacterial-loaded carboxymethyl chitosan, 25 parts of corn straw fiber powder, 4 parts of glycerol, and 35 parts of polylactic acid are added to a high-speed mixer, mixed at 1300 rpm for 12 min, sealed and allowed to stand for 22 h, added to a twin-screw extruder, melt-extruded and granulated at 175° C. and 115 rpm to obtain a plant-based antibacterial packaging material. The remaining steps are the same as those of Example 2.

[0059] Comparative Example 3:

[0060] The difference between the preparation method of the plant-based antibacterial packaging material of Comparative Example 3 and Example 2 is that step (1) is different, and step (1) is modified as follows: by mass, 2.5 parts of carboxymethyl chitosan are added to 30 parts of pure water, stirred at room temperature, 350r / min for 35min, 1.1 parts of catechin aldehyde are added, stirred at room temperature, 350r / min for 45min, 10 parts of 10wt% zinc nitrate solution are added, stirred at room temperature, 350r / min for 70min, 23.5 parts of 10wt% 2-methylimidazole solution are added, stirred at room temperature, 750r / min for 4.5h, 85 parts of ethanol are added, stirred at 250r / min for 35min, let stand for 4.5h, filter, wash the precipitate with ethanol 4 times, and vacuum dry at 45°C for 9h to obtain antibacterial loaded carboxymethyl chitosan. The remaining steps are the same as Example 2.

[0061] Comparative Example 4:

[0062] The preparation method of the plant-based antibacterial packaging material of Comparative Example 4 is different from that of Example 2 in that step (1) is different, and step (1) is modified as follows: by mass, 2.5 parts of carboxymethyl chitosan are added to 30 parts of pure water, stirred at room temperature at 350 r / min for 35 min, 1.1 parts of catechins are added, stirred at room temperature at 350 r / min for 45 min, 5 parts of 2wt% vanillin solution are added, stirred at room temperature at 450 r / min for 75 min, 85 parts of ethanol are added, stirred at 250 r / min for 35 min, allowed to stand for 4.5 h, filtered, the precipitate is washed with ethanol 4 times, and vacuum dried at 45°C for 9 h to obtain antibacterial loaded carboxymethyl chitosan. The remaining steps are the same as those of Example 2.

[0063] Comparative Example 5:

[0064] The difference between the preparation method of the plant-based antibacterial packaging material of Comparative Example 5 and Example 2 is that step (1) is different, and step (1) is modified as follows: by mass, 2.5 parts of carboxymethyl chitosan are added to 30 parts of pure water, stirred at room temperature, 350r / min for 35min, 5 parts of 2wt% vanillin solution are added, stirred at room temperature, 450r / min for 75min, 10 parts of 10wt% zinc nitrate solution are added, stirred at room temperature, 350r / min for 70min, 23.5 parts of 10wt% 2-methylimidazole solution are added, stirred at room temperature, 750r / min for 4.5h, 85 parts of ethanol are added, stirred at 250r / min for 35min, let stand for 4.5h, filter, wash the precipitate with ethanol 4 times, and vacuum dry at 45°C for 9h to obtain antibacterial loaded carboxymethyl chitosan. The remaining steps are the same as those in Example 2.

[0065] The plant-based antibacterial packaging material prepared above was melt-extruded at 180° C. to form a film with a thickness of 0.05 mm to obtain a plant-based antibacterial film for testing.

[0066] Test Example 1:

[0067] Mechanical properties test: refer to GB / T 1040.3-2006 to test tensile strength and elongation at break, use type 5 specimens, the tensile rate is 5mm / min, test 5 samples in each group, and take the average value for record.

[0068] The results are shown in Table 1.

[0069] Table 1

[0070] Tensile strength / MPa Elongation at break Example 1 56.31 148.27％ Example 2 58.28 152.61％ Example 3 56.87 147.59％ Comparative Example 1 41.24 121.38％ Comparative Example 2 35.47 61.41％ Comparative Example 3 52.15 142.33％ Comparative Example 4 49.36 137.13％ Comparative Example 5 48.15 134.39％

[0071] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 5 in Table 1, it can be found that the plant-based antibacterial packaging material prepared by the present invention has good tensile strength and elongation at break.

[0072] By comparing the data in the table, it is shown that the quaternary ammonium modification of polyvinyl alcohol improves the tensile strength and elongation at break. The quaternary ammonium groups on it form an electrostatic bond with the carboxyl groups on carboxymethyl chitosan, thereby improving the mechanical strength. At the same time, polyvinyl alcohol also greatly improves the elongation at break.

[0073] Test Example 2:

[0074] Antibacterial performance test: refer to GB / T 31402-2023 to test the antibacterial performance, use the plate count method, the bacteria used are Staphylococcus aureus and Escherichia coli, calculate the inhibition rate and record it, test 5 samples in each group, and take the average value for recording.

[0075] The results are shown in Table 2.

[0076] Table 2

[0077]

[0078]

[0079] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 5 in Table 2, it can be found that the plant-based antibacterial packaging material prepared by the present invention has good antibacterial properties.

[0080] By comparing the data in the table, it is shown that the diquaternary ammonium structure on the quaternary ammonium modified polyvinyl alcohol provides a large amount of antibacterial activity. At the same time, the introduction of vanillin, ZIF-8 and catechin aldehyde effectively improves the antibacterial activity and produces a synergistic antibacterial effect.

[0081] Test Example 3:

[0082] Barrier performance test: refer to GB / T 19789-2021 to test the oxygen permeability coefficient to evaluate its oxygen barrier properties, the test conditions are 25℃ and relative humidity is 50%; refer to GB / T 30412-2013 to test the water vapor permeability to test its water vapor barrier properties, the test conditions are 25℃ and the relative humidity difference is 75%, 5 samples are tested in each group, and the average value is recorded.

[0083] The results are shown in Table 3.

[0084] Table 3

[0085] <![CDATA[Oxygen permeability coefficient cm 3 / (m 2 ·24h·0.1Mpa)]]> <![CDATA[Water vapor transmission rate g / (m 2 ·24h)]]> Example 1 0.54 85.44 Example 2 0.49 83.15 Example 3 0.51 86.78 Comparative Example 1 0.56 91.54 Comparative Example 2 4.15 78.12 Comparative Example 3 0.55 84.16 Comparative Example 4 0.52 86.24 Comparative Example 5 0.53 83.95

[0086] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 5 in Table 3, it can be found that the plant-based antibacterial packaging material prepared in the present invention has good barrier properties.

[0087] Comparison of the data in the table shows that the addition of polyvinyl alcohol effectively improves the oxygen permeability coefficient and slightly increases the water vapor permeability.

[0088] Test Example 4:

[0089] Antioxidant performance test: DPPH method and ABTS method were used to test its antioxidant capacity. The specific test methods are as follows:

[0090] DPPH method: add 5 mg of plant-based antibacterial packaging material to 1.5 mL of DPPH solution, mix and place in a dark room temperature environment for 40 minutes, measure its absorbance at a wavelength of 517 nm, use the blank solution as a control, calculate its DPPH free radical scavenging rate, test 3 samples in each group, and record the average value;

[0091] ABTS method: Add 5 mg of plant-based antibacterial packaging material to 1.5 mL of ABTS solution, mix and let stand in a dark room temperature environment for 6 hours, measure its absorbance at a wavelength of 734 nm, and use the blank solution as a control to calculate its ABTS free radical scavenging rate. Test 3 samples in each group and record the average value.

[0092] The results are shown in Table 4.

[0093] Table 4

[0094] DPPH free radical scavenging rate ABTS free radical scavenging rate Example 1 81.47％ 93.52％ Example 2 82.54％ 94.32％ Example 3 81.85％ 94.17％ Comparative Example 1 80.12％ 92.68％ Comparative Example 2 79.34％ 91.96％ Comparative Example 3 43.19％ 48.44％ Comparative Example 4 53.58％ 57.71％ Comparative Example 5 29.28％ 36.83％

[0095] From the comparison of the experimental data of Examples 1 to 3 and Comparative Examples 1 to 5 in Table 4, it can be found that the plant-based antibacterial packaging material prepared by the present invention has good antioxidant properties.

[0096] By comparing the data in the table, it can be seen that the introduction of vanillin and catechin aldehyde greatly improved the antioxidant capacity of the material and effectively scavenged free radicals. The in situ growth of ZIF-8 also brought a large number of loading sites, allowing more vanillin to be loaded. Vanillin and catechin aldehyde also produced a synergistic effect.

[0097] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method 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 in the scope of protection of the present invention.

Claims

1. A plant-based antibacterial packaging material, characterized in that: The plant-based antibacterial packaging material is prepared by mixing antibacterial-loaded carboxymethyl chitosan, quaternary ammonium-modified polyvinyl alcohol, corn stalk fiber powder, glycerol, and polylactic acid, and then melt-extruding and granulating the mixture. The antibacterial loaded carboxymethyl chitosan is prepared by reacting catechin aldehyde with carboxymethyl chitosan, adsorbing zinc ions, then adding 2-methylimidazole to grow ZIF-8 in situ, and then loading vanillin. The quaternary ammonium modified polyvinyl alcohol is prepared by modifying polyvinyl alcohol with a bromide-terminated quaternary ammonium monomer; The bromide-terminated quaternary ammonium monomer is prepared by reacting a quaternary ammonium monomer with 1,6-dibromohexane; The quaternary ammonium monomer is prepared by reacting N,N,N',N'-tetramethyl-1,6-hexanediamine with 1-bromodecane.

2. The plant-based antibacterial packaging material according to claim 1, characterized in that: The substitution degree of the carboxymethyl chitosan is greater than 80%, and the weight average molecular weight is 40-50 KDa.

3. The plant-based antibacterial packaging material according to claim 1, characterized in that: The model of the polyvinyl alcohol is PVA2488.

4. The plant-based antibacterial packaging material according to claim 1, characterized in that: The corn stalk fiber powder is obtained by crushing corn stalks with a high-speed crusher and sieving out powder with a particle size in the range of 20 to 40 meshes.

5. The plant-based antibacterial packaging material according to claim 1, characterized in that: The polylactic acid model is 4032D, the melting point is 166°C, and the density is 1.25 g / m 3 .

6. A method for preparing a plant-based antibacterial packaging material, characterized in that: The method comprises the following preparation steps: (1) By weight, 2 to 3 parts of carboxymethyl chitosan were added to 30 parts of pure water, stirred at 300 to 400 r / min for 30 to 40 minutes at room temperature, 1 to 1.2 parts of catechin aldehyde were added, stirred at 300 to 400 r / min for 40 to 50 minutes at room temperature, 8 to 12 parts of 10 wt% zinc nitrate solution were added, stirred at 300 to 400 r / min for 60 to 80 minutes at room temperature, and 18.8 to 28.2 parts of 10 wt% zinc nitrate solution were added. % 2-methylimidazole solution, at room temperature, stir at 700-800r / min for 4-5h, add 5 parts of 2wt% vanillin solution, at room temperature, stir at 400-500r / min for 60-90min, add 80-85 parts of ethanol, stir at 200-300r / min for 30-40min, let stand for 4-5h, filter, wash the precipitate with ethanol 3-4 times, and vacuum dry at 40-50℃ for 8-10h to obtain antibacterial loaded carboxymethyl chitosan; (2) Mix 20 to 24 parts of N,N,N',N'-tetramethyl-1,6-hexanediamine, 9 to 11 parts of 1-bromodecane, and 80 to 90 parts of acetone by mass, react at 50 to 60° C. and 300 to 400 r / min for 70 to 75 hours, remove the solvent by rotary evaporation, wash with n-hexane 3 to 4 times, take the lower layer of product, and prepare a quaternary ammonium monomer; (3) Mix 5 to 6 parts of quaternary ammonium monomer, 40 to 45 parts of 1,6-dibromohexane and 40 to 45 parts of ethanol by weight, stir at 45 to 50° C. and 300 to 400 r / min for 40 to 42 hours, remove the solvent by rotary evaporation, wash with n-hexane 3 to 4 times, take the solid precipitate at the bottom, and vacuum dry it at 25 to 30° C. for 16 to 20 hours to obtain a brominated quaternary ammonium monomer; (4) In a nitrogen atmosphere, 6 to 8 parts of polyvinyl alcohol, 0.3 to 0.4 parts of sodium carbonate, 1.5 to 2 parts of terminal bromide quaternary ammonium monomer, and 80 to 90 parts of N,N-dimethylformamide were mixed uniformly by weight, stirred at 80 to 90° C. and 400 to 500 r / min for 20 to 22 h, cooled naturally to room temperature, and precipitated with ethyl acetate, which was repeated three times, and the precipitate was vacuum dried at 60 to 70° C. for 10 to 12 h to obtain quaternary ammonium modified polyvinyl alcohol; (5) Add 10 to 15 parts of antibacterial loaded carboxymethyl chitosan, 20 to 30 parts of quaternary ammonium modified polyvinyl alcohol, 20 to 30 parts of corn straw fiber powder, 3 to 5 parts of glycerol, and 30 to 40 parts of polylactic acid into a high-speed mixer, mix at 1200 to 1500 rpm for 10 to 15 min, seal and let stand for 20 to 24 h, add to a twin-screw extruder, melt extrude and granulate at 170 to 180 ° C and 110 to 120 rpm to obtain a plant-based antibacterial packaging material.

7. The method for preparing a plant-based antibacterial packaging material according to claim 6, characterized in that: The reaction process of the quaternary ammonium monomer in step (2) is as follows:

8. The method for preparing a plant-based antibacterial packaging material according to claim 6, characterized in that: The reaction process of the bromide-terminated quaternary ammonium monomer in step (3) is as follows:

9. The method for preparing a plant-based antibacterial packaging material according to claim 6, characterized in that: The reaction process of the quaternary ammonium modified polyvinyl alcohol in step (4) is as follows:

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