A controlled-release antibacterial packaging film material and its preparation method

Abstract

This invention discloses a controlled-release antibacterial packaging film material and its preparation method, belonging to the technical field of packaging film materials. It addresses the technical problems of poor hydrophobicity, poor mechanical properties, and difficulty in maintaining antibacterial efficacy in existing starch-based food packaging films. The invention includes the following steps: mixing and stirring a crosslinking agent, distilled water, starch, composite lignin, and a plasticizer to obtain a film-forming suspension; adding antibacterial microspheres to the film-forming suspension; reacting at 70-80℃ for 30-60 minutes to obtain a film-forming liquid; and casting the film-forming liquid to form a film, thus obtaining a controlled-release antibacterial packaging film material. In this invention, lignin undergoes a Mannich reaction to introduce urea functional groups. The urea-modified lignin reacts with a coupling agent (3-isocyanopropyl)triethoxysilane, and is then composited with reinforcing materials to improve its mechanical properties and hydrophobicity. The antibacterial monomer is prepared into microspheres, giving it controlled-release and long-term antibacterial efficacy.

Description

Technical Field

[0001] This invention relates to the field of plastic packaging film technology, specifically to a controlled-release antibacterial packaging film material and its preparation method. Background Technology

[0002] Every year, a large amount of food spoils due to microbial activity, resulting in serious waste of food resources. In addition, many foodborne spoilage bacteria multiply in food and produce toxins, which enter the human body along with the food, causing foodborne diseases and affecting people's health.

[0003] Antibacterial food packaging materials can effectively protect food from bacterial contamination for a long time, playing an important role in food safety and human health. Therefore, enhancing the antibacterial properties of food packaging film materials is of positive significance. However, simply adding natural antibacterial agents to food packaging film materials is difficult to maintain their antibacterial efficacy and cannot achieve a long-lasting sterilization effect.

[0004] Petroleum-based packaging materials are widely used in food packaging due to their low cost and good mechanical properties. However, plastic packaging has disadvantages such as resource scarcity, non-renewability, and extreme difficulty in biodegradation, which cause serious harm to human health and the ecological environment. Therefore, research on the development of biodegradable and environmentally friendly antibacterial food packaging materials has received widespread attention. However, natural polymer materials, represented by starch, have natural hydrophilicity. After the starch polymer network absorbs water, it will destroy the structural integrity of the matrix and lead to poor barrier properties. In addition, starch-based food packaging films have poor mechanical properties. How to prepare green and environmentally friendly food packaging film materials with long-lasting antibacterial effects and excellent mechanical properties is an urgent technical problem to be solved.

[0005] Patent application CN113234307A discloses a fully degradable antibacterial food packaging film and its preparation method. The food packaging film contains starch, bio-based degradable polyester, organically modified montmorillonite, and natural antibacterial agents. By adding natural antibacterial agents, the antibacterial properties of the food packaging film are improved. Organic montmorillonite is used to improve its mechanical and barrier properties, and biodegradable polyester is used to improve its degradability. However, natural antibacterial agents have the disadvantage of not being able to maintain their own antibacterial properties, and the mechanical properties of montmorillonite itself are relatively poor compared to other inorganic materials.

[0006] To address the aforementioned technical shortcomings, a solution is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a controlled-release antibacterial packaging film material and its preparation method, which solves the technical problems of poor hydrophobicity, poor mechanical properties, and difficulty in maintaining antibacterial efficacy in food packaging films made from natural polymer materials such as starch in the prior art.

[0008] The objective of this invention can be achieved through the following technical solution: a method for preparing a controlled-release antibacterial packaging film material, comprising the following steps:

[0009] S1, crosslinking agent, distilled water, starch, composite lignin and plasticizer are mixed and stirred to obtain a film-forming suspension;

[0010] S2. Add antibacterial microspheres to the film-forming suspension and react at 70-80℃ for 30-60 min to obtain the film-forming solution;

[0011] S3. The film-forming solution was degassed under a vacuum of 0.09 MPa for 30 min, and then discharged at 0.15-2 g / cm³. 2 The areal density was cast into a petri dish, dried at 45-60℃ for 6 hours, cooled and peeled off to obtain a controlled-release antibacterial packaging film material.

[0012] This invention uses composite lignin and starch as the main film-forming materials, adds crosslinking agents and plasticizers as functional additives, and adds antibacterial microspheres with controlled-release antibacterial effects to prepare packaging film materials using a solution casting method.

[0013] Furthermore, the modified lignin is prepared by the following steps:

[0014] A1. Mix urea-modified lignin, (3-isocyanopropyl)triethoxysilane and DMF, and react at room temperature for 2-3 hours to obtain modified lignin;

[0015] The imino group in urea-modified lignin reacts with the isocyanate group of (3-isocyanopropyl)triethoxysilane to generate aminourea, thereby preparing (3-isocyanopropyl)triethoxysilane-modified lignin.

[0016] Taking coumarol, a monomer in lignin, as an example, the reaction formula for urea-modified lignin and (3-isocyanopropyl)triethoxysilane is as follows:

[0017]

[0018] A2. Mix fly ash microspheres, wollastonite and dolomite evenly to obtain an inorganic mixture; grind the inorganic mixture to obtain a reinforcing material with an average particle size of 30-40μm;

[0019] A3. Stir the reinforcing material and anhydrous ethanol at high speed to obtain a mixture; mix the mixture with the modified lignin and react at 80-90℃ for 100-120 min. After the reaction is completed, filter while hot to obtain a filter cake; wash the filter cake three times with anhydrous ethanol, then dry and pulverize to obtain composite lignin.

[0020] Fly ash microspheres, wollastonite, and dolomite, as inorganic materials, have a certain amount of hydroxyl groups on their surfaces, which can undergo hydrolysis reactions with siloxanes on the surface of modified lignin to obtain composite lignin. In addition, the surface area of ​​the reinforcing material ground to the micron level is significantly increased, which can lead to physical adsorption with modified lignin.

[0021] Further, in step A1, the urea-modified lignin is prepared by the following steps:

[0022] Formaldehyde was placed in an ice bath at -20°C, followed by the addition of lignin and urea, and the mixture was stirred to obtain a premixed solution. 0.1 mol / L HCl solution was added dropwise to the premixed solution to adjust its pH to 3-4. The premixed solution was reacted at 50-60°C for 2-3 hours, then filtered to obtain a solid. The solid was washed with deionized water and vacuum dried to constant weight to obtain urea-modified lignin.

[0023] Taking coumarol, a monomer of lignin, as an example, the reaction formula for the Mannich reaction of coumarol, formaldehyde, and urea to generate urea-modified lignin is as follows:

[0024]

[0025] Furthermore, the ratio of formaldehyde, lignin, and urea used is 30mL:20-30g:5-10g, and the vacuum drying temperature is 60-70℃.

[0026] Further, in step A1, the ratio of urea-modified lignin, (3-isocyanopropyl)triethoxysilane, and DMF is 20-30g:10-20g:200mL; in step A2, the ratio of fly ash microspheres, wollastonite, and dolomite is 10-20g:10g:10g; the grinding medium is zirconia balls, the grinding speed is 200-400r / min, and the grinding time is 30-60min; in step A3, the ratio of reinforcing material to anhydrous ethanol is 20g:50mL, and the amount of modified lignin is 80-100g.

[0027] Furthermore, the method for preparing antibacterial microspheres includes the following steps:

[0028] B1. Sodium dodecyl sulfonate and deionized water are mixed and stirred until completely dissolved to obtain an emulsifier solution; the emulsifier solution, chlorhexidine, and chlorhexidine gluconate are mixed and stirred to obtain intermediate A;

[0029] B2. Intermediate A, styrene and N,N-methylenebisacrylamide are mixed and stirred to obtain a premix; then an emulsifier solution is added dropwise to the premix. After the addition is complete, the mixture is stirred at 80-85℃ for 2-3 hours to obtain an emulsion.

[0030] B3. Dialyze the emulsion, with the dialysis bag retaining a relative molecular weight of 8000-14000 kDa. After separation for 3 days, freeze-dry for 10-12 hours to obtain a white powder, which is the antibacterial agent microsphere.

[0031] Antibacterial agent microspheres were prepared by emulsion polymerization using chlorhexidine and chlorhexidine gluconate as hydrophilic antibacterial monomers, styrene as a hydrophobic comonomer, N,N-methylenebisacrylamide as a crosslinking monomer, water as a reaction medium, and potassium persulfate as an initiator.

[0032] Further, in step B1, the ratio of sodium dodecyl sulfonate to deionized water is 10g:100mL, and the ratio of chlorhexidine to chlorhexidine gluconate is 5-10g:5-10g; in step B2, the ratio of styrene to N,N-methylenebisacrylamide is 20-30g:10-20g.

[0033] Further, in step S1, the crosslinking agent is sodium alginate, and the plasticizer is glycerol; the ratio of crosslinking agent, distilled water, starch, composite lignin and plasticizer is 1.5-2g:200mL:30-40g:5-10g:5g, the mixing speed is 100r / min, and the mixing time is 10min; in step S2, the amount of antibacterial microspheres is 5-10g.

[0034] In another aspect, the present invention can also prepare a controlled-release antibacterial packaging film material using a method for preparing a controlled-release antibacterial packaging film material.

[0035] The present invention has the following beneficial effects:

[0036] 1. The packaging film material prepared by this invention uses starch and composite lignin as the main film-forming materials, with the addition of a certain amount of additives and antibacterial microspheres with controlled-release antibacterial effects, and is then prepared by casting method. The controlled-release antibacterial packaging film material prepared by this invention has excellent mechanical properties and good antibacterial properties. Lignin is first subjected to the Mannich reaction to obtain urea-modified lignin; urea-modified lignin reacts with coupling agent (3-isocyanopropyl)triethoxysilane to introduce silicon-oxygen bonds on the lignin surface, thereby improving the high temperature resistance, chemical stability and hydrophobicity of lignin itself; silicon-oxygen bonds enrich the types and number of lignin's own skeleton; when starch and lignin are combined, the hydrophilicity of starch can be effectively improved, and the waterproof performance of the prepared packaging film material can be improved; in addition, when starch and lignin are combined as the main film-forming materials, they can form a rich polymer network structure, improving their mechanical properties.

[0037] 2. This invention combines modified lignin with reinforcing materials to prepare composite lignin. The reinforcing materials include fly ash microspheres, wollastonite, and dolomite. The hydroxyl groups on the surface of the inorganic materials react with the coupling agent on the surface of the modified lignin, thereby obtaining inorganic-reinforced composite lignin. Fly ash is a solid waste emitted by thermal power plants. Although hollow microspheres extracted from fly ash after power plant combustion have a slightly wider particle size distribution and lower purity, they can be used as reinforcing materials for modified lignin. Wollastonite, as a silicate mineral, has high hardness. Adding dolomite as an inorganic material to modified lignin provides properties similar to those of adding light calcium carbonate, significantly increasing the reinforcing properties of the modified lignin. Furthermore, grinding the above inorganic mixture to the micron level results in a significantly larger specific surface area for the inorganic materials, enabling the formation of larger interfacial phases and boundary regions with polymer materials, thereby improving the mechanical properties and water barrier properties of the prepared packaging film material.

[0038] 3. This invention uses chlorhexidine and chlorhexidine gluconate as antibacterial monomers. Chlorhexidine has the strongest bactericidal effect against Gram-positive bacteria, while chlorhexidine gluconate has lysozyme activity and strong bactericidal effects against Escherichia coli, Staphylococcus aureus, and Candida albicans. Organic small molecule antibacterial agents can effectively disrupt the integrity of cell membranes and effectively resist bacterial, mold, and fungal infections. In addition, the above-mentioned antibacterial monomers, as natural antibacterial agents, have the advantages of good biocompatibility and no pollution during production and use. Using styrene as a comonomer and N,N-methylenebisacrylamide as a crosslinking monomer, the above-mentioned antibacterial monomers are prepared into antibacterial agent microspheres with controlled-release effect. The antibacterial agent microspheres are then added to a film-forming suspension to prepare a controlled-release antibacterial packaging film material. Compared with volatile small molecule organic antibacterial agents, antibacterial agent microspheres have the characteristics of long-lasting antibacterial effect, which can meet the requirements of long-lasting and sustained-release antibacterial efficacy. Detailed Implementation

[0039] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Example 1

[0041] This embodiment provides a method for preparing composite lignin, including the following steps:

[0042] A1. Add 30 mL of formaldehyde to a 200 mL three-necked reaction flask and place the flask in an ice bath at -20 °C. Then add 20 g of lignin and 5 g of urea to the flask and mix and stir at 100 r / min for 10 min to obtain a premix. Add 0.1 mol / L HCl solution dropwise to the premix to adjust the pH to 3. Connect one end of the three-necked reaction flask to a reflux condenser and the other end to a magnetic stirrer, and then seal the three-necked reaction flask. Transfer the three-necked reaction flask to a water bath and set the water bath temperature to 50 °C. React at 100 r / min for 2 h, then filter to obtain a solid. Wash the solid three times with deionized water and vacuum dry at 60 °C to constant weight to obtain urea-modified lignin.

[0043] A2. Add 20g of urea-modified lignin, 10g of (3-isocyanopropyl)triethoxysilane and 200mL of DMF to a beaker, and react at room temperature with mechanical stirring at 100r / min for 2h to obtain modified lignin.

[0044] A3. Mix 10g of fly ash microspheres, 10g of wollastonite and 10g of dolomite evenly to obtain an inorganic mixture; transfer the inorganic mixture to a grinder, use zirconia balls as the grinding medium, grind at a speed of 200r / min for 30min, and grind to obtain a reinforcing material with an average particle size of 30μm.

[0045] A4. Add 20g of reinforcing material to 50mL of anhydrous ethanol and disperse in a high-speed disperser at 1000r / min for 10min to obtain a mixture. Transfer the mixture to a 500mL three-necked flask, add 80g of modified lignin, connect one end of the three-necked flask to a reflux condenser, and then transfer the three-necked flask to a water bath. React at 80℃ for 100min with stirring at 300r / min. After the reaction is complete, filter while hot to obtain a filter cake. Wash the filter cake three times with anhydrous ethanol, then dry and pulverize to obtain composite lignin.

[0046] Example 2

[0047] This embodiment provides a method for preparing composite lignin, including the following steps:

[0048] A1. Add 30 mL of formaldehyde to a 500 mL three-necked reaction flask and place the flask in an ice bath at -20 °C. Then add 25 g of lignin and 6 g of urea to the flask and mix and stir at 100 r / min for 15 min to obtain a premix. Add 0.1 mol / L HCl solution dropwise to the premix to adjust the pH to 3.3. Connect one end of the three-necked reaction flask to a reflux condenser and the other end to a magnetic stirrer, then seal the three-necked reaction flask. Transfer the three-necked reaction flask to a water bath and set the water bath temperature to 56 °C. React at 150 r / min for 2.5 h, then filter to obtain a solid. Wash the solid three times with deionized water and vacuum dry at 66 °C to constant weight to obtain urea-modified lignin.

[0049] A2. Add 25g of urea-modified lignin, 15g of (3-isocyanopropyl)triethoxysilane and 200mL of DMF to a beaker, and react at room temperature with mechanical stirring at 150r / min for 2.3h to obtain modified lignin.

[0050] A3. Mix 15g of fly ash microspheres, 10g of wollastonite and 10g of dolomite evenly to obtain an inorganic mixture; transfer the inorganic mixture to a grinder, use zirconia balls as the grinding medium, grind at a speed of 300r / min for 40min, and grind to obtain a reinforcing material with an average particle size of 35μm.

[0051] A4. Add 20g of reinforcing material to 50mL of anhydrous ethanol and disperse in a high-speed disperser at 1500r / min for 10min to obtain a mixture. Transfer the mixture to a 500mL three-necked flask, add 90g of modified lignin, connect one end of the three-necked flask to a reflux condenser, and then transfer the three-necked flask to a water bath. React at 85℃ for 110min with stirring at 400r / min. After the reaction is complete, filter while hot to obtain a filter cake. Wash the filter cake three times with anhydrous ethanol, then dry and pulverize to obtain composite lignin.

[0052] Example 3

[0053] This embodiment provides a method for preparing composite lignin, including the following steps:

[0054] A1. Add 30 mL of formaldehyde to a 500 mL three-necked reaction flask and place the flask in an ice bath at -20 °C. Then add 30 g of lignin and 10 g of urea to the flask and mix and stir at 100 r / min for 20 min to obtain a premix. Add 0.1 mol / L HCl solution dropwise to the premix to adjust the pH to 4. Connect one end of the three-necked reaction flask to a reflux condenser and the other end to a magnetic stirrer, and then seal the three-necked reaction flask. Transfer the three-necked reaction flask to a water bath and set the water bath temperature to 60 °C. React at 200 r / min for 3 h, then filter to obtain a solid. Wash the solid three times with deionized water and vacuum dry at 70 °C to constant weight to obtain urea-modified lignin.

[0055] A2. Add 30g of urea-modified lignin, 20g of (3-isocyanopropyl)triethoxysilane and 200mL of DMF to a beaker, and react at room temperature with mechanical stirring at 200r / min for 3h to obtain modified lignin.

[0056] A3. Mix 20g of fly ash microspheres, 10g of wollastonite and 10g of dolomite evenly to obtain an inorganic mixture; transfer the inorganic mixture to a grinder, use zirconia balls as the grinding medium, grind at a speed of 400r / min for 60min, and grind to obtain a reinforcing material with an average particle size of 40μm.

[0057] A4. Add 20g of reinforcing material to 50mL of anhydrous ethanol and disperse in a high-speed disperser at 2000r / min for 10min to obtain a mixture. Transfer the mixture to a 500mL three-necked flask, add 100g of modified lignin, connect one end of the three-necked flask to a reflux condenser, and then transfer the three-necked flask to a water bath. React at 90℃ for 120min with stirring at 500r / min. After the reaction is complete, filter while hot to obtain a filter cake. Wash the filter cake three times with anhydrous ethanol, then dry and pulverize to obtain composite lignin.

[0058] Example 4

[0059] This embodiment provides a method for preparing antibacterial agent microspheres, including the following steps:

[0060] B1. Mix 10g of sodium dodecyl sulfonate and 100mL of deionized water until completely dissolved to obtain an emulsifier solution; add 100mL of the emulsifier solution, 5g of chlorhexidine and 5-10g of chlorhexidine gluconate to a 250mL three-necked flask, and mix and stir at 100r / min for 5min to obtain intermediate A.

[0061] B2. Add 20g of styrene and 10g of N,N-methylenebisacrylamide to a three-necked flask and mix and stir at 100r / min for 10min to obtain a premix. Then place the three-necked flask in a water bath and set the temperature of the water bath to 80℃. Add 20mL of emulsifier solution dropwise to the three-necked flask using a peristaltic pump. After the addition is complete, continue to stir and react at 80℃ for 2h to obtain an emulsion.

[0062] B3. Dialyze the emulsion, with the dialysis bag retaining a relative molecular weight of 8000-14000 kDa. After separation for 3 days, freeze-dry for 10 hours to obtain a white powder, which is the antibacterial agent microsphere.

[0063] Example 5

[0064] This embodiment provides a method for preparing antibacterial agent microspheres, including the following steps:

[0065] B1. Mix 10g of sodium dodecyl sulfonate and 100mL of deionized water until completely dissolved to obtain an emulsifier solution; add 100mL of the emulsifier solution, 6g of chlorhexidine and 6g of chlorhexidine gluconate to a 250mL three-necked flask, and mix and stir at 100r / min for 8min to obtain intermediate A.

[0066] B2. Add 25g of styrene and 15g of N,N-methylenebisacrylamide to a three-necked flask and mix and stir at 100r / min for 16min to obtain a premix. Then place the three-necked flask in a water bath at 82℃ and add 20mL of emulsifier solution dropwise to the three-necked flask using a peristaltic pump. After the addition is complete, continue stirring and reacting at 83℃ for 2.2h to obtain an emulsion.

[0067] B3. Dialyze the emulsion, with the dialysis bag retaining a relative molecular weight of 8000-14000 kDa. After separation for 3 days, freeze-dry for 11 hours to obtain a white powder, which is the antibacterial agent microsphere.

[0068] Example 6

[0069] This embodiment provides a method for preparing antibacterial agent microspheres, including the following steps:

[0070] B1. Mix 10g of sodium dodecyl sulfonate and 100mL of deionized water until completely dissolved to obtain an emulsifier solution; add 100mL of the emulsifier solution, 10g of chlorhexidine and 10g of chlorhexidine gluconate to a 250mL three-necked flask, and mix and stir at 100r / min for 10min to obtain intermediate A.

[0071] B2. Add 30g of styrene and 20g of N,N-methylenebisacrylamide to a three-necked flask and mix and stir at 100r / min for 20min to obtain a premix. Then place the three-necked flask in a water bath and set the temperature of the water bath to 85℃. Add 20mL of emulsifier solution dropwise to the three-necked flask using a peristaltic pump. After the addition is complete, continue to stir and react at 85℃ for 3h to obtain an emulsion.

[0072] B3. Dialyze the emulsion, with the dialysis bag retaining a relative molecular weight of 8000-14000 kDa. After separation for 3 days, freeze-dry for 12 hours to obtain a white powder, which is the antibacterial agent microsphere.

[0073] Example 7

[0074] This embodiment provides a method for preparing a controlled-release antibacterial packaging film material, including the following steps:

[0075] S1. Weigh 1.5g of crosslinking agent sodium alginate and 200mL of distilled water and add them to a 500mL beaker. Then add 30g of starch, 5g of the composite lignin prepared in Example 1 and 1g of plasticizer glycerin to the beaker. Mix and stir at 100r / min for 10min to prepare a film-forming suspension.

[0076] S2. Add 5g of the antibacterial microspheres prepared in Example 4 to the film-forming suspension, transfer the beaker to a constant temperature water bath, adjust the temperature of the constant temperature water bath to 70℃, stir at 300r / min for 30min to allow it to react and form a uniform film-forming solution.

[0077] S3. The film-forming solution was pre-degassed under a vacuum of 0.09 MPa for 30 min, and then applied at 0.15 g / cm³. 2 The areal density was cast in a petri dish with a diameter of 10 cm, dried in an electric heating oven at 45°C for 6 hours, cooled and peeled off to obtain a controlled-release antibacterial packaging film material.

[0078] Example 8

[0079] This embodiment provides a method for preparing a controlled-release antibacterial packaging film material, including the following steps:

[0080] S1. Weigh 1.8g of crosslinking agent sodium alginate and 200mL of distilled water and add them to a 500mL beaker. Then add 30g of starch, 6g of the composite lignin prepared in Example 2 and 2g of plasticizer glycerin to the beaker. Mix and stir at 100r / min for 10min to prepare a film-forming suspension.

[0081] S2. Add 15g of the antibacterial microspheres prepared in Example 5 to the film-forming suspension, transfer the beaker to a constant temperature water bath, adjust the temperature of the constant temperature water bath to 75℃, and stir at 400r / min for 35min to allow it to react and form a uniform film-forming solution.

[0082] S3. The film-forming solution was pre-degassed under a vacuum of 0.09 MPa for 30 min, and then applied at 0.18 g / cm³. 2 The areal density was cast in a petri dish with a diameter of 10 cm, dried in an electric heating oven at 50°C for 6 hours, cooled and delaminated to obtain a controlled-release antibacterial packaging film material.

[0083] Example 9

[0084] This embodiment provides a method for preparing a controlled-release antibacterial packaging film material, including the following steps:

[0085] S1. Weigh 2g of crosslinking agent sodium alginate and 200mL of distilled water and add them to a 500mL beaker. Then add 30g of starch, 10g of the composite lignin prepared in Example 3 and 5g of plasticizer glycerin to the beaker. Mix and stir at 100r / min for 10min to prepare a film-forming suspension.

[0086] S2. Add 10g of the antibacterial microspheres prepared in Example 6 to the film-forming suspension, transfer the beaker to a constant temperature water bath, adjust the temperature of the constant temperature water bath to 80℃, and stir at 500r / min for 60min to allow it to react and form a uniform film-forming solution.

[0087] S3. The film-forming solution was pre-degassed under a vacuum of 0.09 MPa for 30 min, and then applied at 0.2 g / cm³. 2 The areal density was cast in a petri dish with a diameter of 10 cm, dried in an electric heating oven at 60℃ for 6 hours, cooled and delaminated to obtain a controlled-release antibacterial packaging film material.

[0088] Comparative Example 1

[0089] The difference between this comparative example and Example 9 is that in step 1, the urea-modified lignin was not reacted with (3-isocyanopropyl)triethoxysilane, but was directly compounded with the reinforcing material to obtain modified lignin.

[0090] Comparative Example 2

[0091] The difference between this comparative example and Example 9 is that in step 1, the modified lignin was not combined with the reinforcing material to replace the modified lignin.

[0092] Comparative Example 3

[0093] The difference between this comparative example and Example 9 is that, in step 1, antibacterial microspheres were not added to the film-forming suspension.

[0094] Performance testing:

[0095] 1. In accordance with ASTM D882-02 (2002), the tensile strength and elongation at break of the controlled-release antibacterial packaging film materials prepared in Examples 7-9 and Comparative Examples 1-3 were tested; wherein the initial clamping distance and probe moving speed were set to 50 mm and 1 mm / s, respectively, and each group of samples was measured six times.

[0096] 2. The water vapor transmission coefficient of the controlled-release antibacterial packaging film materials prepared in Examples 7-9 and Comparative Examples 1-3 was determined using a GB1037 cup-type moisture permeability meter; the test area, test temperature and relative humidity were set to 33.0 cm2, 38℃ and 90%, respectively; each group of packaging film materials was tested three times.

[0097] 3. The controlled-release antibacterial packaging film materials prepared in Examples 7-9 and Comparative Examples 1-3 were subjected to an inhibition zone test. The film diameter was 6 mm, and *E. coli* was cultured at 37°C for 24 hours. The area of ​​the inhibition zone was then measured as an indicator of the film's antibacterial activity. Each sample was tested three times. The specific test results are shown in the table below:

[0098] Table 1 - Performance Test Data Table

[0099]

[0100]

[0101] Data Analysis:

[0102] Analysis of the data in Table 1 shows that the controlled-release antibacterial packaging film materials prepared in Examples 7-9 of this invention have excellent mechanical properties, namely good tensile strength and elongation at break. The controlled-release antibacterial packaging film materials prepared in Examples 7-9 of this invention also have excellent waterproof and antibacterial properties, namely low water vapor permeability coefficient and large diameter of inhibition zone for Escherichia coli.

[0103] However, in Comparative Example 1, the urea-modified lignin did not react with (3-isocyanopropyl)triethoxysilane, and in Comparative Example 2, the modified lignin was not combined with the reinforcing material. Both of these reduced the mechanical and waterproof properties of the prepared packaging film material. In Comparative Example 3, the antibacterial microspheres were not added to the film-forming suspension, which reduced its antibacterial efficacy, as evidenced by a significant reduction in the diameter of the Escherichia coli inhibition zone.

[0104] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

[0105] In the description of this specification, references to terms such as "an embodiment," "example," and "specific example" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0106] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a controlled-release antibacterial packaging film material, characterized in that, Includes the following steps: S1, crosslinking agent, distilled water, starch, composite lignin and plasticizer are mixed and stirred to obtain a film-forming suspension, wherein the ratio of crosslinking agent, distilled water, starch, composite lignin and plasticizer is 1.5-2g:200mL:30-40g:5-10g:1-5g; S2. Add antibacterial microspheres to the film-forming suspension and react at 70-80℃ for 30-60 min to obtain the film-forming solution, wherein the amount of antibacterial microspheres is 5-10g; S3. The film-forming solution was degassed under a vacuum of 0.09 MPa for 30 min, and then cast into a petri dish with a surface density of 0.15-2 g / cm2. It was dried at 45-60℃ for 6 h, cooled and peeled off to obtain a controlled-release antibacterial packaging film material. The composite lignin is prepared by the following steps: A1. Mix urea-modified lignin, (3-isocyanopropyl)triethoxysilane and DMF, and react at room temperature for 2-3 hours to obtain modified lignin; A2. Mix fly ash microspheres, wollastonite and dolomite evenly to obtain an inorganic mixture; grind the inorganic mixture to obtain a reinforcing material with an average particle size of 30-40μm; A3. Stir the reinforcing material and anhydrous ethanol at high speed to obtain a mixture; mix the mixture with the modified lignin and react at 80-90℃ for 100-120 min. After the reaction is completed, filter while hot to obtain a filter cake; wash the filter cake three times with anhydrous ethanol, then dry and pulverize to obtain composite lignin. The method for preparing the antibacterial agent microspheres includes the following steps: B1. Sodium dodecyl sulfonate and deionized water are mixed and stirred until completely dissolved to obtain an emulsifier solution; the emulsifier solution, chlorhexidine, and chlorhexidine gluconate are mixed and stirred to obtain intermediate A; B2. Intermediate A, styrene and N,N-methylenebisacrylamide are mixed and stirred to obtain a premix; then an emulsifier solution is added dropwise to the premix. After the addition is complete, the mixture is stirred at 80-85℃ for 2-3 hours to obtain an emulsion. B3. Dialyze the emulsion, with the dialysis bag retaining a relative molecular weight of 8000-14000 kDa. After separation for 3 days, freeze-dry for 10-12 hours to obtain a white powder, which is the antibacterial agent microsphere.

2. The method for preparing a controlled-release antibacterial packaging film material according to claim 1, characterized in that, In step A1, the urea-modified lignin is prepared by the following steps: Formaldehyde was placed in an ice bath at -20°C, followed by the addition of lignin and urea, and the mixture was stirred to obtain a premixed solution. 0.1 mol / L HCl solution was added dropwise to the premixed solution to adjust its pH to 3-4. The premixed solution was reacted at 50-60°C for 2-3 hours, then filtered to obtain a solid. The solid was washed with deionized water and vacuum dried to constant weight to obtain urea-modified lignin.

3. The method for preparing a controlled-release antibacterial packaging film material according to claim 2, characterized in that, The ratio of formaldehyde, lignin and urea used is 30mL:20-30g:5-10g, and the vacuum drying temperature is 60-70℃.

4. The method for preparing a controlled-release antibacterial packaging film material according to claim 1, characterized in that, In step A1, the ratio of urea-modified lignin, (3-isocyanopropyl)triethoxysilane, and DMF is 20-30g:10-20g:200mL; in step A2, the ratio of fly ash microspheres, wollastonite, and dolomite is 10-20g:10g:10g; the grinding media is zirconia balls, the grinding speed is 200-400r / min, and the grinding time is 30-60min; in step A3, the ratio of reinforcing material to anhydrous ethanol is 20g:50mL, and the amount of modified lignin is 80-100g.

5. The method for preparing a controlled-release antibacterial packaging film material according to claim 1, characterized in that, In step B1, the ratio of sodium dodecyl sulfonate to deionized water is 10g:100mL, and the ratio of chlorhexidine to chlorhexidine gluconate is 5-10g:5-10g; in step B2, the ratio of styrene to N,N-methylenebisacrylamide is 20-30g:10-20g.

6. The method for preparing a controlled-release antibacterial packaging film material according to claim 1, characterized in that, In step S1, the crosslinking agent is sodium alginate and the plasticizer is glycerol; the mixing speed is 100 r / min and the mixing time is 10 min.

7. A controlled-release antibacterial packaging film material, characterized in that, The controlled-release antibacterial packaging film material is prepared using the method described in any one of claims 1-6.

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