CN114907678A - pH response polylactic acid-based composite membrane and preparation method thereof - Google Patents
pH response polylactic acid-based composite membrane and preparation method thereof Download PDFInfo
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- CN114907678A CN114907678A CN202210485357.8A CN202210485357A CN114907678A CN 114907678 A CN114907678 A CN 114907678A CN 202210485357 A CN202210485357 A CN 202210485357A CN 114907678 A CN114907678 A CN 114907678A
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- 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
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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
- B65D65/466—Bio- or photodegradable packaging materials
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- 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
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- C08J2367/04—Polyesters derived from hydroxy carboxylic acids, e.g. lactones
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- 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
- C08J2405/00—Characterised by the use of polysaccharides or of their derivatives not provided for in groups C08J2401/00 or C08J2403/00
- C08J2405/08—Chitin; Chondroitin sulfate; Hyaluronic acid; Derivatives thereof
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- C—CHEMISTRY; METALLURGY
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- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K5/00—Use of organic ingredients
- C08K5/04—Oxygen-containing compounds
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- 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
- C08K5/00—Use of organic ingredients
- C08K5/04—Oxygen-containing compounds
- C08K5/13—Phenols; Phenolates
- C08K5/132—Phenols containing keto groups, e.g. benzophenones
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W90/00—Enabling technologies or technologies with a potential or indirect contribution to greenhouse gas [GHG] emissions mitigation
- Y02W90/10—Bio-packaging, e.g. packing containers made from renewable resources or bio-plastics
Abstract
The invention belongs to the field of biodegradable materials, and relates to a pH-responsive polylactic acid-based film and a preparation method thereof, wherein the preparation method comprises the following steps: pouring a polylactic acid/chitosan (PLA/CG) film forming solution into a glass surface dish with a weight pressed at the center of a circle to obtain a PLA/CG composite film with a circular hole; and pouring polylactic acid/alizarin (PLA/AL) film forming solution into a circular cavity of the PLA/CG composite film to obtain a PLA/AL composite film filling the circular cavity, and finally peeling the whole film from a glass surface dish to obtain the pH-responsive polylactic acid-based film (PLA/CGA). The pH-responsive polylactic acid-based film obtained by the method has better tensile strength and elongation at break due to the addition of the plasticizer tributyl citrate; meanwhile, the film is endowed with antibacterial performance by adding the chitosan, and the film is endowed with high antioxidant activity and pH responsiveness by adding the alizarin. The pH-responsive polylactic acid-based film obtained by the method can be widely applied as a degradable packaging film or a degradable indicating film.
Description
Technical Field
The invention relates to the field of biodegradable materials, in particular to a pH response polylactic acid-based film and a preparation method thereof.
Background
The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.
With the rapid development of the plastic industry, synthetic polymer materials have replaced traditional materials such as metal, glass, wood and the like in many fields, and are particularly widely applied in the packaging industry. However, due to the serious "white pollution" problem caused by the large use of lunch boxes, packaging bags and disposable trash bags, the development and application of biodegradable materials are attracting more and more attention.
Polylactic acid (PLA) is the most widely studied and utilized biodegradable and renewable thermoplastic polyester with the potential to replace traditional petrochemical-based polymers. The PLA material is completely nontoxic and non-irritant, has better mechanical property than PP, PS and PE, has tensile strength compared with PET, and also has good biocompatibility, biodegradability and processability. PLA can be completely prepared from renewable resources such as corn, potato, sugarcane and the like through a series of synthetic processing, compared with other biodegradable materials and renewable polymer materials, the PLA has the advantages of simpler processing mode and lower cost, and can be industrially produced in factories. Compared with other biopolymers such as Polycaprolactone (PCL), polybutylene succinate (PBS), Polyhydroxyalkanoate (PHA) and the like, the polylactic acid can be used for preparing products through melt extrusion, solution casting, electrostatic spinning and other processing technologies, and is widely applied to food packaging and the like. In recent years, some PLA-based technologies have emerged with an emphasis on achieving equivalent or superior chemical, mechanical and biological properties over traditional polymers. However, as people's awareness of food safety increases, food packaging materials are more expected to have characteristics such as antibacterial property, oxidation resistance, ultraviolet resistance, and intelligent detection of food quality.
Chitosan (CS) is a natural polymer in renewable resources, extracted from shellfish shells and marine product industry waste. Due to its excellent film-forming properties, high transparency, biocompatibility, biodegradability and antibacterial activity, it has attracted extensive attention in the field of food packaging. However, they have problems such as poor mechanical properties, and are generally added as functional components to other polymers that can be used for food packaging to improve the mechanical properties and to sufficiently exert film-forming properties and antibacterial activity.
Recently, an intelligent packaging system is proposed, which can provide real-time quality information of packaged food to consumers through quality indexes such as pH response color-changing films. Alizarin (AL), also known as turkish red, is an alcohol-soluble natural edible colorant extracted from madder roots. In addition to the dye industry, alizarin is a new intelligent choice for monitoring pH changes and improving the physicochemical and functional properties of biopolymer films. The molecular structure of AL changes with pH by linking the hydroxyl group to the carbonyl oxygen atom, allowing proton transfer through intramolecular hydrogen bonding, so that the color changes with acid-base conditions, from yellow at low pH to purple at high pH, with the following structural formula. AL has been used to develop pH response indicator membranes using various polymers such as chitosan, cellulose acetate nanofibers, and the like. Carboxymethyl cellulose (CMC) and Cellulose Nanofibers (CNF) containing AL indicate that the membrane integrity is maintained after three repeated exposures to acid and base gas vapors, and these results indicate that the selection of a suitable support polymer is a necessary factor for the preparation of a reversible pH-responsive membrane.
At present, when the PLA is used for food packaging, modification research mostly adopts a method of adding functional components and singly and purely blending. It is known that Luyanna et al prepare a composite film by a tape casting method using PLA as a base material and Tea Polyphenol (TP) as an antioxidant. Compared with a pure film, the moisture permeability of the film is improved, and when the mass fraction of the tea polyphenol is 1.5%, the composite film has the optimal oxidation resistance. The composite film has good prospect in keeping fruits and vegetables fresh and prolonging the shelf life of food. Zeng Limna, etc. PLA particles, LEO (lemon essential oil) and dichloromethane are mixed, sealed and stirred, and then the mixture is poured into a plate to form a film, and the prepared film is packaged into fresh pork tenderloin to study the antibacterial performance of the pork tenderloin. As a result, growth and reproduction of Escherichia coli and Staphylococcus aureus are inhibited, because the LEO contains terpenes and phenols of aldol, which can effectively inhibit bacterial growth.
Disclosure of Invention
In order to overcome the problems, the invention provides a pH response polylactic acid-based composite membrane and a preparation method thereof, CG (CS grafted with glycine (Gly)), AL and tributyl citrate (TBC) are blended in PLA, so that the production cost of the PLA can be reduced, the toughness is improved, the performances of antibiosis, antioxidation, pH response and the like are endowed, and the application of the PLA is further expanded.
In order to achieve the technical purpose, the technical scheme adopted by the invention is as follows:
in a first aspect of the present invention, there is provided a method for preparing a pH-responsive polylactic acid-based composite membrane, comprising:
dissolving polylactic acid (PLA) in dichloromethane, uniformly dispersing and melting to obtain molten polylactic acid (PLA);
adding glycine-modified chitosan CG into the molten polylactic acid PLA, uniformly mixing, and adding tributyl citrate TBC to obtain a first film-forming solution;
pouring the first film forming solution into a vessel with a column pressed at the center of a circle, and after overnight film forming at room temperature, stripping the column to obtain a dry film with round holes, namely a PLA/CG composite film;
taking another part of the molten polylactic acid PLA, adding alizarin AL, uniformly mixing, adding tributyl citrate TBC, and uniformly mixing to obtain a second film forming solution;
and finally, pouring the second film forming solution into a circular cavity of the PLA/CG composite film, forming a film overnight at room temperature to obtain a PLA/AL composite film, and stripping the PLA/AL composite film from a vessel to obtain the PLA/AL composite film.
In a second aspect of the present invention, there is provided a pH-responsive polylactic acid-based composite membrane prepared by the above-described method.
The invention relates to a method for preparing a pH-responsive polylactic acid-based film by adding two functional substances of modified chitosan and alizarin into molten polylactic acid.
The invention has the beneficial effects that:
(1) the invention successfully prepares the pH-responsive polylactic acid-based film by adding the modified chitosan, the alizarin and the tributyl citrate into the polylactic acid through melt blending. The production cost of PLA is reduced, and the toughness is improved, and meanwhile, the application of PLA is further expanded by adding functional components. CG, AL and TBC are dispersed uniformly in the PLA matrix, and have strong binding force with the PLA matrix, and can obtain expected thermal stability, oxidation resistance, ultraviolet resistance, pH responsiveness, mechanical property and the like.
(2) The functional ingredient AL is added into PLA successfully, and besides pH sensitivity, the AL also shows various functional characteristics, such as color change reversibility, antioxidant activity and ultraviolet ray blocking performance.
(3) In order to prepare the functional PLA-based degradable packaging film, the invention provides that molten PLA, CG and AL are blended, plasticizer TBC is added, and a PLA/CGA film with functional zones (a bacteria inhibiting zone and a pH response zone) is prepared by using a rotary evaporator and a solvent casting method, so that a mechanical forming method with higher requirements on equipment is avoided, and the addition of chemical additives is reduced. However, the experimental results show that: the PLA/CGA film obtained by using 1, 4-dioxane as a solvent cannot achieve the expected effect in the aspects of film integrity and the like and cannot meet the mechanical requirements. For this reason, the present invention uses methylene chloride as a solvent and produces a PLA-based film using a rotary evaporator and a solvent casting method, and found that: the appearance and mechanical properties of the PLA-based film prepared by the solvent casting method are superior to those of the PLA-based film prepared by a rotary evaporator. In the PLA-based blend film prepared by the solvent casting method, CG and AL are uniformly mixed and dispersed in a polymer matrix, and the bonding force with the polymer matrix is strong, so that expected mechanical properties, thermal stability, oxidation resistance, antibiosis, pH response, ultraviolet resistance and the like can be obtained.
(4) The preparation method is simple, convenient to operate and high in practicability.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application.
FIG. 1 is a process scheme for the preparation of pH-responsive polylactic acid-based films according to the present invention.
Fig. 2 shows the antibacterial effect of the polylactic acid film of the PLA and PLA composite film: (a) e.coli; (b) staphylococcus aureus.
FIG. 3 shows the freshness detection results of chicken breast packaged by PLA and PLA/CGA films and stored for 1-10 days.
FIG. 4 is a graph of the color change response of a PLA/CGA film wrapped chicken breast on the first and tenth days.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
A pH response polylactic acid-based film is prepared by taking polylactic acid, glycine modified chitosan and alizarin as raw materials, melting and blending to prepare a film forming solution, and forming a film by a rotary evaporator at room temperature.
In some embodiments, the composite has a tensile strength of 5.7 to 8.1 MPa; the elongation at break is 6.8-30.0%.
In some embodiments, the modified chitosan is 2-10% by mass.
The invention also provides a preparation method of the pH response polylactic acid-based film, which comprises the following steps:
taking polylactic acid, glycine modified chitosan and alizarin as raw materials, taking dichloromethane as a solvent, carrying out melt blending at room temperature to obtain a film forming solution, and forming a film in a glass surface dish by a solvent casting method
The blend of PLA and CS mainly comprises a solution blend method and a melt blend method, and the invention adopts the solution blend method to blend different polymer materials homogeneously, so that the prepared polymer mixture can show the characteristics of different polymer materials in the raw materials, and the defect of a single material is overcome.
In some embodiments, the pH-responsive polylactic acid-based film is formed from methylene chloride as a solvent.
In some embodiments, the alizarin accounts for 0.5-2% by mass.
The invention also provides a preparation method of the excellent pH response polylactic acid based film (PLA/CGA), which comprises the following steps:
preparing a polylactic acid/chitosan (PLA/CG) composite film in a bacteriostasis area:
firstly, weighing 1-2 g of PLA (dried at 50 ℃ for 24 hours before use) and adding the PLA into a beaker containing 20-40 mL of Dichloromethane (DCM), sealing the opening of the beaker, placing the beaker into a constant-temperature ultrasonic reactor, and carrying out ultrasonic treatment for 1.5-3 hours to completely dissolve the PLA; then transferring the molten PLA into a 100ml three-neck flask, adding 2-10 wt% of modified Chitosan (CG), and magnetically stirring for 3-5 hours to uniformly disperse the CG in the PLA solution; then, adding tributyl citrate (TBC) into the solution, and magnetically stirring for 1-2 hours to obtain a film forming solution; and finally, pouring the film forming solution into a glass surface dish with a weight pressed at the circle center, peeling off the weight after overnight film forming at room temperature, and naming the dry film with the round holes as the PLA/CG composite film.
preparation of pH response zone polylactic acid/alizarin (PLA/AL) composite membrane:
firstly, weighing 1-2 g of PLA (dried at 50 ℃ for 24 hours before use) and adding the PLA into a beaker containing 20-40 mL of DCM, sealing the opening of the beaker, placing the beaker into a constant-temperature ultrasonic reactor, and carrying out ultrasonic treatment for 1.5-3 hours to completely dissolve the PLA; then transferring the molten PLA into a 100ml three-neck flask, adding 0.5-2 wt% of Alizarin (AL), and magnetically stirring for 3-5 hours to uniformly disperse the AL in the PLA solution; then adding TBC into the solution, and magnetically stirring for 1-2 hours to obtain a film forming solution; and finally, pouring the film forming solution into a circular hole of the PLA/CG composite film, forming a film overnight at room temperature, and naming the dry film filled in the circular hole as the PLA/AL composite film.
Finally, the entire film was peeled from the glass petri dish to obtain a pH-responsive polylactic acid-based film (PLA/CGA).
Any one of the above-mentioned pH-responsive polylactic acid-based films has a superior effect and meets the international standards of the related industries.
The present invention is described in further detail below with reference to specific examples, which are intended to be illustrative of the invention and not limiting.
In the following examples, the following test methods were employed:
the tensile test is carried out according to the national standard GB/T1024.2-2006, the testing speed is 50mm/min, and the tensile test is carried out at room temperature.
A process for preparing a pH-responsive polylactic acid-based film (see fig. 1), comprising the steps of: preparing a polylactic acid/chitosan (PLA/CG) composite film; preparing a polylactic acid/chitosan/alizarin (PLA/CGA) composite membrane. The PLA/CG film forming solution is poured into a glass surface dish with a weight pressed at the center of a circle, after overnight film forming at room temperature, the weight is peeled off, and a dry film with round holes is named as a PLA/CG composite film; and pouring the PLA/CGA film forming solution into a circular cavity of the PLA/CG composite film, forming a film at room temperature overnight, and peeling the whole film from a glass surface dish to obtain the pH-responsive polylactic acid-based film (PLA/CGA).
The chitosan is grafted and modified by glycine (Gly) to improve the antibacterial activity of the chitosan and the like. Firstly, 1.5g of chitosan is dissolved in 2 percent (v/v) acetic acid to prepare a chitosan solution; then 1g glycine was slowly added to the chitosan solution and stirred at 65 ℃ for 12 hours; finally, the solution was dried under vacuum at 60 ℃ and ground to obtain the product (CG) in powder form, which was washed several times with ethanol and dried at 50 ℃ until use. The structural formula of CG is as follows:
adding 2-10 wt% of modified chitosan and 0.5-2 wt% of alizarin into a three-neck flask containing a polylactic acid solution at room temperature, and violently stirring for 3-5 hours to ensure that the modified chitosan and the alizarin are uniformly dispersed in the polylactic acid solution.
After the melt blending is finished, pouring the film forming solution into a glass surface dish by a solvent casting method, and drying at room temperature for 24 hours to prepare the pH-responsive polylactic acid-based film.
Example 1
Preparing a polylactic acid/chitosan (PLA/CG) composite film in a bacteriostasis area:
firstly, weighing 1g of PLA, adding the PLA into a beaker containing 30mL of Dichloromethane (DCM), placing the beaker in a constant-temperature ultrasonic reactor, and performing ultrasonic treatment at room temperature to completely dissolve the PLA; then, transferring the molten PLA into a 100ml three-neck flask, adding 2 wt% of modified Chitosan (CG), and magnetically stirring for 2 hours at room temperature to uniformly disperse the CG in the PLA solution; then, 0.25g of tributyl citrate (TBC) is added into the solution, and the solution is magnetically stirred for 1 hour to obtain a film forming solution; and finally, pouring the film forming solution into a glass surface dish with a weight pressed at the circle center, peeling off the weight after overnight film forming at room temperature, and naming the dry film with the round holes as the PLA/CG composite film.
preparation of pH response zone polylactic acid/alizarin (PLA/AL) composite membrane:
firstly, weighing 1g of PLA, adding the PLA into a beaker containing 30mL of DCM, sealing the opening of the beaker, placing the beaker into a constant-temperature ultrasonic reactor, and performing ultrasonic treatment at room temperature to completely dissolve the PLA; then, transferring the molten PLA into a 100ml three-neck flask, adding 0.5 wt% Alizarin (AL), and magnetically stirring for 2h at room temperature to uniformly disperse the AL in the PLA solution; then, adding 0.25g of TBC into the solution, and magnetically stirring for 1h to obtain a film forming solution; and finally, pouring the film forming solution into a circular hole of the PLA/CG composite film, forming a film overnight at room temperature, and naming the dry film filled in the circular hole as the PLA/AL composite film.
Finally, the entire film was peeled from the glass petri dish to obtain a pH-responsive polylactic acid-based film (PLA/CGA).
Example 2
Preparing a polylactic acid/chitosan (PLA/CG) composite film in a bacteriostasis area:
firstly, weighing 1g of PLA, adding the PLA into a beaker containing 25mL of DCM, placing the beaker in a constant-temperature ultrasonic reactor, and performing ultrasonic treatment at room temperature to completely dissolve the PLA; adding 5 wt% of CG into the molten PLA, and magnetically stirring for 3 hours at room temperature; adding 0.25g of TBC into the solution, and magnetically stirring for 1h to obtain a film forming solution; and finally, pouring the film forming solution into a glass surface dish with a weight pressed at the circle center, peeling off the weight after overnight film forming at room temperature, and naming the dry film with the round holes as the PLA/CG composite film.
preparation of pH response zone polylactic acid/alizarin (PLA/AL) composite membrane:
firstly, weighing 1g of PLA, adding the PLA into a beaker containing 25mL of DCM, placing the beaker in a constant-temperature ultrasonic reactor, and performing ultrasonic treatment at room temperature to completely dissolve the PLA; adding 1.5 wt% of AL into the molten PLA, and magnetically stirring for 3 hours at room temperature; adding 0.25g of TBC into the solution, and magnetically stirring for 1h to obtain a film forming solution; and finally, pouring the film forming solution into a circular hole of the PLA/CG composite film, forming a film overnight at room temperature, and naming the dry film filled in the circular hole as the PLA/AL composite film.
Finally, the entire film was peeled from the glass petri dish to obtain a pH-responsive polylactic acid-based film (PLA/CGA).
Example 3
Preparing a polylactic acid/chitosan (PLA/CG) composite film in a bacteriostasis area:
firstly, weighing 1g of PLA, adding the PLA into a beaker containing 20mL of DCM, placing the beaker in a constant-temperature ultrasonic reactor, and performing ultrasonic treatment at room temperature to completely dissolve the PLA; adding 3 wt% of CG into the molten PLA, and magnetically stirring for 3 hours at room temperature; adding 0.25g of TBC into the solution, and magnetically stirring for 1h to obtain a film forming solution; and finally, pouring the film forming solution into a glass surface dish with a weight pressed at the circle center, peeling off the weight after overnight film forming at room temperature, and naming the dry film with the round holes as the PLA/CG composite film.
preparation of pH response zone polylactic acid/alizarin (PLA/AL) composite membrane:
firstly, weighing 1g of PLA, adding the PLA into a beaker containing 20mL of DCM, placing the beaker in a constant-temperature ultrasonic reactor, and performing ultrasonic treatment at room temperature to completely dissolve the PLA; adding 1 wt% of AL into the molten PLA, and magnetically stirring for 3 hours at room temperature; adding 0.25g of TBC into the solution, and magnetically stirring for 1h to obtain a film forming solution; and finally, pouring the film forming solution into a circular hole of the PLA/CG composite film, forming a film overnight at room temperature, and naming the dry film filled in the circular hole as the PLA/AL composite film.
Finally, the entire film was peeled off the glass petri dish to obtain a pH-responsive polylactic acid-based film (PLA/CGA).
Example 4
Preparing a polylactic acid/chitosan (PLA/CG) composite film in a bacteriostasis area:
firstly, weighing 1g of PLA, adding the PLA into a beaker containing 20mL of DCM, placing the beaker in a constant-temperature ultrasonic reactor, and performing ultrasonic treatment at room temperature to completely dissolve the PLA; adding 5 wt% of CG into the molten PLA, and magnetically stirring for 3 hours at room temperature; adding 0.25g of TBC into the solution, and magnetically stirring for 1h to obtain a film forming solution; and finally, pouring the film forming solution into a glass surface dish with a weight pressed at the circle center, peeling off the weight after overnight film forming at room temperature, and naming the dry film with the round holes as the PLA/CG composite film.
preparation of pH response zone polylactic acid/alizarin (PLA/AL) composite membrane:
firstly, weighing 1g of PLA, adding the PLA into a beaker containing 20mL of DCM, placing the beaker in a constant-temperature ultrasonic reactor, and performing ultrasonic treatment at room temperature to completely dissolve the PLA; adding 1 wt% of AL into the molten PLA, and magnetically stirring for 3 hours at room temperature; adding 0.25g of TBC into the solution, and magnetically stirring for 1h to obtain a film forming solution; and finally, pouring the film forming solution into a circular hole of the PLA/CG composite film, forming a film overnight at room temperature, and naming the dry film filled in the circular hole as the PLA/AL composite film.
Finally, the entire film was peeled from the glass petri dish to obtain a pH-responsive polylactic acid-based film (PLA/CGA).
Comparative example 1
Adjusting the using amount of the dichloromethane solvent.
Respectively adding 2 wt% and 0.5 wt% of modified chitosan and alizarin into polylactic acid solution (1g/20mL), vigorously stirring at room temperature for 3h, pouring into a watch glass after the stirring is finished, and standing overnight at room temperature to obtain the pH-responsive polylactic acid-based film.
Comparative example 2
The blending time of the polylactic acid and the functional components is prolonged.
Respectively adding 5 wt% and 1.5 wt% of modified chitosan and alizarin into polylactic acid solution (1g/25mL), vigorously stirring at room temperature for 5h, pouring into a watch glass after the stirring is finished, and standing overnight at room temperature to obtain the pH-responsive polylactic acid-based film.
Comparative example 3
Adjusting the content of functional components.
Respectively adding 5 wt% and 1.5 wt% of modified chitosan and alizarin into a polylactic acid solution (1g/20mL), vigorously stirring at room temperature for 4h, pouring into a watch glass after the stirring is finished, and standing overnight at room temperature to obtain the pH-responsive polylactic acid-based film.
The detailed data are shown in table one
It can be seen from the comparison of examples and comparative examples that the amount of dichloromethane, the content of modified chitosan and alizarin as functional ingredients and the time of melt blending all affect the tensile strength and elongation at break of the pH-responsive polylactic acid-based film. The determination of the optimal solvent dosage, the contents of the modified chitosan and the alizarin and the time of melt blending are the keys for preparing the polylactic acid-based film with excellent performance and pH response.
Fig. 2 shows the antibacterial effect of the polylactic acid film of the PLA and PLA composite film: (a) escherichia coli; (b) staphylococcus aureus. As can be seen from FIG. 2, compared with the pure polylactic acid film, the antibacterial performance of the polylactic acid composite film is improved to different degrees after the modified chitosan and the alizarin are added.
FIG. 3 shows the freshness detection results of chicken breast packaged by PLA and PLA/CGA films and stored for 1-10 days.
FIG. 4 is a graph of the color change response of a PLA/CGA film wrapped chicken breast on the first and tenth days.
The composite membrane prepared by the invention has good mechanical property, pH response and antibiosis, and the polylactic acid-based membrane with pH response is not reported.
It should be noted that the above-mentioned embodiments are only preferred embodiments of the present invention, and the present invention is not limited thereto, and although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that modifications and equivalents can be made in the technical solutions described in the foregoing embodiments, or equivalents thereof. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention. Although the embodiments of the present invention have been described with reference to the accompanying drawings, it is not intended to limit the scope of the present invention, and it should be understood by those skilled in the art that various modifications and variations can be made without inventive efforts by those skilled in the art based on the technical solution of the present invention.
Claims (10)
1. A method for preparing a pH response polylactic acid based composite membrane is characterized by comprising the following steps:
dissolving polylactic acid (PLA) in dichloromethane, uniformly dispersing and melting to obtain molten polylactic acid (PLA);
adding glycine-modified chitosan CG into the molten polylactic acid PLA, uniformly mixing, and adding tributyl citrate TBC to obtain a first film-forming solution;
pouring the first film forming solution into a vessel with a column pressed at the circle center, and after overnight film forming at room temperature, stripping the column to obtain a dry film with round holes, namely a PLA/CG composite film;
taking another part of the molten polylactic acid PLA, adding alizarin AL, uniformly mixing, adding tributyl citrate TBC, and uniformly mixing to obtain a second film forming solution;
and finally, pouring the second film forming solution into a circular cavity of the PLA/CG composite film, forming a film overnight at room temperature to obtain a PLA/AL composite film, and stripping the PLA/AL composite film from a vessel to obtain the PLA/AL composite film.
2. The method for preparing a pH-responsive polylactic acid-based composite membrane according to claim 1, wherein the amount of CG added in the glycine-modified chitosan is 2 to 10 wt% of the PLA.
3. The method for preparing a pH-responsive polylactic acid-based composite membrane according to claim 1, wherein alizarin AL is added in an amount of 0.5-2 wt% based on the molten polylactic acid PLA.
4. The method for preparing a pH-responsive polylactic acid-based composite membrane according to claim 1, wherein the polylactic acid PLA and dichloromethane are used in a ratio of: 1-2 g: 20-40 mL.
5. The preparation method of the pH-responsive polylactic acid-based composite membrane according to claim 1, wherein ultrasonic dispersion is adopted for the dispersion for 1.5-3 hours.
6. The method for preparing the pH-responsive polylactic acid-based composite membrane according to claim 1, wherein the method for preparing the glycine-modified chitosan CG comprises the following steps:
dissolving chitosan in acetic acid to prepare a chitosan solution;
adding glycine into the chitosan solution, carrying out grafting reaction, drying the product solution to obtain powder, washing and drying to obtain the chitosan/glycine/chitosan composite material.
7. The method for preparing a pH-responsive polylactic acid-based composite membrane according to claim 1, wherein the grafting reaction is carried out under a condition of stirring at 65 to 70 ℃ for 12 to 14 hours.
8. A pH-responsive polylactic acid-based composite membrane prepared by the method according to any one of claims 1 to 8.
9. The pH-responsive polylactic acid-based composite membrane according to claim 8, wherein the tensile strength of the composite membrane is 5.7 to 8.1 MPa.
10. The pH-responsive polylactic acid-based composite membrane according to claim 8, wherein the elongation at break of the composite membrane is 6.8 to 30.0%.
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