CN112623500A - Sandwich-shaped chitosan-based antibacterial composite film with nano-silver fixed by reduced graphene oxide for food packaging and preparation method and application thereof - Google Patents

Sandwich-shaped chitosan-based antibacterial composite film with nano-silver fixed by reduced graphene oxide for food packaging and preparation method and application thereof Download PDF

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CN112623500A
CN112623500A CN202011425688.XA CN202011425688A CN112623500A CN 112623500 A CN112623500 A CN 112623500A CN 202011425688 A CN202011425688 A CN 202011425688A CN 112623500 A CN112623500 A CN 112623500A
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silver
graphene oxide
chitosan
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CN112623500B (en
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王小英
顾彬
蒋启蒙
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South China University of Technology SCUT
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
    • B65D65/00—Wrappers or flexible covers; Packaging materials of special type or form
    • B65D65/38—Packaging materials of special type or form
    • B65D65/46—Applications of disintegrable, dissolvable or edible materials
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
    • B65D—CONTAINERS FOR STORAGE OR TRANSPORT OF ARTICLES OR MATERIALS, e.g. BAGS, BARRELS, BOTTLES, BOXES, CANS, CARTONS, CRATES, DRUMS, JARS, TANKS, HOPPERS, FORWARDING CONTAINERS; ACCESSORIES, CLOSURES, OR FITTINGS THEREFOR; PACKAGING ELEMENTS; PACKAGES
    • B65D81/00—Containers, packaging elements, or packages, for contents presenting particular transport or storage problems, or adapted to be used for non-packaging purposes after removal of contents
    • B65D81/24—Adaptations for preventing deterioration or decay of contents; Applications to the container or packaging material of food preservatives, fungicides, pesticides or animal repellants
    • B65D81/28—Applications of food preservatives, fungicides, pesticides or animal repellants
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/18—Manufacture of films or sheets
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2305/00—Characterised by the use of polysaccharides or of their derivatives not provided for in groups C08J2301/00 or C08J2303/00
    • C08J2305/08—Chitin; Chondroitin sulfate; Hyaluronic acid; Derivatives thereof
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/08—Metals
    • C08K2003/0806—Silver
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K2201/00—Specific properties of additives
    • C08K2201/011—Nanostructured additives
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/04—Carbon
    • C08K3/042—Graphene or derivatives, e.g. graphene oxides
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K9/00—Use of pretreated ingredients
    • C08K9/12—Adsorbed ingredients, e.g. ingredients on carriers

Abstract

The invention discloses a sandwich-shaped chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide for food packaging, and a preparation method and application thereof. The method comprises the following steps: taking corn straws as a reducing agent and graphene oxide as a template to obtain a reduced graphene oxide fixed nano-silver composite solution; the antibacterial composite membrane for packaging the sandwich-like chitosan-based food is prepared by self-assembling layers by layers through the electrostatic action between the reduced graphene oxide and the chitosan. The chitosan-based composite membrane obtained by the invention fixes nano-silver under the dual actions of reducing graphene oxide and a sandwich structure, and achieves the effect of lasting slow release. The accumulative release experiment shows that the release rate of the nano-silver of the composite film after 14 days is only 0.5-6 wt%. When the composite film is applied to food packaging, the nano silver particles with the antibacterial effect can not be released into food too fast, so that the problem of accumulated toxicity in the food packaging application is avoided.

Description

Sandwich-shaped chitosan-based antibacterial composite film with nano-silver fixed by reduced graphene oxide for food packaging and preparation method and application thereof
Technical Field
The invention relates to the field of food packaging materials, in particular to a sandwich-shaped chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide for food packaging and a preparation method and application thereof.
Background
Microbial contamination can cause deterioration of food quality and shorten the shelf life of food, and the packaging material special for food plays an important role in the protection and preservation of food. In recent years, people are continuously working on finding an antibacterial food packaging material with strong barrier property and environmental friendliness to meet the requirement of modern food active packaging, so that the food packaging material is beneficial to prolonging the storage period of food, improving the storage environment of food and reducing the pollution to the environment. The chitosan is a natural polysaccharide which has the advantages of no toxicity, good biocompatibility, rich resources, excellent film forming and oxygen resistance, and has great application value in the field of food packaging materials. Its weak mechanical strength and low antibacterial ability limit its application in the field of food packaging.
The silver nanoparticles have broad-spectrum antibacterial capability, so that the silver nanoparticles are concerned in the field of food antibacterial packaging materials, and the nano silver-based packaging materials are applied to the field of inhibiting food-borne bacteria. However, the conventional nano silver is easily aggregated into clusters due to its high surface energy, which impairs its antibacterial activity. In addition, excessive nano silver release has certain accumulated toxicity harm to human bodies. When the nano silver is added into a packaging film as an antibacterial agent, if the nano silver is not fixed properly, the nano silver can be released from a packaging material too quickly, and finally, the problem of accumulated toxicity of cells is caused, so that the nano silver causes damage to a human body and limits the development of the nano silver in the food packaging industry. To solve these problems, it is necessary to sufficiently disperse and fix the nano silver. Dung et al prepared nanocomposite films between Silver nanoparticles (Ag NPs) and Low Density Polyethylene (LDPE) using masterbatch by melt extrusion and melt compounding (Deng J, Quan M, Ding, et al preparation of Nano-Silver-continuous Polyethylene Composite Film and Ag Ion grafting in Food-simulans. journal of biological Nanotechnology 2020,3, 1613-1621.). The composite membrane has a larger bacteriostatic zone, but the too fast release of the nano-silver can cause the problem of cytotoxicity.
The graphene oxide has the advantages of no toxicity, good film-forming property, high mechanical strength, good biocompatibility and large specific surface area, and can be used as a carrier of nano silver to promote uniform dispersion and fixation of the nano silver and prevent agglomeration. However, the bonding strength of graphene oxide and nano silver is not sufficient, and too fast release of nano silver may also be caused.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a sandwich-shaped chitosan-based antibacterial composite film for fixing nano-silver by reduced graphene oxide for food packaging, and a preparation method and application thereof.
The invention aims to provide a multifunctional composite film for food packaging, in particular to a sandwich-shaped chitosan-based composite film which is nontoxic and has a lasting antibacterial effect and is formed by fixing nano-silver by reduced graphene oxide.
The invention also aims to provide a preparation method of the sandwich-shaped chitosan-based antibacterial composite membrane for fixing nano-silver by using the reduced graphene oxide for food packaging. According to the preparation method, corn straws are used as a green reducing agent to prepare nano silver, graphene oxide is used as a template to load and fix the nano silver, and a reduced graphene oxide/nano silver composite solution is obtained; then, the antibacterial composite membrane for packaging the chitosan-based food is formed by self-assembling layers by layers through the electrostatic action of the reduced graphene oxide and the chitosan, so that the effects of slowly releasing the nano-silver and lasting antibacterial are achieved.
The purpose of the invention is realized by at least one of the following technical solutions.
According to the invention, a sandwich-like structure is formed by layer-by-layer self-assembly by utilizing the electrostatic interaction between graphene oxide and chitosan, and the structure is further fixed to slow down the release of nano-silver.
The invention provides a preparation method of a sandwich-shaped chitosan-based antibacterial composite membrane with reduced graphene oxide fixed nano-silver for food packaging.
The invention provides a preparation method of a sandwich-shaped chitosan-based antibacterial composite membrane for fixing nano-silver by reduced graphene oxide for food packaging, which comprises the following steps:
(1) removing impurities from the collected corn straws, washing, drying, crushing by a crusher (forming powder under the action of mechanical external force of the crusher), performing ball milling treatment by a ball mill to obtain corn straw powder, and dissolving the corn straw powder in a sodium hydroxide/urea system by adopting a low-temperature freeze thawing method to obtain a corn straw solution;
(2) adding the silver-ammonia solution into the graphene oxide solution under the stirring condition, and uniformly mixing to obtain a graphene oxide/silver-ammonia mixed solution;
(3) adding the corn stalk solution obtained in the step (1) into the graphene oxide/silver ammonia mixed solution obtained in the step (2) to obtain a reaction solution, and performing a reduction reaction under the microwave-assisted condition (the graphene oxide is partially reduced while the nano-silver is obtained by reduction preparation), so as to obtain a reduced graphene oxide/nano-silver solution;
(4) dripping glycerin into the chitosan solution under the condition of stirring to obtain glycerin/chitosan mixed solution; and (3) carrying out layer-by-layer self-assembly on the reduced graphene oxide/nano-silver solution in the step (3) and the mixed solution through electrostatic interaction to obtain the sandwich-shaped chitosan-based antibacterial composite film (the sandwich-shaped composite film of the reduced graphene oxide nano-silver coated by chitosan) for fixing the nano-silver by the reduced graphene oxide for food packaging.
Further, the grain diameter of the corn straw powder in the step (1) is 40-60 meshes; the ball milling time is 8-10 h.
Further, the sodium hydroxide/urea system in the step (1) is a mixed solution obtained by uniformly mixing sodium hydroxide, urea and water; in the sodium hydroxide/urea system, the mass fraction of sodium hydroxide is 2-7%, and the mass fraction of urea is 8-15%; in the corn stalk solution in the step (1), the concentration of the corn stalk powder is 0.1-5 g/L.
Further, the concentration of the silver ammonia solution in the step (2) is 0.01-1 mol/L; the concentration of the graphene oxide solution is 0.5-2 g/L; the volume ratio of the silver ammonia solution to the graphene oxide solution is 1:2-1: 40.
Preferably, the volume ratio of the silver ammonia solution to the graphene oxide solution in the step (2) is 1:2-1: 20.
further, the volume of the corn stalk solution in the step (3) is 30-70% of the volume of the reaction solution; the temperature of the reduction reaction is 30-90 ℃, the time of the reduction reaction is 10-80min, and the power of the microwave is 300-900W.
Further, in the chitosan solution in the step (4), the mass fraction of the chitosan is 0.2-4%; the mass of the glycerol is 5-20% of that of the chitosan solution.
Further, the volume ratio of the reduced graphene oxide/nano silver solution to the chitosan solution in the step (4) is 1:10-1: 2; the layer-by-layer self-assembly comprises: pouring a layer of glycerin/chitosan mixed solution into a container (preferably a polytetrafluoroethylene container), performing primary drying treatment (drying to a semi-dry state), pouring a layer of reduced graphene oxide/nano-silver solution into the container, performing secondary drying treatment (drying to a semi-dry state), pouring a layer of glycerin/chitosan mixed solution into the container, and performing tertiary drying treatment (complete drying) to obtain the sandwich-shaped chitosan-based antibacterial composite membrane for fixing nano-silver by reduced graphene oxide for food packaging.
Further, the time of the first drying treatment in the step (4) is 2-6 h; the time of the second drying treatment is 2-6 h; the time of the third drying treatment is 6-12 h; the temperature of the first drying treatment, the second drying treatment and the third drying treatment is 30-60 ℃.
The invention provides a sandwich-shaped chitosan-based antibacterial composite film prepared by the preparation method, wherein the nano-silver is fixed by reduced graphene oxide for food packaging, and the cumulative release rate of the nano-silver is 0.5-6 wt% after 14 days.
The invention provides application of a sandwich-shaped chitosan-based antibacterial composite film with nano-silver fixed by reduced graphene oxide for food packaging in food packaging. The composite film has good oxygen resistance, mechanical property and antibacterial activity, and can meet the requirements of modern food antibacterial packaging materials.
Compared with the prior art, the invention has the following advantages and beneficial effects:
(1) according to the preparation method provided by the invention, the agricultural wastes, namely corn straws and marine wastes, namely chitosan are wide in source, low in cost, safe, nontoxic and biodegradable;
(2) according to the preparation method provided by the invention, the graphene oxide is used for adsorbing and immobilizing the nano-silver particles, and the nano-silver particles and the chitosan solution are self-assembled layer by layer through electrostatic interaction to form a sandwich-shaped composite film for food packaging and fresh keeping, so that the nano-silver particles with an antibacterial effect cannot be released into food too fast to cause accumulated toxicity, the harm of the nano-silver particles in food application is avoided, and the application of the nano-silver particles as an antibacterial agent in food fresh keeping is expanded;
(3) the preparation method provided by the invention is simple and easy to operate, has low energy consumption, and is beneficial to large-scale industrial production;
(4) the 14-day release rate of the nano-silver in the sandwich-shaped chitosan-based antibacterial composite film (the sandwich-shaped chitosan-based antibacterial composite film with the nano-silver fixed by the reduced graphene oxide) for packaging the food, disclosed by the invention, is only 0.5-6 wt%, and the sandwich-shaped chitosan-based antibacterial composite film has a good antibacterial effect and can be applied to food packaging.
Drawings
Fig. 1 is a graph showing the cumulative release rate of nano-silver within 14 days in the reduced graphene oxide immobilized nano-silver sandwich-like chitosan-based composite membrane obtained in example 3.
Fig. 2 is a graph showing the antibacterial effect of the reduced graphene oxide-immobilized nano-silver sandwich-like chitosan-based composite membrane prepared in example 2 and example 3 on escherichia coli and staphylococcus aureus.
Detailed Description
The following description of the embodiments of the present invention is provided in connection with the accompanying drawings and examples, but the invention is not limited thereto. It is noted that the processes described below, if not specifically described in detail, are all realizable or understandable by those skilled in the art with reference to the prior art. The reagents or apparatus used are not indicated to the manufacturer, and are considered to be conventional products available by commercial purchase.
Example 1
The preparation method of the sandwich-shaped chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide comprises the following steps:
(1) crushing and ball-milling the collected corn straws for 8 hours to prepare powder (the particle size of the powder is 40-60 meshes); freezing and melting 0.01g of corn stalk powder in a 100mL 2 wt% sodium hydroxide/8 wt% urea system (a mixed solution obtained by uniformly mixing sodium hydroxide, urea and water) at a low temperature to obtain a corn stalk solution for later use;
(2) preparing a graphene oxide solution with the concentration of 0.5g/L, adding 20mL of a silver ammonia solution with the concentration of 0.01mol/L into 40mL of the graphene oxide solution under the stirring condition, and uniformly mixing to obtain a graphene oxide-silver ammonia mixed solution;
(3) under the microwave-assisted condition, adding the corn straw solution with the concentration of 0.1g/L obtained in the step (1) into the graphene oxide-silver ammonia mixed solution obtained in the step (2) to obtain a reaction solution, wherein the volume of the corn straw solution is 30% of the volume of the reaction solution, the microwave-assisted reaction time is 10min, the reaction temperature is 30 ℃, and the reaction power is 300W; reducing the nano silver, and simultaneously reducing part of the graphene oxide to obtain a reduced graphene oxide/nano silver composite antibacterial agent;
(4) preparing a chitosan solution with the mass fraction of 0.2%, and adding glycerol (serving as a plasticizer) into the chitosan solution under stirring, wherein the mass fraction of the glycerol relative to the chitosan solution is 5%; pouring a layer of 5mL of chitosan solution into a polytetrafluoroethylene container, and drying at 30 ℃ to be in a semi-dry state (the drying time is 6 h); pouring a layer of 1mL of the reduced graphene oxide nano silver antibacterial agent obtained in the step (3), and drying at the temperature of 30 ℃ to a semi-dry state (the drying time is 5 hours); and finally, laying a layer of 5mL of chitosan solution, drying at 30 ℃ to form a film (the drying time is 12h), and removing the composite film to obtain the sandwich-shaped chitosan-based antibacterial composite film with the nano-silver fixed by the reduced graphene oxide.
Finally, the oxygen transmission rate of the composite membrane is 545cm3/m224h Mpa, 100cm lower than pure chitin membrane oxygen transmission rate3/m224h Mpa, which shows that the composite membrane has good oxygen resistance. The tensile strength of the composite membrane reaches 20MPa, which is 5MPa higher than that of a pure chitin membrane, and the composite membrane has good mechanical properties.
After 14 days, the release rate of the nano silver in the sandwich-like chitosan composite film with the nano silver fixed by the reduced graphene oxide is lower, and is only 0.5 wt%, which indicates that the sandwich structure of the reduced graphene oxide and the film has good immobilization efficiency on the nano silver, and can prevent overflow and leakage of the nano silver.
Example 2
The preparation method of the sandwich-shaped chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide comprises the following steps:
(1) crushing and ball-milling the collected corn straws for 8.5h to prepare powder (the particle size of the powder is 40-60 meshes); freezing and melting 0.1g of corn stalk powder in a 100mL 3 wt% sodium hydroxide/9 wt% urea system (mixed solution obtained by uniformly mixing sodium hydroxide, urea and water) at low temperature to obtain a corn stalk solution for later use;
(2) preparing a graphene oxide solution with the concentration of 0.8g/L, adding 10mL of a silver ammonia solution with the concentration of 0.03mol/L into 40mL of the graphene oxide solution under the stirring condition, and uniformly mixing to obtain a graphene oxide-silver ammonia mixed solution;
(3) under the microwave-assisted condition, adding the corn straw solution with the concentration of 1g/L obtained in the step (1) into the graphene oxide-silver ammonia mixed solution obtained in the step (2) to obtain a reaction solution, wherein the volume of the corn straw solution is 40% of the volume of the reaction solution, the microwave-assisted reaction time is 20min, the reaction temperature is 40 ℃, and the reaction power is 400W; reducing the nano silver, and simultaneously reducing part of the graphene oxide to obtain a reduced graphene oxide nano silver composite antibacterial agent;
(4) preparing a chitosan solution with the mass fraction of 1%, adding 7% of glycerol (as a plasticizer) into the chitosan solution while stirring, pouring a layer of 5mL of chitosan solution into a polytetrafluoroethylene container, and drying the chitosan solution to a semi-dry state at the temperature of 35 ℃ (the drying time is 5 h); pouring a layer of 2mL of the reduced graphene oxide nano silver antibacterial agent obtained in the step (3), and drying at 35 ℃ to a semi-dry state (the drying time is 6 hours); finally, a layer of 5mL chitosan solution is paved, and the film is dried at the temperature of 35 ℃ for 10 h. And (4) removing the composite membrane to obtain the sandwich-shaped chitosan-based antibacterial composite membrane with the nano-silver fixed by the reduced graphene oxide. The sandwich-like chitosan-based antibacterial composite membrane prepared in example 2 and with nano-silver immobilized by reduced graphene oxide is labeled as CS/rGO @ AgNPs-3.
Finally, the oxygen transmission rate of the composite membrane is measured to be 525cm3/m224h Mpa, 120cm lower than pure chitin membrane oxygen transmission rate3/m224h Mpa, which shows that the composite membrane has good oxygen resistance. The tensile strength of the composite film reaches 25MPa, which is 10MPa higher than that of pure chitin film, thus the composite film has good mechanical propertyCan be used.
After 14 days, the release rate of the nano silver in the sandwich-like chitosan composite film with the nano silver fixed by the reduced graphene oxide is lower, and is only 1 wt%, which indicates that the sandwich structure of the reduced graphene oxide and the film has good immobilization efficiency on the nano silver, and can prevent overflow and leakage of the nano silver.
An experimental graph of the prepared sandwich-shaped chitosan-based composite membrane with the nano-silver fixed by the reduced graphene oxide on the antibiosis of staphylococcus aureus and escherichia coli. In FIG. 2, CS represents a pure chitosan film, CS/rGO represents a reduced graphene oxide chitosan film (the preparation of the reduced graphene oxide chitosan film is similar to that of CS/rGO @ AgNPs-3, except that a silver ammonia solution and a corn straw solution are not added, and the rest steps are the same as those of the embodiment 2), CS/rGO @ AgNPs-3 represents a composite film obtained in the embodiment 2, and CS/rGO @ AgNPs-4 represents a composite film obtained in the embodiment 3; as shown in fig. 2. As can be seen from the sample No. 3 (CS/rGO @ AgNPs-3) in FIG. 2, the prepared sandwich-shaped chitosan composite membrane with the nano-silver fixed by the reduced graphene oxide has good antibacterial effects on escherichia coli and staphylococcus aureus, and the diameters of the inhibition zones are 2.1cm and 3.2cm respectively.
Example 3
The preparation method of the sandwich-shaped chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide comprises the following steps:
(1) crushing and ball-milling the collected corn straws for 8.5h to prepare powder (the particle size of the powder is 40-60 meshes); freezing and melting 0.2g of corn stalk powder in a 100mL 4 wt% sodium hydroxide/11 wt% urea system (mixed solution obtained by uniformly mixing sodium hydroxide, urea and water) at low temperature to obtain a corn stalk solution for later use;
(2) preparing a graphene oxide solution with the concentration of 1g/L, adding 8mL of a silver ammonia solution with the concentration of 0.5mol/L into 40mL of the graphene oxide solution under the stirring condition, and uniformly mixing to obtain a graphene oxide-silver ammonia mixed solution;
(3) under the microwave-assisted condition, adding the corn straw solution with the concentration of 2g/L obtained in the step (1) into the graphene oxide-silver ammonia mixed solution obtained in the step (2) to obtain a reaction solution, wherein the volume of the corn straw solution is 50% of the volume of the reaction solution, the microwave-assisted reaction time is 40min, the reaction temperature is 50 ℃, and the reaction power is 600W; reducing the nano silver, and simultaneously reducing part of the graphene oxide to obtain a reduced graphene oxide nano silver composite antibacterial agent;
(4) preparing a chitosan solution with the mass fraction of 2%, and adding 10% of glycerol (serving as a plasticizer) into the chitosan solution under stirring, wherein the mass fraction of the glycerol relative to the chitosan solution is 10%; pouring a layer of 5mL of chitosan solution into a polytetrafluoroethylene container, and drying at 40 ℃ to be in a semi-dry state (the drying time is 4 h); pouring a layer of 3mL of the reduced graphene oxide nano silver antibacterial agent obtained in the step (3), and drying at 40 ℃ to be in a semi-dry state (the drying time is 4 hours); finally, a layer of 5mL chitosan solution is paved, and the film is dried at the temperature of 40 ℃ for forming (the drying time is 8 h). And (4) removing the composite membrane to obtain the sandwich-shaped chitosan-based antibacterial composite membrane with the nano-silver fixed by the reduced graphene oxide.
Finally measuring the oxygen transmission rate of the composite membrane to be 505cm3/m224h Mpa, 140cm lower than pure chitin membrane oxygen transmission rate3/m224h Mpa, which shows that the composite membrane has good oxygen resistance. The tensile strength of the composite membrane reaches 27MPa, which is 12MPa higher than that of a pure chitin membrane, and the composite membrane has good mechanical properties.
The result of the cumulative release rate of the nano-silver in the prepared sandwich-like chitosan composite membrane with the nano-silver fixed by the reduced graphene oxide is shown in fig. 1. As can be seen from fig. 1, after 14 days, the release rate of nano silver in the sandwich-like chitosan composite film in which nano silver is immobilized by reduced graphene oxide is low, which is only 1.9%, which indicates that the sandwich structure of reduced graphene oxide and the film has good immobilization efficiency for nano silver, and can prevent overflow and leakage of nano silver.
An experimental chart of the prepared sandwich-shaped chitosan composite membrane with the nano-silver fixed by the reduced graphene oxide on the antibiosis of staphylococcus aureus and escherichia coli is shown in fig. 2. As can be seen from the sample No. 4 (CS/rGO @ AgNPs-4) in FIG. 2, the prepared sandwich-shaped chitosan composite membrane with the nano-silver fixed by the reduced graphene oxide has good antibacterial effects on escherichia coli and staphylococcus aureus, and the diameters of the antibacterial zones are 2.8cm and 3.9cm respectively. In addition, the concentration of the silver ammonia solution is increased, so that the diameter of the inhibition zone is increased.
Example 4
The preparation method of the sandwich-shaped chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide comprises the following steps:
(1) crushing and ball-milling the collected corn straws for 9 hours to prepare powder (the particle size of the powder is 40-60 meshes); freezing and melting 0.3g of corn stalk powder in 100ml of 6 wt% sodium hydroxide/13 wt% urea system (mixed solution obtained by uniformly mixing sodium hydroxide, urea and water) at low temperature to obtain corn stalk solution for later use;
(2) preparing a graphene oxide solution with the concentration of 1.5g/L, adding 4mL of a silver ammonia solution with the concentration of 0.8mol/L into 40mL of the graphene oxide solution under the stirring condition, and uniformly mixing to obtain a graphene oxide-silver ammonia mixed solution;
(3) under the microwave-assisted condition, adding the corn straw solution with the concentration of 3g/L obtained in the step (1) into the graphene oxide-silver ammonia mixed solution obtained in the step (2) to obtain a reaction solution, wherein the volume of the corn straw solution is 60% of the volume of the reaction solution, the microwave-assisted reaction time is 60min, the reaction temperature is 70 ℃, and the reaction power is 700W; reducing the nano silver, and simultaneously reducing part of the graphene oxide to obtain a reduced graphene oxide nano silver composite antibacterial agent;
(4) preparing a chitosan solution with the mass fraction of 3%, and adding glycerol (serving as a plasticizer) into the chitosan solution under stirring, wherein the mass fraction of the glycerol relative to the chitosan solution is 15%; pouring a layer of 5mL of chitosan solution into a polytetrafluoroethylene container, and drying at 50 ℃ to be in a semi-dry state (the drying time is 3 h); pouring a layer of 4mL of the reduced graphene oxide nano silver antibacterial agent obtained in the step (3), and drying at 50 ℃ to a semi-dry state (the drying time is 3 hours); finally, a layer of 5mL chitosan solution is paved, and the mixture is dried at the temperature of 50 ℃ to form a film (the drying time is 6 h); and (4) removing the composite membrane to obtain the sandwich-shaped chitosan-based antibacterial composite membrane with the nano-silver fixed by the reduced graphene oxide.
Finally, the oxygen transmission rate of the composite membrane is 495cm3/m224h Mpa, 150cm lower than pure chitin membrane oxygen transmission rate3/m224h Mpa, which shows that the composite membrane has good oxygen resistance. The tensile strength of the composite membrane reaches 29MPa, which is 14MPa higher than that of a pure chitin membrane, and the composite membrane has good mechanical properties. After 14 days, the release rate of the nano silver in the sandwich-like chitosan composite film with the nano silver fixed by the reduced graphene oxide is lower, and is only 2.1 wt%, which indicates that the sandwich structure of the reduced graphene oxide and the film has good immobilization efficiency on the nano silver, and can prevent overflow and leakage of the nano silver.
Example 5
The preparation method of the sandwich-shaped chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide comprises the following steps:
(1) crushing and ball-milling the collected corn straws for 10 hours to prepare powder (the particle size of the powder is 40-60 meshes); freezing and melting 0.5g of corn stalk powder in 100ml of a 7 wt% sodium hydroxide/15 wt% urea system (a mixed solution obtained by uniformly mixing sodium hydroxide, urea and water) at a low temperature to obtain a corn stalk solution for later use;
(2) preparing a graphene oxide solution with the concentration of 2g/L, adding 2mL of a silver ammonia solution with the concentration of 1mol/L into 40mL of the graphene oxide solution under the stirring condition, and uniformly mixing to obtain a graphene oxide-silver ammonia mixed solution;
(3) under the microwave-assisted condition, adding the corn straw solution with the concentration of 5g/L obtained in the step (1) into the graphene oxide-silver ammonia mixed solution obtained in the step (2) to obtain a reaction solution, wherein the volume of the corn straw solution is 70% of the volume of the reaction solution, the microwave-assisted reaction time is 80min, the reaction temperature is 90 ℃, and the reaction power is 800W; reducing the nano silver, and simultaneously reducing part of the graphene oxide to obtain the reduced graphene oxide nano silver composite antibacterial agent; agent for treating cancer
(4) Preparing a chitosan solution with the mass fraction of 4%, and adding glycerol (serving as a plasticizer) into the chitosan solution under stirring, wherein the mass fraction of the glycerol relative to the chitosan solution is 20%; pouring a layer of 5mL of chitosan solution into a polytetrafluoroethylene container, and drying at 60 ℃ to be in a semi-dry state (the drying time is 2 h); pouring a layer of 5mL of the reduced graphene oxide nano silver antibacterial agent obtained in the step (3), and drying at the temperature of 60 ℃ to a semi-dry state (the drying time is 2 hours); finally, a layer of 5mL chitosan solution is paved, and the mixture is dried at the temperature of 60 ℃ to form a film (the drying time is 12 h); and (4) removing the composite membrane to obtain the sandwich-shaped chitosan-based antibacterial composite membrane with the nano-silver fixed by the reduced graphene oxide.
Finally measuring the oxygen transmission rate of the composite membrane to be 475cm3/m224h Mpa, 170cm lower than pure chitin membrane3/m224h Mpa, which shows that the composite membrane has good oxygen resistance. The tensile strength of the composite membrane reaches 30MPa, which is 15MPa higher than that of a pure chitin membrane, and the composite membrane has good mechanical properties.
After 14 days, the release rate of the nano silver in the sandwich-like chitosan composite film with the nano silver fixed by the reduced graphene oxide is lower, and is only 6 wt%, which indicates that the sandwich structure of the reduced graphene oxide and the film has good immobilization efficiency on the nano silver, and can prevent overflow and leakage of the nano silver.
The above examples are only preferred embodiments of the present invention, which are intended to be illustrative and not limiting, and those skilled in the art should understand that they can make various changes, substitutions and alterations without departing from the spirit and scope of the invention.

Claims (10)

1. A preparation method of a sandwich-shaped chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide for food packaging is characterized by comprising the following steps:
(1) washing, drying, crushing and ball-milling corn straws to obtain corn straw powder, and dissolving the corn straw powder in a sodium hydroxide/urea system by adopting a low-temperature freeze-thaw method to obtain a corn straw solution;
(2) adding the silver-ammonia solution into the graphene oxide solution under the stirring condition, and uniformly mixing to obtain a graphene oxide/silver-ammonia mixed solution;
(3) adding the corn straw solution obtained in the step (1) into the graphene oxide/silver ammonia mixed solution obtained in the step (2) to obtain a reaction solution, and carrying out reduction reaction under the microwave-assisted condition to obtain a reduced graphene oxide/nano silver solution;
(4) dripping glycerin into the chitosan solution under the condition of stirring to obtain glycerin/chitosan mixed solution; and (3) carrying out layer-by-layer self-assembly on the reduced graphene oxide/nano-silver solution in the step (3) and the glycerin/chitosan mixed solution through electrostatic interaction to obtain the sandwich-shaped chitosan-based antibacterial composite film with the reduced graphene oxide fixed nano-silver for food packaging.
2. The preparation method of the sandwich-like chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide for food packaging according to claim 1, wherein the particle size of the corn stalk powder in step (1) is 40-60 mesh; the ball milling time is 8-10 h.
3. The preparation method of the sandwich-like chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide for food packaging according to claim 1, wherein the sodium hydroxide/urea system in step (1) is a mixed solution obtained by uniformly mixing sodium hydroxide, urea and water; in the sodium hydroxide/urea system, the mass fraction of sodium hydroxide is 2-7%, and the mass fraction of urea is 8-15%; in the corn stalk solution in the step (1), the concentration of the corn stalk powder is 0.1-5 g/L.
4. The preparation method of the sandwich-like chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide for food packaging according to claim 1, wherein the concentration of the silver ammonia solution in the step (2) is 0.01-1 mol/L; the concentration of the graphene oxide solution is 0.5-2 g/L; the volume ratio of the silver ammonia solution to the graphene oxide solution is 1:2-1: 20.
5. The preparation method of the sandwich-like chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide for food packaging according to claim 1, wherein the volume of the corn stalk solution in the step (3) is 30-70% of the volume of the reaction solution; the temperature of the reduction reaction is 30-90 ℃, the time of the reduction reaction is 10-80min, and the power of the microwave is 300-900W.
6. The preparation method of the sandwich-like chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide for food packaging according to claim 1, wherein in the chitosan solution in the step (4), the mass fraction of chitosan is 0.2-4%; the mass of the glycerol is 5-20% of that of the chitosan solution.
7. The preparation method of the sandwich-like chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide for food packaging according to claim 1, wherein the volume ratio of the reduced graphene oxide/nano-silver solution to the chitosan solution in the step (4) is 1:10-1: 2; the layer-by-layer self-assembly comprises: pouring a layer of glycerin/chitosan mixed solution into a container, performing primary drying treatment, pouring a layer of reduced graphene oxide/nano-silver solution into the container, performing secondary drying treatment, pouring a layer of glycerin/chitosan mixed solution into the container, and performing tertiary drying treatment to obtain the sandwich-shaped chitosan-based antibacterial composite film for fixing nano-silver by reduced graphene oxide for food packaging.
8. The preparation method of the sandwich-like chitosan-based antibacterial composite membrane with nano-silver fixed by reduced graphene oxide for food packaging according to claim 7, wherein the time of the first drying treatment in step (4) is 2h to 6 h; the time of the second drying treatment is 2-6 h; the time of the third drying treatment is 6-12 h; the temperature of the first drying treatment, the second drying treatment and the third drying treatment is 30-60 ℃.
9. The sandwich-like chitosan-based antibacterial composite film prepared by the preparation method of any one of claims 1 to 8, in which nano-silver is immobilized by reduced graphene oxide, and the cumulative release rate of nano-silver is 0.5 to 6 wt% after 14 days.
10. The sandwich-like chitosan-based antibacterial composite membrane with nano-silver immobilized by reduced graphene oxide for food packaging according to claim 9, for use in food packaging.
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