Chitosan-based antibacterial wrapping film as well as preparation method and application thereof

Abstract

The invention relates to the technical field of winding packaging, and provides a chitosan-based antibacterial winding film as well as a preparation method and application thereof. The preparation method comprises the following steps: aminating the C-6 site of chitosan, synthesizing aminated chitosan, carrying out carboxylation modification on-OH on polyvinyl alcohol to obtain carboxylated polyvinyl alcohol, and crosslinking the aminated chitosan and the carboxylated polyvinyl alcohol through a multi-aldehyde crosslinking agent to obtain the chitosan-based antibacterial wrapping film. Chitosan from non-grain biomass is used as a base material, and the chitosan-based antibacterial wrapping film integrating three functions of high stretching rate, self-adhesion and antibiosis is prepared through the synergistic effect of two different types of dynamic bonds (dynamic ionic hydrogen bonds and dynamic imine bonds). The method has important significance for solving the problems of the traditional petroleum-based wrapping film and the bacterial pollution problem in the packaging industry.

Description

Technical Field

[0001] The present invention relates to the technical field of wrapping packaging, and in particular to a chitosan-based antibacterial wrapping film and a preparation method and application thereof. Background Art

[0002] Wrap wrapping is a packaging technology that uses stretch film as its primary material. The film is wrapped mechanically or manually around the outside of the goods to create a tight package. Its core principle is to utilize the film's elasticity to secure, protect, and containerize goods. It is widely used in logistics, warehousing, and industrial production. Traditional stretch film is petroleum-based, typically made from polyethylene (PE). Petroleum-based stretch film is derived from non-renewable petroleum resources, is difficult to degrade naturally, and lacks inherent antimicrobial properties, making it difficult to meet the demands of green and antimicrobial packaging.

[0003] Chitosan (CS), derived from non-food biomass, holds significant promise for applications in green, antimicrobial packaging. However, chitosan's rigid structure, characterized by a large number of six-membered rings, renders it brittle and results in a low stretchability after film formation, severely hindering its application in wrapping packaging. While the introduction of plasticizers and self-adhesives is a common method for improving the stretchability of chitosan-based films, migration of these agents is a significant concern. During packaging application, these agents may leach from the film and migrate into the package contents, impacting product quality and posing a health and safety risk.

[0004] The currently reported chitosan-based film materials have a low stretch ratio (basically around 50%) and lack adhesion, which is far from meeting the two hard index requirements of stretchability (stretch ratio ≥ 300%) and self-adhesion (adhesion force ≥ 2N) for stretch film in the field of wrapping packaging, and it is difficult to meet application requirements. Summary of the Invention

[0005] In view of this, the present invention provides a chitosan-based antibacterial stretch film, its preparation method, and application. The present invention improves the stretching ratio and self-adhesion of the chitosan-based film material by constructing a dynamic polymer network, thereby enhancing its applicability in the field of wrapping packaging.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A method for preparing a chitosan-based antibacterial stretch film comprises the following steps:

[0008] methanesulfonic acid, chitosan and acryloyl chloride are mixed to carry out acylation reaction to obtain acryloyl chitosan;

[0009] The acryloyl chitosan, a bifunctional modifier containing a thiol group and an amino group, a photoinitiator and water are mixed to carry out a thiol-ene click chemistry reaction to obtain amino chitosan;

[0010] polyvinyl alcohol, dianhydride, triethylamine and a solvent are mixed to perform a carboxylation reaction to obtain carboxylated polyvinyl alcohol;

[0011] The amino chitosan, carboxylated polyvinyl alcohol, a polyaldehyde crosslinking agent and water are mixed to obtain a casting solution; based on the total mass of the amino chitosan and carboxylated polyvinyl alcohol being 100%, the mass fraction of the carboxylated polyvinyl alcohol is greater than 20%;

[0012] The casting solution is subjected to film forming to obtain the chitosan-based antibacterial stretch film.

[0013] Preferably, the ratio of chitosan to acryloyl chloride is 1 g:3-5 mL; the ratio of methanesulfonic acid to chitosan is 5-10 mL:1 g;

[0014] The temperature of the acylation reaction is 0-5° C., and the time is 5-10 hours.

[0015] Preferably, the bifunctional modifier containing a thiol group and an amino group includes one or more of mercaptoethylamine, mercaptopropylamine and mercaptobutylamine; the mass ratio of the acryloyl chitosan to the bifunctional modifier containing a thiol group and an amino group is 1:1 to 2; the photoinitiator is 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone; the mass ratio of the acryloyl chitosan to the photoinitiator is 20:1 to 5.

[0016] Preferably, the thiol-ene click chemistry reaction is carried out under ultraviolet light irradiation, and the time of the thiol-ene click chemistry reaction is 1 to 3 hours.

[0017] Preferably, the dianhydride comprises one or more of oxalic anhydride, malonic anhydride and succinic anhydride; the mass ratio of the polyvinyl alcohol to the dianhydride is 2 to 5:1;

[0018] The carboxylation reaction time is 12 to 36 hours.

[0019] Preferably, the number of aldehyde groups in the polyaldehyde cross-linking agent is greater than or equal to 2; and the mass ratio of the amino chitosan to the polyaldehyde cross-linking agent is 10:1-3.

[0020] Preferably, based on the total mass of the amino chitosan and the carboxylated polyvinyl alcohol being 100%, the mass fraction of the carboxylated polyvinyl alcohol is greater than 20% and less than or equal to 50%.

[0021] Preferably, the film forming comprises: adding the casting solution into a mold, and then drying; the drying temperature is 50-80°C.

[0022] The present invention also provides a chitosan-based antibacterial stretch film prepared by the preparation method described in the above scheme.

[0023] The present invention also provides the application of the chitosan-based antibacterial stretch film described in the above solution in the field of stretch packaging.

[0024] The invention provides a preparation method of a chitosan-based antibacterial stretch film, comprising the following steps: mixing methanesulfonic acid, chitosan and acryloyl chloride to carry out an acylation reaction to obtain acryloyl chitosan; mixing the acryloyl chitosan, a bifunctional modifier containing a thiol group and an amino group, a photoinitiator and water to carry out a thiol-ene click chemical reaction to obtain amino chitosan; mixing polyvinyl alcohol, dianhydride, triethylamine and a solvent to carry out a carboxylation reaction to obtain carboxylated polyvinyl alcohol; mixing the amino chitosan, carboxylated polyvinyl alcohol, a polyaldehyde crosslinking agent and water to obtain a casting solution; based on the total mass of the amino chitosan and the carboxylated polyvinyl alcohol being 100%, the mass fraction of the carboxylated polyvinyl alcohol is greater than 20%; and forming a film from the casting solution to obtain the chitosan-based antibacterial stretch film. The present invention uses chitosan as the starting raw material, and starting from the molecular modification design of the raw material, the C-6 position of chitosan is aminated to synthesize amino-chitosan; at the same time, the -OH on polyvinyl alcohol is carboxylated to obtain carboxylated polyvinyl alcohol; the amino-chitosan and carboxylated polyvinyl alcohol are then cross-linked to form a film through a polyaldehyde cross-linking agent. During the cross-linking process, the amino groups of the amino-chitosan react with the polyaldehyde cross-linking agent to produce dynamic imine bonds, and at the same time, dynamic ionic hydrogen bonds are formed between the amino groups of the amino-chitosan and the carboxyl groups of the carboxylated polyvinyl alcohol. Through the synergistic effect of two different types of dynamic bonds (dynamic ionic hydrogen bonds and dynamic imine bonds), a chitosan-based antibacterial stretch film that combines the three functions of "high stretch ratio", "self-adhesion" and "antibacterial" is prepared. In summary, the chitosan-based antibacterial stretch film prepared by the present invention has the following beneficial effects:

[0025] (1) High stretching ratio: The chitosan-based antibacterial stretch film of the present invention has a dual dynamic network structure, in which there are two different types of strong and weak dynamic bonds, imine bonds and ionic hydrogen bonds. A small amount of strong imine bonds maintains the integrity of the network during the stretching process of the film material, while a large amount of weak ionic hydrogen bonds consume energy during the stretching process, so that the film material can obtain a high stretching ratio (stretching ratio ≥300%).

[0026] (2) Good self-adhesion: During the stretching process of the film material, some dynamic bonds of the stretching interface will break. When the two stretched interfaces come into contact with each other again, these broken dynamic bonds will quickly reorganize and regenerate, so that the film material in the stretch wrapping process can achieve self-adhesion without adding self-adhesive (adhesion force ≥ 2N);

[0027] (3) Good antibacterial property: On the basis of chitosan’s own antibacterial property, the antibacterial property of chitosan-based wrapping film can be enhanced by introducing -NH2 after directional structural modification of -OH at the C-6 position of chitosan;

[0028] (4) Green and environmentally friendly: The chitosan-based antibacterial wrapping film of the present invention uses chitosan as the main raw material, has good degradability, and is green and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A flow chart for preparing the chitosan-based antibacterial stretch film provided by the present invention;

[0030] Figure 2 This is the synthetic route of amino chitosan;

[0031] Figure 3 This is a synthetic route for carboxylated polyvinyl alcohol;

[0032] Figure 4 Schematic diagram of the wrapping packaging test of the chitosan-based antibacterial wrapping film in the embodiment. DETAILED DESCRIPTION

[0033] The present invention provides a method for preparing a chitosan-based antibacterial stretch film, comprising the following steps:

[0034] methanesulfonic acid, chitosan and acryloyl chloride are mixed to carry out acylation reaction to obtain acryloyl chitosan;

[0035] The acryloyl chitosan, a bifunctional modifier containing a thiol group and an amino group, a photoinitiator and water are mixed to carry out a thiol-ene click chemistry reaction to obtain amino chitosan;

[0036] polyvinyl alcohol, dianhydride, triethylamine and a solvent are mixed to perform a carboxylation reaction to obtain carboxylated polyvinyl alcohol;

[0037] The amino chitosan, carboxylated polyvinyl alcohol, a polyaldehyde crosslinking agent and water are mixed to obtain a casting solution; based on the total mass of the amino chitosan and carboxylated polyvinyl alcohol being 100%, the mass fraction of the carboxylated polyvinyl alcohol is greater than 20%;

[0038] The casting solution is subjected to film forming to obtain the chitosan-based antibacterial stretch film.

[0039] Figure 1The preparation flow chart of the chitosan-based antibacterial stretch film provided by the present invention is as follows: Figure 1 Provide detailed explanation.

[0040] The present invention mixes methanesulfonic acid, chitosan (CS) and acryloyl chloride for an acylation reaction to obtain acryloyl chitosan (CS-AC). In the present invention, the amount ratio of methanesulfonic acid to chitosan is preferably 5-10 mL:1 g, specifically 9 mL:1 g; the methanesulfonic acid serves as a solvent, catalyst and amino protective agent for the reaction, protecting the amino group at the C-2 position of chitosan and enabling the -OH group at the C-6 position of chitosan to be directionally amino-modified; the amount ratio of chitosan to acryloyl chloride is preferably 1 g:3-5 mL, specifically 1 g:3.75 mL; the temperature of the acylation reaction is preferably 0-5°C, and the time of the acylation reaction is preferably 5-10 hours, specifically 8 hours; the acylation reaction is preferably carried out under stirring; and the acylation reaction occurs at the -OH group at the C-6 position of chitosan.

[0041] After the acylation reaction is completed, the present invention preferably performs post-treatment on the obtained reaction solution; the post-treatment preferably includes: 1) pouring the reaction solution into an ether-acetone mixture and letting it stand, then removing the supernatant to obtain a lower precipitate; centrifuging the lower precipitate to obtain a crude product; 2) dissolving the crude product with methanol to obtain a dissolving solution; treating the dissolving solution according to the method of step 1) to obtain a solid product; 3) washing the solid product with ether, vacuum drying and grinding to obtain acryloyl chitosan; the volume ratio of ether to acetone in the ether-acetone mixture is preferably 1:1; the amount ratio of the chitosan to the ether-acetone mixture is preferably 4g:500mL; and the standing time is preferably 30min.

[0042] After obtaining the acryloyl chitosan, the present invention mixes the acryloyl chitosan, a bifunctional modifier containing a thiol group and an amino group, a photoinitiator, and water to perform a thiol-ene click chemistry reaction to obtain amino chitosan (CS-AC-NH2). In the present invention, the bifunctional modifier containing a thiol group and an amino group preferably includes one or more of mercaptoethylamine (β-mercaptoethylamine), mercaptopropylamine, and mercaptobutylamine, more preferably mercaptoethylamine; the mass ratio of the acryloyl chitosan to the bifunctional modifier containing a thiol group and an amino group is preferably 1:1-2, specifically 1:1.5; the photoinitiator is preferably 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone; the mass ratio of the acryloyl chitosan to the photoinitiator is preferably 20:1-5, specifically 20:3; the amount ratio of the acryloyl chitosan to water is preferably 1 g:20-30 mL, specifically 1 g:25 mL.

[0043] In the present invention, the thiol-ene click chemistry reaction is preferably carried out under ultraviolet light irradiation, the wavelength of the ultraviolet light is 365nm, and the time of the thiol-ene click chemistry reaction is preferably 1 to 3 hours, specifically 1 hour. In the present invention, the synthetic route of the amino chitosan is as follows Figure 2 shown.

[0044] After the thiol-ene click chemistry reaction is completed, the present invention preferably performs post-treatment on the obtained reaction solution; the post-treatment preferably comprises: pouring the reaction solution into acetone and letting it stand to precipitate a solid, then filtering to obtain a solid product, washing the solid product with ether, and then drying and grinding in sequence to obtain amino chitosan; the ratio of the acryloyl chitosan to acetone is preferably 2g:150mL; and the standing time is preferably 30min.

[0045] The present invention mixes polyvinyl alcohol, dianhydride, triethylamine and solvent for carboxylation reaction to obtain carboxylated polyvinyl alcohol (PVA-COOH). In the present invention, the dianhydride preferably includes one or more of oxalic anhydride, malonic anhydride and succinic anhydride, more preferably succinic anhydride; the mass ratio of the polyvinyl alcohol and the dianhydride is preferably 2 to 5:1, specifically 4:1; the mass ratio of the triethylamine and the dianhydride is preferably 1:1 to 1.5, more preferably 1:1; the solvent is preferably dimethyl sulfoxide (DMSO); the mass ratio of the solvent and polyvinyl alcohol is preferably 200 to 300 g:20 mL, specifically 250 g:20 mL; the temperature of the carboxylation reaction is preferably room temperature, and the reaction time is preferably 12 to 36 h, specifically 24 h; the carboxylation reaction is preferably carried out under stirring; in the carboxylation reaction, the hydroxyl groups in the polyvinyl alcohol react with the dianhydride to generate carboxylated polyvinyl alcohol; the reaction formula of the carboxylation reaction is as follows Figure 3 After the carboxylation reaction is completed, the present invention preferably uses a dialysis bag to perform a dialysis purification treatment on the reaction solution to obtain carboxylated polyvinyl alcohol.

[0046] After obtaining amino chitosan and carboxylated polyvinyl alcohol, the present invention mixes the amino chitosan, carboxylated polyvinyl alcohol, a polyaldehyde crosslinking agent and water to obtain a casting solution. In the present invention, the number of aldehyde groups in the polyaldehyde crosslinking agent is preferably greater than or equal to 2, specifically 2 to 3; the polyaldehyde crosslinking agent preferably includes one or more of glutaraldehyde and trimesic acid; the mass ratio of the amino chitosan to the polyaldehyde crosslinking agent is preferably 10:1 to 3, specifically 10:1, 10:2 or 10:3. The polyaldehyde crosslinking agent can react with the amino groups of the amino chitosan to produce dynamic imine bonds, thereby regulating the ratio of dynamic imine bonds to dynamic ionic hydrogen bonds. In the present invention, amino groups and carboxyl groups can form dynamic ionic hydrogen bonds, and amino groups and aldehyde groups can form dynamic imine bonds. The present invention controls the molar ratio of amino chitosan to polyaldehyde crosslinking agent within the above range, so that the ionic hydrogen bonds in the obtained chitosan-based antibacterial stretch film account for the majority (70-90%) and the imine bonds account for the minority (10-30%), thereby ensuring that the film has excellent tensile properties and self-adhesive properties.

[0047] In the present invention, based on the total mass of the amino chitosan and carboxylated polyvinyl alcohol as 100%, the mass of the carboxylated polyvinyl alcohol is greater than 20%, preferably greater than 20% and less than or equal to 50%, specifically 25%, 30%, 40% or 50%.

[0048] In a specific embodiment of the present invention, preferably, amino chitosan and carboxylated polyvinyl alcohol are first dissolved in water at room temperature to obtain an amino chitosan aqueous solution and a carboxylated polyvinyl alcohol aqueous solution; the carboxylated polyvinyl alcohol aqueous solution is then added dropwise to the amino chitosan aqueous solution under stirring, and then a polyaldehyde crosslinking agent is added to obtain a casting solution. In the present invention, in order to prevent the amino chitosan and carboxylated polyvinyl alcohol from forming ionic hydrogen bonds too quickly and causing precipitation, a small amount of acid solution is preferably added dropwise to the system to provide an acidic environment; the acid solution is preferably 5wt% hydrochloric acid; and the pH value of the casting solution is preferably 4-7.

[0049] After obtaining the casting solution, the present invention preferably performs ultrasonic debubbling on the casting solution before forming the film, and the time for the ultrasonic debubbling is preferably 30 minutes.

[0050] After obtaining the casting solution, the present invention forms a film from the casting solution to produce the chitosan-based antimicrobial stretch film. In the present invention, the film formation preferably includes: adding the casting solution to a mold and then drying it; the mold depth is preferably 3 mm; and the drying temperature is preferably 50-80°C, specifically 60°C. During the film formation process, the amino groups of the amino-modified chitosan react with the polyaldehyde crosslinker to produce dynamic imine bonds. Simultaneously, dynamic ionic hydrogen bonds form between the amino groups of the amino-modified chitosan and the carboxyl groups of the carboxylated polyvinyl alcohol, thereby forming a dual dynamic network structure.

[0051] After drying, the present invention preferably soaks the resulting dry film in an alkaline solution, then soaks and washes it with deionized water until it becomes neutral, and then dries it again to obtain a chitosan-based antibacterial stretch film; the alkaline solution is preferably an aqueous sodium hydroxide solution; the pH value of the aqueous sodium hydroxide solution is preferably 10 to 12, more preferably 12. The present invention can neutralize the residual acid in the dry film by soaking in the alkaline solution.

[0052] The present invention also provides a chitosan-based antimicrobial stretch film prepared by the method described above; the chitosan-based antimicrobial stretch film is cross-linked with amino-modified chitosan and carboxylated polyvinyl alcohol. In the present invention, the chitosan-based antimicrobial stretch film has a strength of ≥40 MPa, specifically 40.18 to 63.38 MPa, an elongation at break of ≥300%, preferably ≥320%, specifically 324.84 to 463.87%, and an adhesive strength of ≥2 N, preferably ≥4 N, specifically 4.37 to 5.14 N.

[0053] The present invention also provides the application of the chitosan-based antibacterial stretch film described in the above solution in the field of stretch packaging. The chitosan-based antibacterial stretch film provided by the present invention has good stretchability and self-adhesion, as well as excellent antibacterial properties, and has broad application prospects in the field of stretch packaging.

[0054] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0055] Example 1

[0056] (1) 180 mL of methanesulfonic acid was added to a reaction flask, and 20 g of chitosan and 75 mL of acryloyl chloride were added. The mixture was stirred at 0°C for 8 h. After the reaction was completed, the reaction solution was slowly poured into 2500 mL of ether-acetone mixture (the volume ratio of ether to acetone was 1:1). After standing for 30 min, the supernatant was poured out and the precipitate was centrifuged at 5000 rpm for 2 min to obtain a crude product. The crude product was dissolved in methanol and then repeatedly added to the ether-acetone mixture for standing and centrifugation to obtain a white solid. The white solid was washed with ether three times and then vacuum dried for 10 h. The solid was ground and weighed to obtain a yellow solid acryloyl (C-6) chitosan.

[0057] 500 mL of water was added to a reaction flask, and 20 g of acryloyl (C-6) chitosan, 30 g of β-mercaptoethylamine, and 3 g of photoinitiator 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone were added. The thiol-ene click chemistry reaction was carried out under 365 nm ultraviolet light irradiation for 1 hour. After the reaction, the reaction solution was slowly poured into 1500 mL of acetone to precipitate a white solid. The solution was stirred evenly and allowed to stand for 30 minutes. After the standing period, the solution was filtered with a Buchner funnel to obtain a white solid. The obtained white solid was washed with ether three times, dried, and then ground to obtain amino (C-6) chitosan (CS-AC-NH2).

[0058] (2) Dissolve 22 g of polyvinyl alcohol in 250 mL of anhydrous dimethyl sulfoxide at 60°C. After complete dissolution, cool the solution to room temperature. Add 5 g of succinic anhydride (modifier) ​​and 5 g of triethylamine (catalyst) to the system in sequence at room temperature. Continue the reaction for 24 h. The reaction solution is dialyzed and purified using a dialysis bag to obtain carboxylated polyvinyl alcohol (PVA-COOH).

[0059] (3) At room temperature, amino (C-6 position) chitosan and carboxylated polyvinyl alcohol are dissolved in water to obtain a 5 wt% aqueous solution of amino (C-6 position) chitosan and a 5 wt% aqueous solution of carboxylated polyvinyl alcohol. At room temperature, the 5 wt% aqueous solution of carboxylated polyvinyl alcohol is added dropwise to the 5 wt% aqueous solution of amino (C-6 position) chitosan under stirring, and trimesic acid is added simultaneously (the mass ratio of amino chitosan to trimesic acid is 10:2) to form a casting solution, wherein the mass ratio of amino (C-6 position) chitosan to carboxylated polyvinyl alcohol is 70:30; 5 wt% hydrochloric acid is added to the casting solution to adjust the pH value to 5.

[0060] (4) The casting liquid was ultrasonically treated for 30 minutes to remove bubbles, and then injected into a 3 mm deep mold and placed horizontally in a drying oven at 60 ° C to dry and form a film. After the film was formed, it was immersed in alkaline solution (sodium hydroxide aqueous solution, pH value 12), and then immersed in deionized water and washed until neutral. After drying, the chitosan-based antibacterial wrapping film was obtained.

[0061] Performance testing:

[0062] Tensile strength and elongation at break: The tensile strength and elongation at break of the chitosan-based antibacterial wrapping film were tested according to ASTM D882-02. The specific test results are as follows: tensile strength of 63.38 MPa, elongation at break of 324.84%. Adhesion test: After two 1-cm-wide film materials were subjected to a pressure of 1 MPa for 30 seconds, the tearing force required to separate the two films was tested. The results showed that the adhesion force was 4.37 N.

[0063] Antibacterial performance test: The antibacterial performance of the obtained chitosan-based antibacterial stretch film was tested using the colony counting method. The specific test method is as follows:

[0064] Preparation of bacterial suspension: Prior to the antibacterial test, foodborne pathogens (S. aureus and E. coli) were inoculated into Erlenmeyer flasks containing LB broth, sealed with parafilm, and cultured in a constant-temperature shaker (150 rpm) in a water bath. S. aureus and E. coli were incubated at 37°C for 24 hours to obtain a bacterial suspension. All experimental supplies (except the bacteria) were sterilized by UV or autoclaving.

[0065] Antibacterial test: The antibacterial performance of the membrane samples was studied by colony counting method. The colony concentration of the two bacterial suspensions was diluted to 10 with sterile PBS buffer solution with pH = 7.4. 6 CFU·mL -1 Take 10mL of Staphylococcus aureus (10 6 CFU·mL -1 ) and Escherichia coli (10 6 CFU·mL -1 ) of bacterial solution and 30×30mm 2 Film samples (cut into about 100mm 2 After mixing, the mixture was placed in a constant temperature water bath oscillator (150 rpm), and the Staphylococcus aureus and Escherichia coli liquids were exposed at 37°C for 24 hours. After the bacterial suspension after the sample was exposed was diluted 10,000 times with a sterile PBS buffer solution with a pH of 7.4, 0.1 mL was evenly spread on the LB solid culture medium, sealed with a sealing film, and placed upside down in a biochemical incubator for culture (cultured at 37°C for 24 hours). The test without adding the membrane sample was the blank group, and the test with the membrane sample was the test group. The number of colonies on the solid culture medium was counted, and the antibacterial rate was calculated according to formula (1). Five parallel samples were taken for each group of experiments.

[0066] Bacterial inhibition rate (%) = 100% × (BE) / B (1)

[0067] In formula (1), B is the number of colonies in the blank group, and E is the number of colonies in the test group.

[0068] The test results show that the chitosan-based antibacterial stretch film has an antibacterial rate of 99.01% against Staphylococcus aureus and 99.25% against Escherichia coli.

[0069] Example 2

[0070] Other conditions were the same as those in Example 1, except that the mass ratio of amino (C-6 position) chitosan to carboxylated polyvinyl alcohol was controlled to be 60:40 during the preparation of the casting solution.

[0071] According to the method in Example 1, the tensile strength, elongation at break, adhesion, and antibacterial rate of the obtained chitosan-based antibacterial stretch film were tested, and the results were as follows: tensile strength was 52.86 MPa, elongation at break was 397.65%, adhesion was 4.84 N, antibacterial rate against Staphylococcus aureus was 96.33%, and antibacterial rate against Escherichia coli was 97.54%.

[0072] Example 3

[0073] Other conditions were the same as those in Example 1, except that the mass ratio of amino (C-6 position) chitosan to carboxylated polyvinyl alcohol was controlled to be 50:50 during the preparation of the casting solution.

[0074] According to the method in Example 1, the tensile strength, elongation at break, adhesion and antibacterial rate of the obtained chitosan-based antibacterial stretch film were tested, and the results were as follows: tensile strength was 40.18 MPa, elongation at break was 463.87%, adhesion was 5.14 N, antibacterial rate against Staphylococcus aureus was 92.76%, and antibacterial rate against Escherichia coli was 93.46%.

[0075] From the mechanical property results, the stretching ratio and adhesion of the chitosan-based antibacterial stretch films prepared in Examples 1 to 3 meet the requirements of stretchability (stretching ratio ≥ 300%) and self-adhesion (adhesion ≥ 2N) in the field of wrapping packaging.

[0076] In addition, the barrier properties and wrapping packaging properties of the chitosan-based antibacterial wrapping films prepared in Examples 1 to 3 were tested, as follows:

[0077] Water Vapor Barrier Test: The water vapor permeability (WVP) of the film samples was measured using the cup method. A glass test cup (40 mm diameter, 25 mm depth) was filled with 20 mL of deionized water, and the cut chitosan-based antimicrobial stretch film was sealed with wax on top of the glass test cup (effective diameter 34 mm). The sealed cup was placed in a controlled incubator (25°C, 50% RH) until the water loss in the cup became constant. The water evaporation rate was recorded every 24 hours. The WVP of the chitosan-based antimicrobial stretch film sample was calculated according to formula (2). Five parallel samples of each film were tested.

[0078] WVP(g·Pa ﹣1 ·s ﹣1 ·m ﹣1 )=(Δw×L) / (Δt×A×Δp) (2)

[0079] In formula (2), Δw / Δt(g·s -1 ) is the slope of the amount of water vapor passing through the membrane versus time; L(m) is the thickness of the membrane; A(m 2 ) is the effective area of ​​the membrane through which water vapor passes; Δp (Pa) is the water vapor pressure difference on both sides of the membrane under the test conditions.

[0080] The test results show that under the environment of 25℃ and 50%RH, the water vapor transmission rate of the chitosan-based antibacterial stretch films prepared in Examples 1 to 3 is between 1.2 and 1.8×10 -9 g Pa -1 s -1 m -1 When the mass ratio of amino (C-6 position) chitosan to carboxylated polyvinyl alcohol is 70:30 (i.e., Example 1), the barrier performance of the obtained chitosan-based antibacterial stretch film is the best.

[0081] Wrapping packaging: Cut the chitosan-based antibacterial wrapping film into 2×5cm strip samples, and use it to wrap multiple pencils (take 3 pencils as an example). The wrapping packaging process is as follows: Figure 4 The results show that after the chitosan-based antibacterial wrapping film prepared in Examples 1 to 3 was wrapped around three pencils for four times, the film sample could be automatically sealed and did not fall apart, indicating that it had good wrapping packaging performance.

[0082] Comparative Example 1

[0083] Other conditions were the same as those in Example 1, except that the mass ratio of amino (C-6 position) chitosan to carboxylated polyvinyl alcohol was controlled to be 90:10 during the preparation of the casting solution.

[0084] According to the method in Example 1, the tensile strength, elongation at break, adhesion, and antibacterial rate of the obtained chitosan-based antibacterial stretch film were tested, and the results were as follows: tensile strength was 41.77 MPa, elongation at break was 51.91%, adhesion was 2.42 N, antibacterial rate against Staphylococcus aureus was 78.97%, and antibacterial rate against Escherichia coli was 82.04%.

[0085] Comparative Example 2

[0086] Other conditions were the same as those in Example 1, except that the mass ratio of amino (C-6 position) chitosan to carboxylated polyvinyl alcohol was controlled to be 80:20 during the preparation of the casting solution.

[0087] According to the method in Example 1, the tensile strength, elongation at break, adhesion, and antibacterial rate of the obtained chitosan-based antibacterial stretch film were tested, and the results were as follows: tensile strength was 60.07 MPa, elongation at break was 196.77%, adhesion was 3.89 N, antibacterial rate against Staphylococcus aureus was 93.88%, and antibacterial rate against Escherichia coli was 95.75%.

[0088] According to the results of Comparative Examples 1 and 2, it can be seen that when the amount of carboxylated polyvinyl alcohol is reduced, the tensile properties of the resulting stretch film decrease, and the elongation at break cannot meet the requirement of ≥300%.

[0089] Comparative Example 3

[0090] Other conditions were the same as those in Example 1, except that the mass ratio of amino (C-6 position) chitosan to carboxylated polyvinyl alcohol was controlled to be 100:0 when preparing the casting solution, i.e., carboxylated polyvinyl alcohol was omitted, and 5 wt% amino chitosan solution was directly used to add the crosslinker for reaction.

[0091] The tensile strength, elongation at break, adhesion, and antibacterial rate of the resulting chitosan-based antibacterial stretch film were tested using the method described in Example 1. The results were as follows: tensile strength of 31.37 MPa, elongation at break of 6.39%, adhesion of 0.58 N, antibacterial rates against Staphylococcus aureus of 66.49%, and antibacterial rates against Escherichia coli of 75.10%. The test results of Comparative Example 1 indicate that omitting the carboxylated polyvinyl alcohol significantly reduces the tensile, adhesion, and antibacterial properties of the resulting chitosan-based antibacterial stretch film.

[0092] In summary, the present invention addresses the problems of traditional petroleum-based stretch film materials in terms of non-renewable raw materials, degradation, self-adhesiveness, and antibacterial properties. Chitosan derived from non-food biomass is used as the base material, and two strong and weak dynamic bonds (dynamic ionic hydrogen bonds and dynamic imine bonds) are constructed to prepare a chitosan-based antibacterial stretch film with a dual dynamic network structure. The resulting stretch film has a high stretch ratio, good self-adhesive properties, and good antibacterial properties. This is of great significance for solving the problems of traditional petroleum-based stretch films and the bacterial contamination problem in the packaging industry.

[0093] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a chitosan-based antibacterial stretch film, characterized in that: The following steps are involved: methanesulfonic acid, chitosan and acryloyl chloride are mixed to carry out acylation reaction to obtain acryloyl chitosan; The acryloyl chitosan, a bifunctional modifier containing a thiol group and an amino group, a photoinitiator and water are mixed to carry out a thiol-ene click chemistry reaction to obtain amino chitosan; polyvinyl alcohol, dianhydride, triethylamine and a solvent are mixed to perform a carboxylation reaction to obtain carboxylated polyvinyl alcohol; The amino chitosan, carboxylated polyvinyl alcohol, a polyaldehyde crosslinking agent and water are mixed to obtain a casting solution; based on the total mass of the amino chitosan and carboxylated polyvinyl alcohol being 100%, the mass fraction of the carboxylated polyvinyl alcohol is greater than 20%; The casting solution is subjected to film forming to obtain the chitosan-based antibacterial stretch film.

2. The preparation method according to claim 1, characterized in that The ratio of chitosan to acryloyl chloride is 1 g: 3-5 mL; the ratio of methanesulfonic acid to chitosan is 5-10 mL: 1 g; The temperature of the acylation reaction is 0-5° C., and the time is 5-10 hours.

3. The preparation method according to claim 1, characterized in that The bifunctional modifier containing a thiol group and an amino group includes one or more of mercaptoethylamine, mercaptopropylamine and mercaptobutylamine; the mass ratio of the acryloyl chitosan to the bifunctional modifier containing a thiol group and an amino group is 1:1 to 2; the photoinitiator is 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone; and the mass ratio of the acryloyl chitosan to the photoinitiator is 20:1 to 5.

4. The preparation method according to claim 1, characterized in that The thiol-ene click chemistry reaction is carried out under ultraviolet light irradiation, and the time of the thiol-ene click chemistry reaction is 1 to 3 hours.

5. The preparation method according to claim 1, characterized in that The dianhydride includes one or more of oxalic anhydride, malonic anhydride and succinic anhydride; the mass ratio of the polyvinyl alcohol to the dianhydride is 2 to 5:1; The carboxylation reaction time is 12 to 36 hours.

6. The preparation method according to claim 1, characterized in that The number of aldehyde groups in the multi-aldehyde cross-linking agent is greater than or equal to 2; the mass ratio of the amino chitosan to the multi-aldehyde cross-linking agent is 10:1-3.

7. The preparation method according to claim 1, characterized in that Taking the total mass of the amino chitosan and the carboxylated polyvinyl alcohol as 100%, the mass fraction of the carboxylated polyvinyl alcohol is greater than 20% and less than or equal to 50%.

8. The preparation method according to claim 1, characterized in that The film forming comprises: adding the casting liquid into a mold and then drying it; the drying temperature is 50-80°C.

9. Chitosan-based antibacterial stretch film prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the chitosan-based antibacterial stretch film according to claim 9 in the field of stretch wrapping.

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