WO2024012609A2

WO2024012609A2 - Preparation method for silver-loaded tempo oxidized nanocellulose/chitosan antibacterial preservative film for fruit and vegetable packaging, and use thereof

Info

Publication number: WO2024012609A2
Application number: PCT/CN2023/120961
Authority: WO
Inventors: 杨桂花; 蒋启蒙; 陈嘉川; 王宝斌; 张子俊
Original assignee: 齐鲁工业大学(山东省科学院)
Priority date: 2023-01-04
Filing date: 2023-09-25
Publication date: 2024-01-18
Also published as: GB202400498D0; CN115926257A; GB2622753A; WO2024012609A3

Abstract

The present invention belongs to the field of functional materials, and relates to a preparation method for a silver-loaded TEMPO oxidized nanocellulose/chitosan antibacterial preservative film for fruit and vegetable packaging, and the use thereof. The preparation method comprises: uniformly dispersing TEMPO oxidized nanocellulose, and adding a silver-ammonia solution thereto, so as to obtain a TEMPO oxidized nanocellulose, which immobilizes nano-silver, under microwave conditions; and dissolving chitosan in glacial acetic acid, adding the silver-loaded oxidized nanocellulose thereto, and using a casting evaporation method to prepare the TEMPO oxidized nanocellulose/chitosan composite film, which immobilizes nano-silver. In the present invention, the TEMPO oxidized nanocellulose is used as a reducing agent, a stabilizing agent and an immobilizing agent, such that no chemical reducing agent or stabilizing agent is added; the reduction efficiency is high, the cost is low, and toxicity is avoided; the microwave-assisted catalysis efficiency is high, and the energy consumption is low; and the immobilization effect of the nano-silver is improved by means of the film-forming property of the chitosan, such that the problem of cumulative toxicity caused by excessively fast release of the nano-silver is ameliorated, and the nano-silver is applied to the field of lasting antibacterial preservation of fruits and vegetables.

Description

Preparation method and application of silver-loaded TEMPO oxidized nanocellulose/chitosan antibacterial cling film for fruit and vegetable packaging

This application is required to be submitted to the China Patent Office on January 4, 2023. The application number is 202310006473.1, and the invention name is "A preparation method and application of silver-loaded TEMPO oxidized nanocellulose/chitosan antibacterial cling film for fruit and vegetable packaging" priority of the Chinese patent application, the entire content of which is incorporated into this application by reference.

Technical field

The invention belongs to the field of functional materials, and specifically relates to a preparation method of a TEMPO oxidized nanocellulose/chitosan durable antibacterial cling film with immobilized nanosilver, which can be used in fruit and vegetable packaging and other related fields.

Background technique

The information in this Background section is disclosed solely for the purpose of increasing understanding of the general background of the invention and is not necessarily considered to be an admission or in any way implying that the information constitutes prior art that is already known to a person of ordinary skill in the art.

With the continuous improvement of people's living standards, the expansion of demand for the quality of fruits and vegetables and the excessive use of non-degradable fossil products have caused the continuous deterioration of the ecological environment. How to develop a degradable green pollution-free antibacterial preservation material system while maintaining the quality of fruits and vegetables is one of the important challenges facing mankind. Film packaging is one of the commonly used technologies to maintain the post-harvest quality of fruits and vegetables and extend their shelf life. It has the advantages of low cost, simple operation, and wide applicability. It is a commonly used fruit and vegetable preservation and storage material. However, traditional membrane materials often have the disadvantages of low porosity and poor performance, and are non-biodegradable, which is not conducive to environmental protection. In addition, traditional membrane materials cannot actively kill bacteria and other microorganisms, and cannot reduce the problem of decay and deterioration. This is reflected in the proliferation of bacteria and other microorganisms during the preservation process, causing a large amount of losses. Therefore, it is necessary to adopt green, efficient and degradable methods to improve the antibacterial activity and preservation effect of fruit and vegetable cling film materials.

Contents of the invention

In order to solve the above problems, the present invention proposes a long-lasting fresh-keeping antibacterial composite film for fruit and vegetable packaging with obvious antibacterial and fresh-keeping effects, excellent mechanical and physical properties, simple operation, green and environmentally friendly, and biodegradable, and its preparation method and application.

In order to achieve the above objects, the present invention adopts the following technical solutions:

A first aspect of the invention provides a method for preparing a TEMPO oxidized nanocellulose/chitosan antibacterial cling film with immobilized nanosilver for fruit and vegetable packaging, which includes the following steps:

Disperse TEMPO oxidized nanocellulose evenly, add silver ammonia solution and mix evenly to obtain a mixed solution;

The mixed solution is reacted under microwave conditions, and after the reaction is completed, the unreacted silver ammonia solution is dialyzed to obtain TEMPO oxidized nanocellulose with immobilized silver nanoparticles;

Chitosan is dissolved in glacial acetic acid solution, the TEMPO oxidized nanocellulose immobilized with nanosilver is added, homogeneously dispersed, and then subjected to ultrasonic treatment. Finally, the ultrasonic-treated mixed liquid is placed in a mold using a cast evaporation method. After drying, the TEMPO oxidized nanocellulose/chitosan antibacterial cling film with immobilized nanosilver for fruit and vegetable packaging is obtained;

Wherein, the volume ratio of the mass of the chitosan to the TEMPO oxidized nanocellulose with immobilized silver nanoparticles is 0.1-0.3g:2mL-10mL.

Nanosilver is a nano-level metallic silver element with broad-spectrum antibacterial properties. It has good inhibitory and killing effects on more than 40 common pathogenic microorganisms such as Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. TEMPO oxidized nanocellulose is a green, renewable and environmentally friendly biomass resource. Its molecular chain contains a large number of reducing functional groups, which can be used to prepare precious metal nanosilver through green and efficient reduction without adding chemical reducing agents. , and can be fixed in situ by relying on the long-chain structure of the fiber itself, and can also be compounded with chitosan, which has good film-forming properties, to form an antibacterial cling film, which has broad application prospects. This preparation method has low energy consumption, is simple to operate, is green and environmentally friendly, has a high yield, has uniform products, does not require high equipment, and can be produced on a large scale.

A second aspect of the present invention provides a TEMPO oxidized nanocellulose/chitosan antibacterial cling film with immobilized nanosilver for fruit and vegetable packaging prepared by the above method.

The third aspect of the present invention provides the application of the above-mentioned TEMPO oxidized nanocellulose/chitosan antibacterial preservation film with immobilized nanosilver for fruit and vegetable packaging in long-lasting antibacterial preservation packaging of fruits and vegetables, wherein the fruit and vegetable Including: one or more of strawberries, lychees, grapes, bananas, cherry tomatoes, lettuce, cabbage and cucumbers.

Beneficial effects of the invention

(1) The present invention uses TEMPO oxidized nanocellulose as reducing agent, stabilizer and immobilization agent, without adding any chemical reducing agent and stabilizer, the preparation method is simple, green, high reduction efficiency, low cost and non-toxic;

(2) The microwave-assisted preparation method of the present invention has high catalytic efficiency, good reduction effect, and low energy consumption;

(3) The present invention further improves the fixation effect of nanoparticles by virtue of the film-forming property of chitosan, achieves secondary fixation, reduces the excessive release of nanosilver, solves the problem of cumulative toxicity, and makes it applicable in the field of long-lasting antibacterial preservation of fruits and vegetables. .

Description of drawings

The description and drawings that constitute a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention.

Figure 1 shows the electron microscopy images of TEMPO-oxidized nanocellulose (a) and nanosilver (b) with immobilized silver nanoparticles;

Figure 2 shows the inhibitory zone effects of different composite membranes on Staphylococcus aureus and Escherichia coli, as well as the scanning electron microscope images comparing before and after killing the two bacteria: (a) is Staphylococcus aureus, (d) is Escherichia coli, (b) is normal Staphylococcus aureus, (c) is Staphylococcus aureus that died after being killed by the composite membrane, (e) is normal E. coli, (f) is E. coli that died after being killed by the composite membrane;

Figure 3 shows the effects of different composite films on cherry tomatoes;

Figure 4 shows the effects of different composite films on strawberry preservation.

Detailed ways

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings commonly understood by one of ordinary skill in the art to which this invention belongs.

The invention provides a preparation of TEMPO oxidized nanocellulose/chitosan antibacterial preservation film with immobilized nanosilver and a method for long-lasting antibacterial preservation of fruits and vegetables. A certain amount of TEMPO oxidized nanocellulose is evenly dispersed, and a certain amount of TEMPO oxidized nanocellulose is added. Silver ammonia solution and stir thoroughly, put the mixed solution into a microwave reactor for reaction, and after the reaction is completed, put it into a dialysis bag to dialyze out the unreacted silver ammonia solution to obtain TEMPO oxidized nanocellulose with immobilized silver nanoparticles; A certain amount of chitosan was dissolved in glacial acetic acid solution, and a certain amount of TEMPO oxidized nanocellulose with immobilized silver nanoparticles prepared above was added, uniformly dispersed using a homogenizer, and then the mixed solution was ultrasonically treated, and finally the tape evaporation method was used will mix The combined solution is placed in a mold, and after drying, a TEMPO oxidized nanocellulose/chitosan antibacterial cling film with immobilized nanosilver for fruit and vegetable packaging is obtained.

In some embodiments, it specifically includes the following steps:

(1) Preparation of TEMPO oxidized nanocellulose with immobilized silver nanoparticles: Add 1 to 5 g of TEMPO oxidized nanocellulose to 100 mL of deionized water, disperse evenly through a homogenizer, and then add 0.025M at a mass ratio of 5:2 ~0.3M silver ammonia solution, use a glass rod to stir evenly, place the mixture in a microwave reactor, react at a power of 600~1000W and a temperature of 40~100°C for 20~60 minutes. After the reaction is completed, dialyze out the unreacted silver ions to obtain TEMPO-oxidized nanocellulose with immobilized silver nanoparticles.

(2) Preparation of TEMPO oxidized nanocellulose/chitosan composite antibacterial cling film with immobilized nanosilver for fruit and vegetable packaging: Dissolve 0.5~1.5g chitosan in 100mL 0.1wt% glacial acetic acid solution, and use homogeneous Stir for 2 minutes until chitosan is completely dissolved, then add 10 mL to 50 mL of the TEMPO oxidized nanocellulose with immobilized silver nanoparticles obtained in step (1), mix evenly with a homogenizer, and use the tape evaporation method after ultrasonic treatment. The solution is placed in a mold, and after drying, a TEMPO oxidized nanocellulose/chitosan composite antibacterial cling film with immobilized silver nanoparticles is obtained.

According to the demand for antibacterial cling film materials for final fruit and vegetable packaging, the antibacterial performance of the composite film (taking the antibacterial effect on Staphylococcus aureus and Escherichia coli as an example) and fresh-keeping performance (taking the fresh-keeping effect on cherry tomatoes and strawberries as an example) of the composite film For example), the initial dosage of TEMPO oxidized nanocellulose, the amount of silver ammonia solution added, and the concentration of chitosan can be adjusted according to different actual conditions.

In some embodiments, the nanocellulose in the TEMPO oxidized nanocellulose is cellulose nanofibrils, prepared by the TEMPO oxidation method, and the carboxyl content is 1.4 to 1.6 mmol/L.

In some embodiments, 1 to 5 g of TEMPO oxidized nanocellulose is added to 100 mL of deionized solution.

In some embodiments, the concentration of the silver ammonia solution is 0.025M ~ 0.3M.

In some embodiments, the mass ratio of the TEMPO oxidized nanocellulose solution to the silver ammonia solution is 5:2-3.

In some embodiments, the TEMPO oxidized nanocellulose is fully and uniformly mixed with the silver ammonia solution under the action of glass rod stirring.

In some embodiments, the TEMPO oxidized nanocellulose and the silver ammonia solution are evenly mixed and reacted in a microwave reactor while stirring.

In some embodiments, the power of the microwave reactor is 600-1000W, and the reaction temperature is 40-100°C for 20-60 minutes.

In some embodiments, the dialysis should ensure complete precipitation of unreacted silver ammonia solution, and the time is 48 to 72 hours.

In some embodiments, 0.5-1.5 g chitosan is dissolved in 100 mL 0.1-0.15 wt% glacial acetic acid solution.

In some embodiments, after the chitosan solution and the TEMPO oxidized nanocellulose solution are mixed, the power of the homogenizer is 500-600W, the homogenization is performed at room temperature, and the homogenization time is 2-3 minutes.

In some embodiments, the ultrasonic treatment power of the homogeneous mixed solution is 1200-1300W, the time is 15-20 minutes, and the temperature is 18-20°C.

In some embodiments, the drying involves placing the mold filled with mixed liquid into an oven for drying at a temperature of 38-40°C and a time of 11-12 hours.

The present invention will be further described in detail below with reference to specific embodiments. It should be pointed out that the specific embodiments are for explanation rather than limitation of the present invention.

In the following examples, the inhibition zone test adopts existing methods in the industry. Please refer to the following papers for details:

1. https://doi.org/10.1016/j.indcrop.2020.112987;

2. https://doi.org/10.1016/j.cej.2021.129815;

3. https://doi.org/10.1016/j.msec.2020.111012.

Example 1:

Add 1g TEMPO oxidized nanocellulose to 100mL deionized water, disperse it evenly through a homogenizer, then add 0.025M silver ammonia solution according to a mass ratio of 5:2, stir evenly using a glass rod, and place the mixed solution in three necks The flask was put into a microwave reactor for reaction at a power of 1000W and a temperature of 100°C for 60 minutes. After the reaction was completed, the unreacted silver ammonia solution was dialyzed for 48 hours to obtain TEMPO oxidized nanocellulose with immobilized silver nanoparticles. Dissolve 0.5g chitosan in 100mL 0.1% glacial acetic acid solution, use a homogenizer to stir for 2 minutes until the chitosan is completely dissolved, after ultrasonic treatment, use the cast evaporation method to place the mixed solution into a mold, and dry it to obtain TEMPO oxidized nanocellulose/chitosan antibacterial cling film with immobilized silver nanoparticles.

The diameter of the inhibition zone produced by the prepared composite film against Staphylococcus aureus is 2.21 mm, and the diameter of the inhibition zone against Escherichia coli is 1.30 mm; the preservation time of fresh cherry tomatoes can be up to 9 days, and the preservation time of fresh strawberries can be up to 9 days. The shelf life can be up to 4 days.

Example 2:

Add 2g TEMPO oxidized nanocellulose to 100mL deionized water, disperse it evenly through a homogenizer, then add 0.05M silver ammonia solution according to a mass ratio of 5:2, stir evenly using a glass rod, and place the mixed solution in three necks The flask was put into a microwave reactor for reaction at a power of 800W and a temperature of 80°C for 40 minutes. After the reaction was completed, the unreacted silver ammonia solution was dialyzed for 48 hours to obtain TEMPO oxidized nanocellulose with immobilized silver nanoparticles. Dissolve 1g of chitosan in 100mL of 0.1% glacial acetic acid solution, use a homogenizer to stir for 2 minutes until the chitosan is completely dissolved, and after ultrasonic treatment, use the cast evaporation method to place the mixed solution in a mold and dry it to obtain TEMPO oxidized nanocellulose/chitosan antibacterial cling film with immobilized silver nanoparticles.

The diameter of the inhibition zone produced by the prepared composite film against Staphylococcus aureus is 2.85mm, and the diameter of the inhibition zone against Escherichia coli is 1.80mm; the preservation time of fresh cherry tomatoes can reach 10 days, and the preservation time of fresh strawberries can be up to 10 days. The shelf life can be up to 4 days.

Example 3:

Add 3g of TEMPO oxidized nanocellulose to 100mL of deionized water, disperse it evenly through a homogenizer, then add 0.1M silver ammonia solution according to a mass ratio of 5:2, stir evenly using a glass rod, and place the mixture in three necks The flask was put into a microwave reactor for reaction at a power of 800W and a temperature of 60°C for 30 minutes. After the reaction was completed, the unreacted silver ammonia solution was dialyzed for 72 hours to obtain TEMPO oxidized nanocellulose with immobilized silver nanoparticles. Dissolve 1.5g chitosan in 100mL 0.1% glacial acetic acid solution, use a homogenizer to stir for 2 minutes until the chitosan is completely dissolved, after ultrasonic treatment, use the cast evaporation method to place the mixed solution into a mold, and dry it A TEMPO oxidized nanocellulose/chitosan antibacterial cling film with immobilized silver nanoparticles was obtained.

The diameter of the inhibition zone produced by the prepared composite film against Staphylococcus aureus is 4.58mm, and the diameter of the inhibition zone against Escherichia coli is 2.50mm; the preservation time of fresh cherry tomatoes can reach 12 days, and the preservation time of fresh strawberries can be up to 12 days. The shelf life can be up to 6 days.

Figure 1 shows the TEMPO-oxidized nanocellulose with immobilized silver nanoparticles (a) and the electron microscopy image of the obtained nanosilver (b). The inset in (a) is the particle size distribution of nanosilver.

It can be seen that the silver nanoparticles are evenly attached to the nanocellulose fibers, and the particle size is relatively uniform.

Figure 2 shows the inhibitory zone effects of different composite membranes on Staphylococcus aureus and Escherichia coli, as well as the electron microscope images comparing the killing of the two bacteria before and after. As can be seen from Figure 2, the composite film has a significant inhibitory effect on two types of bacteria, producing an obvious inhibition zone; and compared with the morphology of the bacteria before killing (rounded, smooth), the bacteria after killing Became shriveled and incomplete.

Figures 3 and 4 show the preservation effect of the composite film on fresh cherry tomatoes and strawberries. It can be seen from Figure 3 and Figure 4 that the composite film has a better preservation effect on cherry tomatoes and strawberries. They basically maintained a complete, fresh and shiny state after 12 days and 6 days respectively, and no mildew or volume shrinkage occurred. Phenomenon.

Example 4:

Add 5g TEMPO oxidized nanocellulose to 100mL deionized water, disperse it evenly through a homogenizer, then add 0.2M silver ammonia solution according to a mass ratio of 5:2, stir evenly using a glass rod, and place the mixed solution in three necks The flask was put into a microwave reactor for reaction at a power of 600W and a temperature of 40°C for 20 minutes. After the reaction was completed, the unreacted silver ammonia solution was dialyzed for 72 hours to obtain TEMPO oxidized nanocellulose with immobilized silver nanoparticles. Dissolve 1.5g chitosan in 100mL 0.1% glacial acetic acid solution, use a homogenizer to stir for 2 minutes until the chitosan is completely dissolved, after ultrasonic treatment, use the cast evaporation method to place the mixed solution into a mold, and dry it A TEMPO oxidized nanocellulose/chitosan antibacterial cling film with immobilized silver nanoparticles was obtained.

The diameter of the inhibition zone produced by the prepared composite film against Staphylococcus aureus is 4.10mm, and the diameter of the inhibition zone against Escherichia coli is 2.10mm; the preservation time of fresh cherry tomatoes can reach 10 days, and the preservation time of fresh strawberries can be up to 10 days. The shelf life can be up to 5 days.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

A method for preparing TEMPO oxidized nanocellulose/chitosan antibacterial cling film with immobilized nanosilver for fruit and vegetable packaging, which is characterized by including the following steps:

Disperse TEMPO oxidized nanocellulose evenly, add silver ammonia solution and mix evenly to obtain a mixed solution;

The mixed solution is reacted under microwave conditions, and after the reaction is completed, the unreacted silver ammonia solution is dialyzed to obtain TEMPO oxidized nanocellulose with immobilized silver nanoparticles;

Chitosan is dissolved in glacial acetic acid solution, the TEMPO oxidized nanocellulose immobilized with nanosilver is added, homogeneously dispersed, and then subjected to ultrasonic treatment. Finally, the ultrasonic-treated mixed liquid is placed in a mold using a cast evaporation method. After drying, the TEMPO oxidized nanocellulose/chitosan antibacterial cling film with immobilized nanosilver for fruit and vegetable packaging is obtained;

The volume ratio of the mass of the chitosan to the TEMPO oxidized nanocellulose with immobilized silver nanoparticles is 0.1 to 0.3 g: 2 mL to 10 mL.
The preparation method according to claim 1, characterized in that the nanocellulose used in the TEMPO oxidation of nanocellulose is cellulose nanofibrils, prepared by the TEMPO oxidation method, and the carboxyl content is 1.4 to 1.6 mmol/L.
The preparation method according to claim 1, characterized in that uniformly dispersing TEMPO oxidized nanocellulose is: adding 1 to 5g TEMPO oxidized nanocellulose to 100 mL of deionized water, and uniformly dispersing it through a homogenizer to obtain TEMPO oxidized nanocellulose solution.
The preparation method according to claim 1, characterized in that the concentration of the silver ammonia solution is 0.025M~0.3M.
The preparation method according to claim 1 or 4, characterized in that the mass ratio of the TEMPO oxidized nanocellulose solution and the silver ammonia solution is 5:2-3.
The preparation method according to claim 1, characterized in that the microwave conditions are: power 600-1000W, reaction temperature 40-100°C for 20-60 minutes.
The preparation method according to claim 1, characterized in that the dialysis time is 48 to 72 hours.
The preparation method according to claim 1, wherein the concentration of the glacial acetic acid solution is 0.1-0.15wt%, and the volume ratio of the mass of the chitosan to the glacial acetic acid solution is 0.5-1.5g: 100mL.
The preparation method according to claim 1, characterized in that the homogenizing power is 500-600W, the stirring is at room temperature, and the stirring time is 2-3 minutes.
The preparation method according to claim 1, characterized in that the power of the ultrasonic treatment is 1200-1300W, the time is 15-20min, and the temperature is 18-20°C.
The preparation method according to claim 1, wherein the drying involves placing the mold containing the mixed liquid into an oven for drying at a temperature of 38-40°C and a time of 11-12 hours.
A TEMPO oxidized nanocellulose/chitosan antibacterial cling film with immobilized nanosilver prepared by the method of any one of claims 1 to 11 for packaging fruits and vegetables.
The application of the TEMPO oxidized nanocellulose/chitosan antibacterial preservation film with immobilized nanosilver for fruit and vegetable packaging according to claim 12 in the long-lasting antibacterial preservation packaging of fruits and vegetables, characterized in that the fruits and vegetables include: strawberries, lychees, One or more of grapes, bananas, cherry tomatoes, lettuce, cabbage and cucumbers.