A method for preparing a multifunctional polylactic acid active packaging composite film

Abstract

The present invention provides a method for preparing a multifunctional polylactic acid active packaging composite film, the preparation method comprising: (1) enclosing cinnamaldehyde in a hydrophobic cavity of hydroxypropyl-β-cyclodextrin, and then cross-linking with cellulose citrate and anthocyanidin; (2) using a pure polylactic acid film as a substrate, compounding the cross-linking system obtained in (1) with polylactic acid by electrospinning; and (3) reacting tannic acid with the composite film prepared in (2) through a host-guest interaction to obtain a multifunctional polylactic acid active packaging composite film. The composite packaging film has multiple functions such as antibacterial properties, antioxidant properties, and intelligent color development, and has improved tensile strength, thereby effectively improving the functions of the polylactic acid film.

Description

Technical Field

[0001] The invention relates to a method for preparing a packaging composite film, in particular to a method for preparing a multifunctional polylactic acid active packaging composite film. Background Art

[0002] Polylactic acid (PLA) is a new type of biodegradable material made from starch extracted from renewable plant resources (such as corn). The starch is saccharified to produce glucose, which is then fermented with a specific bacterial strain to produce high-purity lactic acid. Polylactic acid is then synthesized to a specific molecular weight through chemical synthesis. It exhibits excellent biodegradability and is completely degraded by natural microorganisms after use, ultimately producing carbon dioxide and water. It is a recognized environmentally friendly material and exhibits excellent safety and biocompatibility.

[0003] However, although PLA films made from a single PLA raw material have good mechanical and physical properties, including good tensile strength and ductility, their functionality is relatively limited and cannot meet the requirements for high-efficiency antibacterial and antioxidant activity, providing excellent protection for food against microbial deterioration and oxidation, and extending the shelf life of food.

[0004] Polymer packaging film, as a barrier between the material itself and the external environment, can change the properties (hydrophilicity, crystallinity, permeability and biocompatibility, etc.) of the surface by modifying the surface structure. Electrostatic spinning is one of the simplest technologies for incorporating nanofillers into polymer nanofibers, and the composite film prepared by electrostatic spinning has the advantage of loadability. Therefore, the present invention adopts electrostatic spinning and solvent casting method to combine to prepare polylactic acid active packaging film composite film, and polylactic acid is subjected to surface modification to achieve multifunctional loading. Summary of the Invention

[0005] In order to solve the problem of single function of polylactic acid film, the present invention provides a method for preparing a multifunctional polylactic acid active packaging composite film, which realizes the multifunctional loading of the polylactic acid active packaging film.

[0006] In order to achieve the above technical objectives, the technical solution adopted by the present invention is: a method for preparing a multifunctional polylactic acid active packaging composite film, characterized in that:

[0007] The preparation method comprises the following steps: (1) encapsulating cinnamaldehyde in a hydrophobic cavity of hydroxypropyl-β-cyclodextrin, wherein the cavity of the hydroxypropyl-β-cyclodextrin is hydrophobic and the outside of the cavity is hydrophilic; cross-linking cellulose citrate and anthocyanin to obtain a cross-linked system of hydroxypropyl-β-cyclodextrin, cellulose citrate and anthocyanin; (2) using a pure polylactic acid film as a substrate, compounding the cross-linked system obtained in (1) with polylactic acid by electrostatic spinning; and (3) subjecting tannic acid to a host-guest interaction with the composite film prepared in (2) to obtain a host-guest self-polymerized composite film constructed of hydroxypropyl-β-cyclodextrin, cellulose citrate, anthocyanin and tannic acid, i.e., a multifunctional polylactic acid active packaging composite film.

[0008] Furthermore, the method specifically comprises the following steps:

[0009] (a) mixing hydroxypropyl-β-cyclodextrin and water, stirring at a certain temperature for 1 to 2 hours, and then stirring at room temperature for half an hour to obtain a clear and transparent hydroxypropyl-β-cyclodextrin aqueous solution;

[0010] (b) adding cinnamaldehyde in step (a) at a molar ratio of 1:1 to hydroxypropyl-β-cyclodextrin, stirring at room temperature for 12 to 36 hours, and then standing to remove bubbles;

[0011] (c) 3 mL of the solution obtained in step (b) was measured and added with ground and sieved cellulose citrate, and the mixture was stirred at room temperature to obtain a uniform mixed solution;

[0012] (d) adding 2 mL of anthocyanidin 50% ethanol aqueous solution to the mixed solution of step (c), stirring at 20-30° C. until a uniform mixed solution is obtained, and then sonicating for 10-20 minutes to remove bubbles in the solution;

[0013] (e) 10 mL of the solution from step (d) was drawn for electrospinning, and the pure polylactic acid film was fixed on a homemade roller collector to collect the electrospun fibers;

[0014] (f) preparing a 0.05-0.2 g / mL tannic acid aqueous solution, spraying the solution evenly on the polylactic acid composite film prepared in step (e), and then drying the film. Repeat this process three times.

[0015] Furthermore, in step (a), the mass ratio of hydroxypropyl-β-cyclodextrin to water is 240% to 320%; and the reaction temperature is 40 to 60°C.

[0016] Furthermore, the mass of the cellulose citrate in step (c) is 0.1 to 0.2 g.

[0017] Furthermore, in the step (d), the concentration of the anthocyanidin 50% ethanol aqueous solution is 0.2-0.3 g / mL.

[0018] Furthermore, the specific method of electrospinning in step (e) is as follows: 10 mL of the cross-linking solution in step (d) is added to a 10 mL syringe, the syringe is connected to a 23G pure metal electrospinning needle as a nozzle (inner diameter 0.33 mm, outer diameter 0.63 mm), the distance between the collector and the needle is 10 to 15 cm, the flow rate of the precision injection pump is 0.5 mL / h, the electrospinning high voltage is controlled within 15 kV, the substrate pure polylactic acid film is fixed on a homemade roller, and the spun fibers are continuously covered and collected.

[0019] Beneficial effects of the present invention:

[0020] (1) The present invention utilizes the non-polar hydrophobic cavity and hydrophilic outer surface molecular chain of the amphiphilic substance hydroxypropyl-β-cyclodextrin, and introduces hydrophobic cinnamaldehyde into the hydrophobic cavity to form an inclusion compound. Hydroxypropyl-β-cyclodextrin and cinnamaldehyde interact to form hydrogen bonds and van der Waals forces, and the inclusion compound can be stably present in the hydrophilic system;

[0021] (2) Hydroxypropyl-β-cyclodextrin, cellulose citrate and anthocyanidin are cross-linked through hydrogen bonding to achieve the slow release of the antibacterial active substance cinnamaldehyde, while also having intelligent color development;

[0022] (3) Through the strong hydrogen bonding effect of the antioxidant active substance tannic acid, the polylactic acid composite film has antioxidant properties and increases its tensile strength;

[0023] (4) The raw materials of the present invention are natural and non-toxic, the preparation process is green and environmentally friendly, and has little negative impact on the environment. The modified pure polylactic acid film has multifunctional properties such as antibacterial, antioxidant, and intelligent color development, and has improved tensile strength, effectively improving the functionality of the pure polylactic acid film and the sustained release of active substances. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 These are electron micrographs of the multifunctional polylactic acid active packaging composite films of the present invention, including scanning electron micrographs of (a) PLA-0, (b) PLA-0 / TA, (c) PLA-1, (d) PLA-1 / TA, (e) PLA-2, (f) PLA-2 / TA, (g) PLA-3, (h) PLA-3 / TA, (i) PLA-4, and (j) PLA-4 / TA.

[0025] Figure 2 Stress-strain curves of multifunctional polylactic acid active packaging composite films, where (a) is the stress-strain curve of the PLA composite film without TA surface cross-linking treatment, and (b) is the stress-strain curve of the PLA composite film after TA surface cross-linking treatment. DETAILED DESCRIPTION

[0026] The present invention will be further described below in conjunction with specific examples. These examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, after reading the content taught by the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalents also fall within the scope defined by the appended claims of the application.

[0027] Example 1

[0028] (a) mixing hydroxypropyl-β-cyclodextrin and water in a mass ratio of 240%, stirring at 40° C. for 1 hour, and then stirring at room temperature for half an hour to obtain a clear hydroxypropyl-β-cyclodextrin aqueous solution;

[0029] (b) adding cinnamaldehyde in step (a) at a molar ratio of 1:1 to hydroxypropyl-β-cyclodextrin, stirring at room temperature for 24 hours, and then standing to remove bubbles;

[0030] (c) 3 mL of the solution obtained in step (b) was measured, 0.12 g of ground and sieved cellulose citrate was added, and the mixture was stirred at room temperature to obtain a uniform mixed solution;

[0031] (d) adding 2 mL of 0.22 g / mL anthocyanidin 50% ethanol aqueous solution to the mixed solution of step (c), stirring at 20° C. until a uniform mixed solution is obtained, and then sonicating for 15 minutes to remove bubbles in the solution;

[0032] (e) The solution obtained in step (d) was drawn into a 10 mL syringe, and the polymer solution was added to the 10 mL syringe connected to a 23 G needle as a nozzle. The distance between the collector and the needle was approximately 10 cm. The flow rate was set to 0.5 mL / h by a precision pump, and the electrospinning voltage was controlled within 15 kV by a high-voltage stator.

[0033] The pure polylactic acid film was fixed on a homemade roller collector to collect the fibers and obtain PLA-0, such as Figure 1 (a) Prepare 0.1 g / mL tannic acid TA aqueous solution, spray it evenly on the polylactic acid composite film in step (e), and then dry it. Repeat three times to obtain a composite film PLA-0 / TA. Figure 1 (b).

[0034] Example 2

[0035] (a) mixing hydroxypropyl-β-cyclodextrin and water in a mass ratio of 260%, stirring at 45° C. for 1 hour, and then stirring at room temperature for half an hour to obtain a clear hydroxypropyl-β-cyclodextrin aqueous solution;

[0036] (b) adding cinnamaldehyde in step (a) at a molar ratio of 1:1 to hydroxypropyl-β-cyclodextrin, stirring at room temperature for 24 hours, and then standing to remove bubbles;

[0037] (c) 3 mL of the solution obtained in step (b) was measured, 0.14 g of ground and sieved cellulose citrate was added, and the mixture was stirred at room temperature to obtain a uniform mixed solution;

[0038] (d) 2 mL of 0.24 g / mL anthocyanidin 50% ethanol aqueous solution was added to the mixed solution of step (c), and the mixture was stirred at 20° C. until a uniform mixed solution was obtained. The mixture was then sonicated for 15 minutes to remove bubbles in the solution.

[0039] (e) The solution obtained in step (d) was drawn into a 10 mL syringe, and the polymer solution was added to the 10 mL syringe connected to a 23 G needle as a nozzle. The distance between the collector and the needle was approximately 10 cm. The flow rate was set to 0.5 mL / h by a precision pump, and the electrospinning voltage was controlled within 15 kV by a high-voltage stator.

[0040] The pure polylactic acid film was fixed on a homemade roller collector to collect the fibers and obtain PLA-1. Figure 1 (c) Prepare a 0.1 g / mL tannic acid aqueous solution and spray it evenly on the polylactic acid composite film in step (e), then dry it. Repeat this process three times to obtain a composite film PLA-1 / TA. Figure 1 (d).

[0041] Example 3

[0042] (a) mixing hydroxypropyl-β-cyclodextrin and water in a mass ratio of 280%, stirring at 55° C. for 1 hour, and then stirring at room temperature for half an hour to obtain a clear hydroxypropyl-β-cyclodextrin aqueous solution;

[0043] (b) adding cinnamaldehyde in step (a) at a molar ratio of 1:1 to hydroxypropyl-β-cyclodextrin, stirring at room temperature for 24 hours, and then standing to remove bubbles;

[0044] (c) 3 mL of the solution obtained in step (b) was measured, 0.16 g of ground and sieved cellulose citrate was added, and the mixture was stirred at room temperature to obtain a uniform mixed solution;

[0045] (d) adding 2 mL of a 0.26 g / mL anthocyanidin 50% ethanol aqueous solution to the mixed solution of step (c), stirring at 20° C. until a uniform mixed solution is obtained, and then sonicating for 15 minutes to remove bubbles in the solution;

[0046] (e) The solution obtained in step (d) was drawn into a 10 mL syringe, and the polymer solution was added to a 10 mL syringe connected to a 23 G needle nozzle. The distance between the collector and the needle was approximately 10 cm. The flow rate was set to 0.5 mL / h by a precision pump, and the electrospinning voltage was controlled within 15 kV by a high-voltage stator.

[0047] The pure polylactic acid film was fixed on a homemade roller collector to collect the fibers and obtain PLA-2 Figure 1 (e) Prepare a 0.1 g / mL tannic acid aqueous solution and spray it evenly on the polylactic acid composite film in step (e), then dry it. Repeat this process three times to obtain a composite film PLA-2 / TA. Figure 1 (f).

[0048] Example 4

[0049] (a) mixing hydroxypropyl-β-cyclodextrin and water in a mass ratio of 300%, stirring at 60° C. for 1 hour, and then stirring at room temperature for half an hour to obtain a clear and transparent hydroxypropyl-β-cyclodextrin aqueous solution;

[0050] (b) adding cinnamaldehyde in step (a) at a molar ratio of 1:1 to hydroxypropyl-β-cyclodextrin, stirring at room temperature for 24 hours, and then allowing to stand to remove bubbles.

[0051] (c) 3 mL of the solution obtained in step (b) was measured, 0.18 g of ground and sieved cellulose citrate was added, and the mixture was stirred at room temperature to obtain a uniform mixed solution;

[0052] (d) adding 2 mL of 0.28 g / mL anthocyanidin 50% ethanol aqueous solution to the mixed solution of step (c), stirring at 20° C. until a uniform mixed solution is obtained, and then sonicating for 15 minutes to remove bubbles in the solution;

[0053] (e) The solution obtained in step (d) was drawn into a 10 mL syringe, and the polymer solution was added to the 10 mL syringe connected to a 23 G needle as a nozzle. The distance between the collector and the needle was approximately 10 cm. The flow rate was set to 0.5 mL / h by a precision pump, and the electrospinning voltage was controlled within 15 kV by a high-voltage stator.

[0054] The pure polylactic acid film was fixed on a homemade roller collector to collect the fibers and obtain PLA-3 Figure 1 (g) Prepare 0.1 g / mL tannic acid aqueous solution, spray it evenly on the polylactic acid composite film in step (e), and then dry it. Repeat three times to obtain a composite film PLA-3 / TA. Figure 1 (h).

[0055] Example 5

[0056] (a) mixing hydroxypropyl-β-cyclodextrin and water in a mass ratio of 320%, stirring at 60° C. for 1 hour, and then stirring at room temperature for half an hour to obtain a clear hydroxypropyl-β-cyclodextrin aqueous solution;

[0057] (b) adding cinnamaldehyde in step (a) at a molar ratio of 1:1 to hydroxypropyl-β-cyclodextrin, stirring at room temperature for 24 hours, and then standing to remove bubbles;

[0058] (c) 3 mL of the solution obtained in step (b) was measured, 0.18 g of ground and sieved cellulose citrate was added, and the mixture was stirred at room temperature to obtain a uniform mixed solution;

[0059] (d) 2 mL of 0.28 g / mL anthocyanidin 50% ethanol aqueous solution was added to the mixed solution of step (c), and the mixture was stirred at 20° C. until a uniform mixed solution was obtained, and then ultrasonicated for 15 minutes to remove bubbles in the solution.

[0060] (e) The solution obtained in step (d) was drawn into a 10 mL syringe, and the polymer solution was added to the 10 mL syringe connected to a 23 G needle as a nozzle. The distance between the collector and the needle was approximately 10 cm. The flow rate was set to 0.5 mL / h by a precision pump, and the electrospinning voltage was controlled within 15 kV by a high-voltage stator.

[0061] The pure polylactic acid film was fixed on a homemade roller collector to collect the fibers and obtain PLA-4 Figure 1 (i) Prepare a 0.1 g / mL tannic acid aqueous solution and spray it evenly on the polylactic acid composite film in step (e), then dry it. Repeat this process three times to obtain a composite film PLA-4 / TA. Figure 1 (j).

[0062] β-cyclodextrin (β-CD) has a unique cavity structure that allows it to form inclusion complex emulsion droplets with cinnamaldehyde essential oil molecules. However, the β-CD emulsion droplets easily flocculate, leading to phase separation in the system, which is not conducive to the formation of electrospun fibers. This phase separation also accelerates the volatilization of cinnamaldehyde essential oil, seriously affecting its sustained release and antibacterial effect. The addition of a certain amount of cellulose citrate (CNC) effectively inhibited the flocculation of the β-CD emulsion.

[0063] from Figure 1It can be seen that with the increase of β-CD concentration, the electrospun structure changes from spherical beads to smooth and elongated spherical fibers. Finally, the surface is cross-linked with cyclodextrin by spraying tannic acid. Low concentrations of β-CD have insufficient aggregates, which leads to instability of the charged jet during electrospinning, resulting in beads rather than continuous fibers. Higher concentrations of β-CD increase the number of aggregates and the polymer solution has more chain entanglements, resulting in complete stretching of the charged solution jet, thus producing bead-free nanofibers.

[0064] Figure 2 The stress and strain comparison of the three membranes are: pure PLA membrane; PLA matrix, hydroxypropyl-β-cyclodextrin, acetylated cellulose citrate, anthocyanin cross-linked electrospinning system composite membrane; and PLA matrix, hydroxypropyl-β-cyclodextrin, acetylated cellulose citrate, anthocyanin, tannic acid cross-linked electrospinning system composite membrane. It can be concluded from the figure that with the increase of β-CD concentration, the electrospinning jet changes from beads to fibers, increasing entanglement and stacking; more importantly, the strong hydrogen bonding effect between tannic acid and β-CD host and guest is enhanced, thereby effectively improving the mechanical properties of the composite membrane.

Claims

1. A method for preparing a multifunctional polylactic acid active packaging composite film, characterized in that: The preparation method comprises (1) Cinnamaldehyde is encapsulated in the hydrophobic cavity of hydroxypropyl-β-cyclodextrin, wherein the cavity of hydroxypropyl-β-cyclodextrin is hydrophobic and the outside of the cavity is hydrophilic; Then cross-linking with cellulose citrate and anthocyanin to obtain a hydroxypropyl-β-cyclodextrin, cellulose citrate, anthocyanin cross-linking system; (2) Using pure polylactic acid film as a substrate, the cross-linking system obtained in (1) is composited with polylactic acid by electrospinning; (3) Tannic acid is then reacted with the composite film prepared in (2) through host-guest interaction to obtain a host-guest self-polymerization composite film constructed of hydroxypropyl-β-cyclodextrin, cellulose citrate, anthocyanin and tannic acid, namely, a multifunctional polylactic acid active packaging composite film.

2. The preparation method according to claim 1, wherein The preparation method specifically comprises the following steps: (a) mixing hydroxypropyl-β-cyclodextrin and water in a certain mass ratio, stirring at a certain temperature for 1 to 2 hours, and then stirring at room temperature for half an hour to obtain a clear and transparent hydroxypropyl-β-cyclodextrin aqueous solution; (b) adding cinnamaldehyde at a molar ratio of 1:1 to hydroxypropyl-β-cyclodextrin in step (a), stirring at room temperature for 12 to 36 hours, and then standing to remove bubbles; (c) 3 mL of the solution obtained in step (b) was added to the ground and sieved cellulose citrate, and the mixture was stirred at room temperature to obtain a uniform mixed solution; (d) Add 2 mL of anthocyanin 50% ethanol aqueous solution to the mixed solution from step (c) and stir at 20-30°C until a uniform mixed solution is obtained. Then, sonicate for 10-20 minutes to remove bubbles in the solution. (e) 10 mL of the solution from step (d) was aspirated for electrospinning, and the pure PLA film was fixed on a homemade roller collector to collect the electrospun fibers; (f) Prepare a 0.05-0.2 g / mL tannic acid aqueous solution, spray it evenly on the polylactic acid composite film in step (e), and then dry it. Repeat this process three times.

3. The preparation method according to claim 2, wherein In step (a), the mass ratio of hydroxypropyl-β-cyclodextrin to water is 240% to 320%; and the reaction temperature is 40° C. to 60° C.

4. The preparation method according to claim 3, wherein The mass of the cellulose citrate in the step (c) is 0.1 to 0.2 g.

5. The preparation method according to claim 4, wherein: The concentration of the anthocyanin 50% ethanol aqueous solution in step (d) is 0.2-0.3 g / mL.

6. The preparation method according to any one of claims 2 to 5, wherein The specific method of electrospinning in step (e) is as follows: 10 mL of the cross-linking solution in step (d) is added to a 10 mL syringe, the syringe is connected to a 23-gauge pure metal electrospinning needle as a nozzle, the distance between the collector and the needle is 10 to 15 cm, the flow rate of the precision syringe pump is 0.5 mL / h, the electrospinning high voltage is controlled within 15 kV, the substrate pure polylactic acid film is fixed on a homemade roller, and the spun fibers are continuously covered and collected.

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