CN114716710A

CN114716710A - Method for improving physical property and oxidation resistance of chitosan film

Info

Publication number: CN114716710A
Application number: CN202210281695.XA
Authority: CN
Inventors: 余达威; 董俊丽; 赵嘉钰; 夏文水; 余紫娟; 姜启兴; 许艳顺
Original assignee: Jiangnan University
Current assignee: Jiangnan University
Priority date: 2022-03-21
Filing date: 2022-03-21
Publication date: 2022-07-08

Abstract

The invention discloses a method for improving the physical property and the oxidation resistance of a chitosan membrane, which comprises the steps of dissolving food-grade chitosan and glycerol in glacial acetic acid to prepare a chitosan membrane preparation solution, and preparing and forming by a solution casting method to prepare a primary chitosan membrane; and (3) treating the primary chitosan membrane for 12-48 h at the high temperature of 80-150 ℃ to obtain the chitosan membrane. The preparation method of the chitosan membrane has simple process, safe and environment-friendly membrane material, excellent performances of the membrane in the aspects of water resistance, tensile strength, light barrier property and the like, and effectively improves the performance defect of the conventional pure chitosan membrane that the environmental applicability is poor.

Description

Method for improving physical property and oxidation resistance of chitosan film

Technical Field

The invention belongs to the field of degradable membrane materials, and particularly relates to a method for improving physical property and oxidation resistance of a chitosan membrane.

Background

The traditional plastic food packaging material has single function and is not easy to degrade, and has great trouble on resource destruction and environmental pollution. With the general goal of the country in proposing the "double carbon" program, new food packaging materials are gradually receiving attention, and biodegradable natural polymers, such as polysaccharides, proteins, lipids and the like, are proposed to be substitutes for plastic packaging materials.

Chitin is a biological macromolecule second to cellulose in abundance in nature, and chitosan prepared by using chitin as a matrix has the advantages of no toxicity, biodegradability, good biocompatibility, bioactivity, easy film formation and the like, and becomes one of the first-choice materials for developing novel film materials. However, further research finds that the single chitosan film is limited in large-scale production and application due to the defects of strong hydrophilicity, mechanical property, barrier property, biological activity and the like, so how to improve the comprehensive performance of the chitosan film becomes a current research hotspot, and a technical support is provided for expanding the applicability of the chitosan film.

The researchers have proposed that the physical and biochemical properties of the finished film are improved by adopting the compound modification of the film-making base material or the chemical modification of chitosan. For example, a cross-linking method is used to prepare a modified chitosan membrane so as to improve the water resistance, mechanical properties and oxidation resistance of the membrane (Sun Qingjie, et al, a chitosan membrane and a preparation method thereof, Chinese patent of the invention, CN201811610418.9), or exogenous materials (such as nano cellulose, etc.) are compounded to improve the basic properties of the chitosan membrane (Wang hong ling, et al, a preparation and performance research of a chitosan/nano cellulose composite membrane [ J ], Guangdong chemical industry, 2021,48(09):50-51, 54). From the results, the current strategy can obviously improve the comprehensive properties of the chitosan, such as mechanical property, barrier property, biological activity and the like. However, both physical formulation and green chemical modification increase the complexity and production cost of the membrane preparation process in terms of the membrane preparation procedure.

Therefore, the exploration of a more concise, convenient, safe and environment-friendly chitosan membrane preparation process is a continuous pursuit target.

Disclosure of Invention

This section is for the purpose of summarizing some aspects of embodiments of the invention and to briefly introduce some preferred embodiments. In this section, as well as in the abstract and the title of the invention of this application, simplifications or omissions may be made to avoid obscuring the purpose of the section, the abstract and the title, and such simplifications or omissions are not intended to limit the scope of the invention.

The present invention has been made keeping in mind the above and/or other problems occurring in the prior art.

Therefore, the present invention aims at providing a method for improving the physical property and the oxidation resistance of the chitosan film to overcome the defects in the prior art.

In order to solve the technical problems, the invention provides the following technical scheme: a method for improving the physical property and the oxidation resistance of a chitosan film comprises the following steps,

dissolving food-grade chitosan and glycerol in glacial acetic acid to prepare a chitosan film-making solution, and preparing and molding by using a solution casting method to prepare a primary chitosan film;

and (3) treating the primary chitosan membrane for 12-48 h at the high temperature of 80-150 ℃ to obtain the chitosan membrane.

As a preferable scheme of the method for improving the physical property and the oxidation resistance of the chitosan film, the method comprises the following steps: the viscosity average Mw of the chitosan is 50-500 kDa, and the concentration of the chitosan is 0.5-3 percent.

As a preferable scheme of the method for improving the physical property and the oxidation resistance of the chitosan film, the method comprises the following steps: the concentration of glycerol is 0.1-0.5%, and the concentration of acetic acid is 0.5-2%.

As a preferable scheme of the method for improving the physical property and the oxidation resistance of the chitosan film, the method comprises the following steps: the mass ratio of chitosan to glycerol is as follows: g is 8-10: 2-4, the mass-to-volume ratio of chitosan to glacial acetic acid is as follows: l is 8-10: 0.8 to 1.

As a preferable scheme of the method for improving the physical property and the oxidation resistance of the chitosan film, the method comprises the following steps: the pH of the film preparation solution system is 4-5.

As a preferable scheme of the method for improving the physical property and the oxidation resistance of the chitosan film, the method comprises the following steps: and casting and forming the chitosan film, wherein the casting and forming temperature is 25-50 ℃.

The invention further aims to overcome the defects in the prior art and provide a product prepared by the method for improving the physical property and the oxidation resistance of the chitosan film, wherein the film tensile strength of the product is 40-54 MPa, and the water vapor barrier property WVP is 5.74-6.31 (10)^-12·g·m^-1·s^-1·Pa^-1) The oxygen barrier OP is 1.48 to 1.82 (10)^-9·g·m^-1·s^-1) The swelling rate is 30-120%, and the DPPH free radical clearance rate is 55-89%.

The invention also aims to overcome the defects in the prior art and provide the application of the product prepared by the method for improving the physical property and the oxidation resistance of the chitosan film in preparing the food-grade packaging material.

The invention has the beneficial effects that:

(1) compared with the chitosan film prepared by one step of the traditional casting method, the chitosan film prepared by the two steps has higher tensile strength and oxygen and water vapor barrier property, the surface of the film is smoother, the ultraviolet barrier property is strong, the oxidation resistance is improved, and the applicability of the film is obviously improved.

(2) From the aspect of the preparation process, the two-step preparation method does not need to introduce exogenous modified/compound materials, and the prepared chitosan membrane is more environment-friendly and safer, has simple membrane preparation process, easy cost control and strong operability, and is suitable for industrial production.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise. Wherein:

FIG. 1 is an ultraviolet spectrum of chitosan film of comparative example and each example of the present invention.

FIG. 2 is a microstructure diagram of a chitosan film according to comparative example and each example of the present invention.

FIG. 3 is a graph showing the moisture content and swelling property of chitosan films according to the comparative example and examples of the present invention.

FIG. 4 is a graph showing the water contact angle of the chitosan films of the comparative example and each example of the present invention.

FIG. 5 is a DPPH radical scavenging graph of chitosan films of comparative examples and examples of the present invention.

Detailed Description

In order to make the aforementioned objects, features and advantages of the present invention more comprehensible, specific embodiments thereof are described in detail below with reference to examples of the specification.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.

Furthermore, reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. The raw materials of the invention are all common commercial products.

Example 1

A chitosan membrane prepared by a casting molding-high temperature modification two-step method comprises the following steps:

(1) dissolving 10 g of chitosan powder (Mw 200kDa, deacetylation degree 85%; m/v) and 3 g of 0.2% (m/v) glycerol in 1L of 1% (v/v) acetic acid solution, stirring for 4 hours to fully dissolve chitosan, and centrifuging to remove insoluble impurities and bubbles to form a uniform chitosan solution;

(2) pouring the film-forming liquid into a lower-cushion PET plastic plate frame by adopting a casting method, horizontally placing, and draining and forming at 25 ℃;

(3) and (3) treating the formed membrane material for 24 hours at the temperature of 90 ℃.

(4) And (3) placing the film in a constant temperature and humidity chamber for balancing to obtain a chitosan film, and obtaining 20 sheets of film material.

Example 2

(3) and (3) treating the formed membrane material for 24 hours in an environment at 100 ℃.

Example 3

(3) and (3) treating the formed membrane material for 24 hours in an environment at 110 ℃.

Example 4

(2) pouring the film-making liquid into a lower-cushion PET plastic plate frame by adopting a casting method, horizontally placing, and draining at 25 ℃ for forming;

(3) and (3) treating the formed membrane material for 24 hours at the temperature of 120 ℃.

Example 5

(3) and (3) treating the formed membrane material for 24 hours in an environment at 130 ℃.

Comparative example 1

A chitosan membrane prepared by a casting and molding one-step method comprises the following steps:

(1) dissolving 10 g of chitosan powder (molecular weight 200kDa, deacetylation degree 85%; m/v) and 3 g of 0.2% (m/v) glycerol in 1L of 1% (v/v) acetic acid solution, stirring for 4 hours to fully dissolve chitosan, and centrifuging to remove insoluble impurities and bubbles to form a uniform chitosan solution;

(3) and (3) placing the film in a constant temperature and humidity box for balancing to obtain a chitosan film, and obtaining 20 sheets of film material.

The chitosan films provided in comparative example 1 and examples 1 to 5 of the present invention were tested for their properties, and the results were as follows:

TABLE 1 appearance and color values of chitosan films of comparative examples and examples

As can be seen from table 1, the chitosan film of the comparative example was in a colorless and transparent state, while the chitosan film of the example was changed in color and transparency. The color change tends to change from dark, red and yellow as the temperature increases from 90 ℃ to 130 ℃, as evidenced by a marked decrease in the values of L and b (darkening and yellowing) and an increase in the values of a (reddening) after a decrease (greenness), as also demonstrated by the results of the total color difference and the browning index. This color change is mainly due to the fact that the temperature promotes the Maillard reaction between carbonyl and amino groups on the chitosan chain, the caramelization reaction caused by the direct heating of the carbohydrate, and the crosslinking reaction in which glycerol participates as a precursor, and the crosslinking rate is affected by the heat treatment temperature. The indication shows that the color change represents the occurrence of crosslinking caused by heat treatment, meaning that each example film has a stronger light-blocking ability than the control film.

The ultraviolet spectrogram of the chitosan film of the comparative example and each example is shown in figure 1.

As can be seen from fig. 1, each set of example chitosan membranes exhibited higher absorbance compared to the control chitosan membrane. The absorbance at 294nm and 420nm indicates a colourless intermediate and a final browned compound (melanin), respectively.

An increase in A294/A420 indicates an intermediate stage of the reaction, while a decrease in A294/A420 indicates a final stage of the reaction, with a temperature of 110 deg.C (example 3) where the ratio is reversed. These results show that the development of browning is very dependent on temperature due to the maillard reaction. Thus, at higher heating temperatures, the formation of colored melanin is faster. The chitosan film prepared by the high-temperature modification two-step method has good light barrier performance, and shows that the chitosan film has potential in the aspect of protecting packaged food from light-related quality loss.

Table 2 comparative examples and examples chitosan film thickness, mechanical tensile and barrier property strength.

As can be seen from Table 2, the average thickness of the film was between 40 and 47 μm. The tensile strength of the chitosan film of the example is higher than that of the chitosan film of the comparative example, which shows that the mechanical property of the film is obviously improved by the heat treatment crosslinking, wherein the tensile strength of the chitosan film of the example 3 is the highest. Water vapor transmission rate and oxygen transmission rate are important barrier performance parameters for food packaging films to prevent the transfer of moisture and oxygen from the surfaces of many food products and their surroundings.

The sum of WVP of the chitosan membrane of the example was significantly reduced compared to the chitosan membrane of the control, achieving good water barrier behavior.

The microstructure of the chitosan film of the comparative example and each example is shown in FIG. 2.

As can be seen from fig. 2, all the films had flat, dense, smooth, uniform surfaces without any signs of fracture. However, compared with the chitosan membrane of the comparative example, the cross-sectional structure of the chitosan membrane prepared by the high-temperature modification two-step method is more compact, which shows that the cross-linking effect exists between chitosan chains induced by the heat treatment. And with the increase of temperature, the cross-linking modification of the microstructure is more easily observed, and the structural difference also influences the physical and chemical properties of the film, such as the improvement of mechanical properties.

The moisture content and swelling property of the chitosan film of the comparative example and each example are shown in FIG. 3.

As can be seen from fig. 3, the chitosan membrane of the comparative example has the highest water content and swelling ratio, which are related to the hydrophilicity of chitosan and glycerol. The moisture content of the chitosan film prepared by the high-temperature modification two-step method is obviously reduced, which is probably caused by the reduction of the binding water sites of the film due to the consumption of amino groups after crosslinking. The swelling value decreases significantly with increasing temperature, which is related to the spatial network compactness of the membrane.

The water contact angle of the chitosan film of the comparative example and each example is shown in FIG. 4.

The water contact angle of each example chitosan membrane tended to decrease significantly compared to the control chitosan membrane, indicating that heating caused the chitosan membrane to increase in hydrophilicity, which was also likely due to the conformation of the molecule and the exposure of the hydrophilic groups on the surface.

DPPH radical scavenging pattern of chitosan membrane in comparative example and each example, FIG. 5.

As can be seen from FIG. 5, the high temperature modification two-step method preparation can improve DPPH-free radical scavenging ability of the chitosan membrane. The chitosan membranes of the examples were higher in DPPH free radical scavenging ability than the chitosan membranes of the control example (47%), with the free radical scavenging ability of the chitosan membrane of example 3 being up to 89%. This shows that the chitosan membrane prepared by the high temperature modification two-step method has the potential of preventing the product from being oxidized.

In conclusion: compared with the chitosan film prepared by the casting and molding one-step method, the chitosan film prepared by the two-step method has better mechanical property, barrier property, waterproofness and oxidation resistance, and the chitosan film has stronger applicability.

The invention adopts the traditional membrane casting molding as the basis, and constructs the chitosan membrane two-step preparation process by introducing the high-temperature modification step. The high-temperature induction enables the film-forming base materials to generate moderate Maillard reaction, and changes the crosslinking degree of the microstructure and the molecular chain in the chitosan single film, thereby improving the water resistance, the tensile strength and the light barrier property of the film. The method does not introduce an exogenous reagent, and the preparation process only adds a high-temperature treatment link, so that the method has the characteristics of greenness, safety and convenience, and the technology can provide a reliable strategy for improving the applicability of the chitosan membrane.

The invention relates to a method for improving the physicochemical property and the biological activity of a finished film by adopting means of compound modification or chemical modification and the like in the prior art. Although the above-mentioned strategy can obviously improve the comprehensive properties of chitosan, such as mechanical property, barrier property and biological activity. But it adds complexity to the process and production cost from the point of view of the membrane preparation procedure; the invention adopts a two-step chitosan film preparation process, utilizes high temperature induction to enable a proper Maillard reaction to occur between film forming base materials, and changes the crosslinking degree of a microstructure and a molecular chain in the chitosan single film, thereby improving the water resistance, the tensile strength and the light barrier property of the film. The preparation process has no introduction of exogenous reagent, and is green, safe and convenient.

The invention provides a preparation method for improving the physical property and the oxidation resistance of a chitosan film, which comprises two key processes of casting forming and high-temperature modification. Firstly, drying a membrane preparation stock solution of a chitosan-glycerol-acetic acid system to prepare a primary membrane by adopting a solution casting method at room temperature, wherein the concentration of chitosan is 0.5-3% (m/v), the concentration of glycerol is 0.1-0.5% (m/v), and the concentration of acetic acid is 0.5-2% (v/v); and treating the primary chitosan film at the high temperature of 80-150 ℃ for 12-48 hours to prepare a finished film. The preparation method of the chitosan membrane has simple process, safe and environment-friendly membrane material, excellent performances of the membrane in the aspects of water resistance, tensile strength, light barrier property and the like, and effectively improves the performance defect of the conventional pure chitosan membrane that the environmental applicability is poor.

It should be noted that the above-mentioned embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.

Claims

1. A method for improving the physical property and the oxidation resistance of a chitosan film is characterized by comprising the following steps: comprises the steps of (a) preparing a mixture of a plurality of raw materials,

2. The method for improving the physical property and the oxidation resistance of the chitosan film as claimed in claim 1, wherein: the viscosity-average Mw of the chitosan is 50-500 kDa, and the concentration of the chitosan is 0.5-3 percent.

3. The method for improving the physical property and the oxidation resistance of the chitosan film according to claim 1 or 2, wherein: the concentration of glycerol is 0.1-0.5%, and the concentration of acetic acid is 0.5-2%.

4. The method for improving the physical property and the oxidation resistance of the chitosan film as claimed in claim 3, wherein: the mass ratio of chitosan to glycerol is as follows: g is 8-10: 2-4, the mass-to-volume ratio of chitosan to glacial acetic acid is as follows: l is 8-10: 0.8 to 1.

5. The method for improving the physical properties and oxidation resistance of chitosan membrane according to any of claims 1, 2, 4, wherein: the pH of the film preparation solution system is 4-5.

6. The method for improving the physical property and the oxidation resistance of the chitosan film as claimed in claim 1, wherein: and casting and forming the chitosan film, wherein the casting and forming temperature is 25-50 ℃.

7. The product obtained by the method for improving the physical property and the oxidation resistance of the chitosan film according to any one of claims 1 to 6.

8. The product of claim 7, wherein: the tensile strength of the film of the product is 40-54 MPa, and the water vapor barrier property WVP is 5.74-6.31 (10)^-12·g·m^-1·s^-1·Pa^-1) The oxygen barrier OP is 1.48 to 1.82 (10)^-9·g·m^-1·s^-1) The swelling ratio is 30-120%.

9. The product of claim 7, wherein: the DPPH free radical clearance rate of the product is 55-89%.

10. Use of a product according to claim 7 for the preparation of a food grade wrapper.