An intelligent composite film with humidity regulating and antibacterial capabilities, a preparation method and applications thereof

Abstract

The application belongs to the technical field of packaging materials, and particularly relates to a preparation method of an intelligent composite film with humidity regulating and antibacterial capabilities. The method uses hexamethylene diisocyanate, 2,6-pyridine dimethyl alcohol and 1,4-butanediol as raw materials to synthesize a humidity-sensitive polyurethane through a polycondensation reaction; the humidity-sensitive polyurethane is prepared into a humidity-sensitive film through a solution casting method; electrospinning is performed on the humidity-sensitive film as a substrate, and a polylactic acid nanofiber film loaded with an antibacterial active substance is compounded on the upper part of the humidity-sensitive film to form an electrospun layer with antibacterial function, thereby obtaining the intelligent composite film with humidity regulating and antibacterial capabilities. The intelligent composite film prepared by the application has a reasonable structure design and a mature and feasible manufacturing process, and effectively prolongs the shelf life of fruits, vegetables and other foods through the synergistic effect of humidity regulation and antibacterial action, and has a good application prospect.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of packaging materials, and particularly relates to an intelligent composite film with humidity regulating and antibacterial capabilities, a preparation method and application. BACKGROUND

[0002] Fresh-keeping technology is of great significance in reducing fruit and vegetable loss caused by rot, especially in the storage, transportation and sales of fruits and vegetables after picking.

[0003] Humidity plays a crucial role in the storage of fruits and vegetables. Excessive humidity can easily breed bacteria, and water vapor condensation and dripping on the surface of fruits and vegetables can also cause damage; on the other hand, excessive dryness can easily cause fruits to dry up. In addition, fruits and vegetables are also susceptible to bacterial and fungal infections during storage and sale, so the shelf life of fruits and vegetables is very limited, making it difficult to meet the needs of consumers.

[0004] Currently, the preservative film used on the market is mostly polyethylene film (PE), which only has the functions of protecting fruits and vegetables and moisturizing, but does not have the function of regulating humidity. There are also methods of adding bagged moisture-absorbing materials inside the package, but the moisture-absorbing performance of the moisture-absorbing materials is limited. In addition, microporous packaging is also used as a packaging material for fruits and vegetables, but this can cause weight loss of the fruits. The commonly used method of inhibiting bacteria is to spray preservatives, but most of these preservatives are harmful to the human body and the environment, and are not environmentally friendly. SUMMARY

[0005] Based on the above technical problems, the present application provides an intelligent composite film with humidity regulating and antibacterial capabilities, a preparation method and application. The intelligent composite film provided by the present application realizes switching by responding to the humidity change of the external environment through the internal hydrogen bond, thereby realizing the passage and barrier of water vapor molecules inside the package, effectively regulating the humidity inside the package, and providing a new effective way to extend the shelf life of fruits and vegetables.

[0006] In order to achieve the above technical purpose, the present application provides the following technical scheme:

[0007] A preparation method of an intelligent composite film with humidity regulating and antibacterial capabilities, the method comprising the following steps:

[0008] (1) synthesizing a humidity-sensitive polyurethane by condensation reaction with hexamethylene diisocyanate, 2,6-pyridine dimethyl alcohol and 1,4-butanediol as raw materials;

[0009] (2) preparing a humidity-sensitive film by solution casting method with the humidity-sensitive polyurethane;

[0010] (3) electrospinning is performed on the basis of the humidity-sensitive film, a polylactic acid nanofiber film loaded with an antibacterial active substance is compounded on the upper part of the humidity-sensitive film, an electrospun layer with antibacterial function is formed, and a smart composite film with humidity regulating and antibacterial capacity is prepared.

[0011] Further, step (1) is specifically:

[0012] (1.1) 2,6-pyridine dimethyl alcohol is dissolved in a solvent to obtain a clear solution (preferably dissolving at 50°C), hexamethylene diisocyanate is added dropwise under stirring, and the temperature is kept at 50-55°C for 2-3h; this step is an addition polymerization reaction, and the product chemical formula is:

[0013]

[0014] (1.2) hexamethylene diisocyanate and 1,4-butanediol are mixed in a solvent in a certain proportion to obtain a mixed solution, and the mixed solution is added to the reaction system of step (1.1), and the temperature is kept at 50-55°C for 8-10h; the corresponding reaction equation of this step is:

[0015]

[0016] (1.3) the solution after step (2) is vacuum dried to obtain a humidity-sensitive polyurethane.

[0017] Further, in steps (1.1) and (1.2), the solvent used is N,N-dimethylformamide;

[0018] In step (1.1), the liquid ratio of 2,6-pyridine dimethyl alcohol to N,N-dimethylformamide is (3-4):10, unit g / mL; the molar ratio of 2,6-pyridine dimethyl alcohol to hexamethylene diisocyanate is 1:1.

[0019] Further, in step (1.2), the liquid ratio of hexamethylene diisocyanate to N,N-dimethylformamide is (1.5-2):10, unit g / mL;

[0020] The molar ratio of hexamethylene diisocyanate to 1,4-butanediol is 1:1.

[0021] Further, in step (1.1), the molar ratio of 2,6-pyridine dimethyl alcohol to 1,4-butanediol in step (1.2) is (1-2):1.

[0022] Further, in step (1.3), the temperature of the vacuum drying is 60°C, and the time is 24h.

[0023] Further, step (2) is specifically: using N,N-dimethylformamide as a solvent, preparing the humidity-sensitive polyurethane prepared in step (1) into a polymer solution with a mass concentration of 2%-4%, pouring the obtained polymer solution into a mold made of polytetrafluoroethylene through a solution casting method, and placing the mold in a 60 DEG C oven for 24 hours to obtain a humidity-sensitive polyurethane film with a thickness in the range of 50-100 mu m.

[0024] Further, in step (3), the antibacterial active substance includes any one of thymol essential oil, carvacrol, cinnamaldehyde and citral, and the four antibacterial active substances are all non-contact volatile antibacterial substances of natural origin and have good antibacterial effect.

[0025] When electrospinning is performed, when the added antibacterial active substance is thymol essential oil, the mass ratio of thymol essential oil to polylactic acid in the spinning solution is 1:(50-100).

[0026] An intelligent composite film with humidity regulating and antibacterial capabilities is prepared by the preparation method, and the intelligent composite film includes a humidity-sensitive layer and an electrospinning layer; the humidity-sensitive layer is used for realizing the regulation of the humidity inside the package in response to the humidity, and when strawberries are preserved, the humidity can be maintained at 75%-85%;

[0027] The electrospinning layer is loaded with antibacterial active substances, and the antibacterial active substances specifically include any one of thymol essential oil, carvacrol, cinnamaldehyde and citral. The intelligent composite film realizes switching by responding to the change of the humidity in the external environment through internal hydrogen bonds, and can realize the passing and blocking of water vapor molecules inside the package, thereby effectively regulating the humidity inside the package.

[0028] The application of the intelligent composite film with humidity regulating and antibacterial capabilities is applied to the field of food preservation.

[0029] The technical principle of the application is: the humidity regulating function of the intelligent composite film is mainly realized by the "pores" composed of a hydrogen bond system. When the humidity is low (the humidity inside the package is lower than 60%), the molecular chains of the humidity-sensitive polyurethane form intramolecular hydrogen bonds, at this time, the pores are in a closed state, and the water vapor transmission rate is low; when the humidity is high (the humidity inside the package is higher than 60%), water molecules participate in the competition of the hydrogen bond system and form intermolecular hydrogen bonds with the molecular chains, at this time, the pores are opened, and the water vapor transmission rate is increased. Therefore, when the film is used as a packaging material, the opening and closing of the pores can be controlled in response to the humidity inside the package, so as to regulate the humidity inside the package to a relatively suitable environment for the storage of fruits and vegetables.

[0030] The beneficial effects of the application are:

[0031] (1) The intelligent composite film prepared by the method can realize switching by responding to the humidity change of the external environment through the internal hydrogen bond, can realize the passing and blocking of water vapor molecules in the package, and thus effectively regulates the humidity in the package, effectively solves the problem that the fresh-keeping film on the market cannot regulate humidity, etc. The packaging film prepared by the application has reasonable structure design, mature and feasible manufacturing process, effectively prolongs the shelf life of fruits and vegetables and other foods through the synergistic effect of humidity regulation and antibacterial effect, and has good application prospect.

[0032] (2) The antibacterial property of the intelligent composite film prepared by the method is derived from natural materials, has good biocompatibility, and will not produce toxic side effects on the human body.

[0033] (3) The method utilizes the polycondensation reaction to prepare the intelligent composite film with humidity regulation and antibacterial ability, and the antibacterial performance and humidity regulation performance synergistically act, effectively prolonging the storage time of fruits and vegetables. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is the relative molecular mass diagram of the humidity-sensitive polyurethane in the embodiment of the application;

[0035] Figure 2 is a micro-morphology schematic diagram of the intelligent composite film with humidity regulation and antibacterial ability prepared in the embodiment of the application;

[0036] Figure 3 is a humidity response capability schematic diagram of the intelligent composite film with humidity regulation and antibacterial ability prepared in the embodiment of the application;

[0037] Figure 4 is the antibacterial performance of the intelligent composite film with humidity regulation and antibacterial ability prepared in the embodiment of the application;

[0038] Figure 5 is the quality change diagram of strawberries in different experimental groups in the embodiment of the application;

[0039] Figure 6 is the hardness change diagram of strawberries in different experimental groups in the embodiment of the application;

[0040] Figure 7 is the humidity change diagram in different experimental groups in the embodiment of the application;

[0041] Figure 8 is the apparent diagram of strawberries in different experimental groups in the embodiment of the application.

[0042] Figure 9 is a principle diagram of the intelligent composite film regulating humidity in the embodiment of the application. DETAILED DESCRIPTION

[0043] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0044] On the contrary, the present application covers any substitution, modification, equivalent method and scheme defined by the claims within the essence and scope of the present application. Further, in order to make the public have a better understanding of the present application, some specific details are described in detail in the following detailed description of the present application. The present application can also be completely understood without the description of these details by those skilled in the art.

[0045] Example 1

[0046] A preparation method of an intelligent composite film with both humidity regulating and antibacterial abilities, the method comprising the following steps:

[0047] 3g of 2,6-dipyridylmethanol was weighed and dissolved in 10ml of N,N-dimethylformamide at 50°C to obtain a clear solution, 3.5g of hexamethylene diisocyanate was added dropwise to the reaction system under stirring, and the system was placed at 50°C, and reacted for 3h; then 1.5g of hexamethylene diisocyanate and 1g of 1,4-butanediol were mixed in 10ml of N,N-dimethylformamide and added to the reaction system, and the system was placed at 50°C, and reacted for 10h; after the reaction was completed, the system was placed in a vacuum drying box at 60°C for 24h to obtain a humidity-sensitive polyurethane, and the relative molecular weight thereof is shown in Figure 1

[0048] The prepared humidity-sensitive polyurethane was used to prepare a humidity-sensitive film by a solution casting method;

[0049] The humidity-sensitive film was used as a substrate, and a polylactic acid@thymol nanofiber film with a mass ratio of thymol to polylactic acid of 1:50 was compounded with the humidity-sensitive film by electrospinning to prepare an intelligent composite film with both humidity regulating and antibacterial abilities, and the micro-morphology thereof is shown in Figure 2 Figure 9 The humidity regulating principle of the intelligent composite film is shown in

[0050] The water vapor permeability performance of the intelligent film and the preservative film was compared by a weighing method, and the results are shown in Figure 3 The water vapor permeability is similar to that of PE below 60%, and the water vapor permeability changes abruptly above 60%, so the intelligent composite film has excellent humidity response performance. Further research was conducted on the antibacterial effect of the intelligent composite film on Escherichia coli and Staphylococcus aureus, and the results are shown in Figure 4 The intelligent composite film has excellent antibacterial effect on the two bacteria.

[0051] Example 2​​

[0052] A preparation method of an intelligent composite film with humidity regulating and antibacterial capabilities, the method comprising the following steps:

[0053] Weigh 3g of 2,6-dipyridylmethanol and dissolve it in 10ml of N,N-dimethylformamide at 55°C to obtain a clear solution. Add 3.5g of hexamethylene diisocyanate dropwise to the reaction system under stirring, and place the system at 50°C. React for 2h. Then mix 2g of hexamethylene diisocyanate and 1g of 1,4-butanediol in 10ml of N,N-dimethylformamide and add them to the reaction system. Place the system at 50°C. React for 8h. After the reaction is completed, place the system in a vacuum drying box at 60°C for 24h to obtain a humidity-sensitive polyurethane.

[0054] The prepared humidity-sensitive polyurethane is used to prepare a humidity-sensitive film by a solution casting method. A polylactic acid@thymol nanofiber film with a mass ratio of thymol to polylactic acid of 1:50 is compounded with the humidity-sensitive film by electrospinning to obtain an intelligent composite film with humidity regulating and antibacterial capabilities.

[0055] Example 3

[0056] A preparation method of an intelligent composite film with humidity regulating and antibacterial capabilities, the method comprising the following steps:

[0057] Weigh 3g of 2,6-dipyridylmethanol and dissolve it in 10ml of N,N-dimethylformamide at 55°C to obtain a clear solution. Add 3.5g of hexamethylene diisocyanate dropwise to the reaction system under stirring, and place the system at 50°C. React for 2h. Then mix 2g of hexamethylene diisocyanate and 1.5g of 1,4-butanediol in 10ml of N,N-dimethylformamide and add them to the reaction system. Place the system at 55°C. React for 8h. After the reaction is completed, place the system in a vacuum drying box at 60°C for 24h to obtain a humidity-sensitive polyurethane.

[0058] The prepared humidity-sensitive polyurethane is used to prepare a humidity-sensitive film by a solution casting method. A polylactic acid@thymol nanofiber film with a mass ratio of thymol to polylactic acid of 1:50 is compounded with the humidity-sensitive film by electrospinning to obtain an intelligent composite film with humidity regulating and antibacterial capabilities.

[0059] Example 4

[0060] A preparation method of an intelligent composite film with humidity regulating and antibacterial capabilities, the method comprising the following steps:

[0061] Take 3 g of 2,6-dipyridylmethanol and dissolve it in 10 ml of N,N-dimethylformamide at 55°C to obtain a clear solution, add 3.5 g of hexamethylene diisocyanate dropwise to the reaction system under stirring, and place the system at 50°C for 2 h; then mix 2 g of hexamethylene diisocyanate and 1.5 g of 1,4-butanediol in 10 ml of N,N-dimethylformamide and add them to the reaction system, and place the system at 55°C for 8 h; after the reaction is completed, place it in a vacuum drying box at 60°C for 24 h to obtain a moisture-sensitive polyurethane.

[0062] The prepared moisture-sensitive polyurethane is used to prepare a moisture-sensitive film by a solution casting method; the moisture-sensitive film is used as a substrate, and poly-lactic acid@thymol nanofiber film with a mass ratio of thymol to poly-lactic acid of 1:100 is compounded with the moisture-sensitive film by electrospinning to prepare an intelligent composite film with both humidity regulating and antibacterial capabilities.

[0063] The following experiment takes fresh strawberries as the test object, and the strawberries packaged with the intelligent composite film prepared in Example 1 are taken as one group, and the strawberries packaged with a commercially available PE preservative film are taken as a control group.

[0064] At the same time the next day, the mass of each strawberry is taken out and weighed, and the experimental data is recorded, and after the measurement, it is put back into the corresponding packaging. The above experiment is repeated, and the mass of each strawberry is measured continuously for 7 days, and the experimental data is recorded, and a curve graph of the mass of the strawberry changing with time is drawn, as shown in Figure 5 .

[0065] At the same time the next day, the hardness of each strawberry is measured, and the experimental data is recorded, and after the measurement, it is put back into the corresponding packaging. The above experiment is repeated, and the hardness of each strawberry is measured continuously for 7 days, and the experimental data is recorded, and a curve graph of the hardness of the strawberry changing with time is drawn, as shown in Figure 6 .

[0066] The humidity in the two groups of packaging is recorded, and a humidity change curve graph is drawn, as shown in Figure 7 . Figure 8

[0067] As can be seen from Figure 5 , the mass of the strawberry decreases day by day, and the mass decrease rate of the strawberry in the intelligent composite film group is roughly the same as that in the commercially available PE preservative film group, and according to the mass change index, it is indicated that the intelligent composite film has a good fresh-keeping effect on the strawberry.

[0068] As can be seen from Figure 6 ​As can be seen, the firmness of both groups of strawberries decreased. The strawberries packaged with the smart composite film showed a relatively slower decrease in firmness, while the strawberries packaged with commercially available PE preservation film showed a significant decrease in firmness. Based on the hardness index, it can be seen that the smart composite film has a certain degree of preservation effect on strawberries.

[0069] Depend on Figure 7 As can be seen, under the same storage conditions, the humidity inside the smart composite film packaging is significantly lower than that of commercially available PE preservation film, thus proving that the smart composite film can effectively regulate the humidity inside the packaging.

[0070] The degree of rot of strawberries as Figure 8 As shown in the figure above, the strawberries in the commercially available PE preservation film group showed obvious signs of rotting on the seventh day, while the strawberries in the smart composite film group remained relatively fresh on the seventh day. This proves that the smart composite film has a better preservation effect on strawberries.

[0071] Therefore, it is evident that the intelligent composite film provided by this invention can effectively maintain the freshness of strawberries and extend the storage period of the fruit.

[0072] This invention discloses a method for preparing a smart composite film with both humidity-regulating and antibacterial capabilities, and its application in simulating strawberry preservation, belonging to the field of packaging materials technology. First, a moisture-sensitive polyurethane is synthesized via a polycondensation reaction using hexamethylene diisocyanate, 2,6-pyridinediethanol, and 1,4-butanediol as raw materials. Then, it is formed into a film using a solution casting method. Finally, the moisture-sensitive film is used as a substrate for electrospinning to obtain a smart composite film composed of the moisture-sensitive film and a polylactic acid nanofiber film loaded with thymol essential oil. The moisture-sensitive layer can regulate the humidity inside the packaging in response to humidity, while the thymol essential oil loaded in the electrospun layer imparts good antibacterial properties to the packaging film. The resulting smart composite film effectively extends the shelf life of fruits and vegetables through a synergistic effect of humidity regulation and antibacterial properties. The packaging film obtained by this invention has a reasonable structural design and mature manufacturing process, and can be widely used for the preservation of humidity-sensitive fruits and vegetables, showing good application prospects.

[0073] The foregoing description illustrates and describes several preferred embodiments of this application. However, as previously stated, it should be understood that this application is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the application concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of this application should be within the protection scope of the appended claims.

Claims

1. A method for preparing a smart composite film with both humidity regulating and antibacterial capabilities, characterized in that, The method includes the following steps: (1) Moisture-sensitive polyurethane was synthesized by polycondensation reaction using hexamethylene diisocyanate, 2,6-pyridinediethanol and 1,4-butanediol as raw materials; (2) The moisture-sensitive polyurethane is used to prepare a moisture-sensitive film by solution casting. (3) Electrospinning is performed on the moisture-sensitive film as a substrate to composite the polylactic acid nanofiber membrane loaded with antibacterial active substances on the upper part of the moisture-sensitive film to form an electrospun layer with antibacterial function, thereby obtaining an intelligent composite film with both humidity regulation and antibacterial capabilities. Step (1) is as follows: (1.1) Dissolve 2,6-pyridinediethanol in a solvent to obtain a clear solution, add hexamethylene diisocyanate dropwise with stirring, and keep warm at 50°C for 2-3 h; (1.2) Mix hexamethylene diisocyanate and 1,4-butanediol in a solvent in a certain proportion to obtain a mixed solution. Add the mixed solution to the reaction system of step (1.1) and keep it at 50°C for 8-10 h. (1.3) After the reaction in step (1.2) is completed, the solution is dried under vacuum to obtain a moisture-sensitive polyurethane. In steps (1.1) and (1.2), the solvent used is N,N-dimethylformamide; In step (1.1), the ratio of 2,6-pyridinediethanol and N,N-dimethylformamide is (3-4):10, in g / mL, and the molar ratio of 2,6-pyridinediethanol to hexamethylene diisocyanate is 1:

1. In step (1.2), the ratio of hexamethylene diisocyanate to N,N-dimethylformamide is (1.5-2):10, in g / mL, and the molar ratio of hexamethylene diisocyanate to 1,4-butanediol is 1:

1.

2. The method for preparing a smart composite film with both humidity regulation and antibacterial capabilities according to claim 1, characterized in that, In step (1.1), the molar ratio of 2,6-pyridinediethanol to 1,4-butanediol in step (1.2) is (1~2):

1.

3. The method for preparing a smart composite film with both humidity regulation and antibacterial capabilities according to claim 1, characterized in that, In step (1.3), the vacuum drying temperature is 60°C and the time is 24 h.

4. The method for preparing a smart composite film with both humidity regulation and antibacterial capabilities according to claim 1, characterized in that, Step (2) specifically involves: using N,N-dimethylformamide as a solvent, preparing the moisture-sensitive polyurethane obtained in step (1) into a polymer solution with a mass concentration of 2%-4%, and casting the obtained polymer solution into a polytetrafluoroethylene mold by solution casting method, and placing it in a 60℃ oven for 24 hours to obtain a moisture-sensitive polyurethane film with a thickness range of 50-100μm.

5. The method for preparing a smart composite film with both humidity regulation and antibacterial capabilities according to claim 1, characterized in that, In step (3), the antibacterial active substance includes any one of thymol essential oil, carvacrol, cinnamaldehyde and citral; When electrospinning, if the added antibacterial active substance is thymol essential oil, the mass ratio of thymol essential oil to polylactic acid in the spinning solution is 1:(50~100).

6. A smart composite film possessing both humidity-regulating and antibacterial capabilities, prepared using the preparation method described in any one of claims 1-5, characterized in that, The smart composite film includes a humidity-sensitive layer and an electrospun layer; the humidity-sensitive layer is used to regulate the humidity inside the packaging in response to humidity.

7. An application of the intelligent composite film with both humidity regulation and antibacterial capabilities as described in claim 6, characterized in that, The intelligent composite film is applied to the field of food preservation.

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