Intelligent humidity control film with temperature and humidity dual response, preparation method and application thereof

Abstract

The application belongs to the technical field of packaging materials, and discloses an intelligent humidity regulating film with temperature and humidity dual response, a preparation method and application of the intelligent humidity regulating film. The temperature response system of the packaging material is from poly(N-isopropyl acrylamide), and the humidity response system is from humidity response polyurethane. The intelligent humidity regulating film with temperature and humidity dual response is successfully prepared through a condensation reaction and a solution casting method. The intelligent humidity regulating film prepared in the application can realize temperature and humidity dual "switch" regulation of the humidity inside the material, the humidity response threshold is 60%, and the temperature response threshold is 31 DEG C. The surface of the material is loaded with antibacterial substances, and the application is applied to the field of fruit and vegetable preservation, so that the film material has humidity regulating and antibacterial properties; the film loaded with the antibacterial substances has good preservation and preservation effect. The temperature and humidity dual response intelligent humidity regulating film has a mature and feasible production process, and has high application value in the future in the technical field of packaging materials.

Description

Technical Field

[0001] This invention belongs to the field of packaging materials technology, specifically relating to a smart humidity-regulating film with dual temperature and humidity responses, its preparation method, and its application. Background Technology

[0002] Every year, 200 million tons of fruits and vegetables are lost, resulting in economic losses of 75 billion yuan. Consuming rotten fruits and vegetables can easily lead to food poisoning, and may even cause coma and endanger the lives of consumers; efficient and low-cost post-harvest preservation of fruits and vegetables has always been one of the most pressing problems to be solved in the food industry.

[0003] Fruit and vegetable sweating refers to the phenomenon of water droplets condensing on the inner surface of packaging materials during the post-harvest storage, transportation, and sales of fruits and vegetables. This is mainly because fruits and vegetables are still living organisms after harvesting, and respiration and transpiration continue, producing moisture. When storing with traditional plastic wrap materials, which have poor air and moisture permeability, high humidity and temperature differences can lead to fogging and condensation inside the packaging. When the humidity is too high, bacteria can easily grow, and water droplets falling on the surface of fruits and vegetables accelerate spoilage, significantly shortening their shelf life.

[0004] Currently, most food preservation film materials on the market are polyethylene (PE) film, polyvinyl chloride (PVC) film, polyvinylidene chloride (PVDC) film, etc. Although they can reduce physical damage to fruits and vegetables, they have high barrier properties to water vapor and do not have any humidity regulation properties, which can easily lead to excessive humidity.

[0005] Patent application number 202311538918.7 discloses a smart composite film with both humidity regulation and antibacterial capabilities, its preparation method, and its application. While the smart composite film disclosed in this patent can achieve humidity regulation and antibacterial properties, it cannot responsively adjust humidity in response to ambient temperature. The respiration and transpiration of fruits are significantly affected by ambient temperature. At higher temperatures, the respiration and transpiration of fruits and vegetables intensify, leading to excessively high humidity inside the packaging material. Therefore, under high temperature conditions, the humidity inside the packaging material also increases sharply. Thus, relying solely on humidity response to regulate the humidity inside the packaging is insufficient. Therefore, this invention introduces a dual-response humidity regulation method under complex environments, enabling the packaging material to achieve multiple stimulus responses to regulate humidity. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a smart humidity-regulating film with dual temperature and humidity responses, its preparation method, and its applications. The smart film provided by this invention regulates humidity inside packaging through dual temperature and humidity stimuli responses. Firstly, it switches on and off in response to changes in external humidity via internal hydrogen bonds. Secondly, it switches on and off in response to temperature changes via internal temperature-sensitive polymer chains. This allows for the passage and blocking of water vapor molecules inside the packaging, thereby effectively regulating the humidity within the packaging.

[0007] The technical solution adopted in this invention is as follows:

[0008] A method for preparing a smart humidity-regulating film with dual temperature and humidity responses, the method comprising the following steps:

[0009] (1) A temperature-responsive polymer is added during the synthesis of humidity-responsive polyurethane to obtain a polymer solution in which the temperature-responsive polymer and humidity-responsive polyurethane are mixed.

[0010] (2) The polymer solution obtained in step (1) is deposited by solution casting to obtain a smart humidity control film with dual temperature and humidity response.

[0011] Furthermore, the temperature-responsive polymer used in step (1) is poly(N-isopropylacrylamide).

[0012] Furthermore, step (1) specifically includes:

[0013] (1.1) Dissolve 2,6-pyridinediethanol in a solvent and stir to obtain a clear solution. Add hexamethylene diisocyanate dropwise under constant temperature of 45-55℃ water bath with stirring, and keep stirring at constant temperature for 1-2 hours.

[0014] (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 warm in a water bath at 45-55℃.

[0015] (1.3) Dissolve poly(N-isopropylacrylamide) in a solvent and stir to obtain a clear solution of poly(N-isopropylacrylamide), which is the PNIPAM solution;

[0016] (1.4) The PNIPAM solution obtained in step (1.3) is added to the reaction system in step (1.2) and reacted for 6-8 hours to obtain a polymer solution in which temperature-responsive polymer and humidity-responsive polyurethane are mixed.

[0017] Furthermore, in steps (1.1), (1.2), and (1.3), the solvent used is N,N-dimethylformamide;

[0018] In step (1.1), the ratio of 2,6-pyridinediethanol to solvent is (2-3):10, in g / mL; the mass ratio of 2,6-pyridinediethanol to hexamethylene diisocyanate is (4-6):7.

[0019] In step (1.2), the mass ratio of hexamethylene diisocyanate to 1,4-butanediol is 2:1; the material-to-liquid ratio of hexamethylene diisocyanate to solvent is 9:50, in g / mL.

[0020] In step (1.3), the ratio of poly(N-isopropylacrylamide) to solvent is 3:20, in g / mL.

[0021] Further, in step (1.1), the mass ratio of 2,6-pyridinediethanol to 1,4-butanediol in step (1.2) is (20-30):9;

[0022] In the reaction system of step (1.4), the mass ratio of poly(N-isopropylacrylamide) to the total mass of hexamethylene diisocyanate, 2,6-pyridinediethanol and 1,4-butanediol is 3:82-92.

[0023] Further, step (2) specifically involves: using a solution casting method, the polymer solution obtained in step (1) is spread evenly on a glass plate using a film-laying machine, and placed in an oven at 40-60℃ for 15-24 hours to obtain a smart humidity-regulating film with dual temperature and humidity response.

[0024] Furthermore, the thickness of the temperature-humidity dual-response conditioning film prepared in step (2) is 20-50 μm.

[0025] Furthermore, the method also includes step (3): loading antibacterial substances onto the surface of the intelligent humidity-regulating film obtained in step (2) to obtain an intelligent humidity-regulating film that has antibacterial properties, temperature regulation properties and humidity regulation properties.

[0026] The loading method is as follows: spray a tea polyphenol solution with a concentration of (1-4) g / L onto the inner side of the humidity-regulating film for antibacterial treatment.

[0027] A smart humidity-regulating film with dual temperature and humidity responses, wherein the smart humidity-regulating film regulates the internal humidity of packaging materials through dual temperature and humidity responses; the humidity response threshold of the smart humidity-regulating film is 60%, and the temperature response threshold is 31°C.

[0028] An application of a smart humidity-regulating film with both temperature and humidity responses, possessing both humidity-regulating and antibacterial capabilities, is described, applying the smart humidity-regulating film in the field of food preservation.

[0029] The technical principle of this invention is as follows: The humidity control function of the temperature and humidity dual-response intelligent humidity regulating film provided by this invention mainly consists of two "switches" for temperature and humidity control. When the humidity is low (the internal humidity of the packaging material is below 60%), the polymer chains of the humidity-responsive polyurethane can form intramolecular hydrogen bonds, causing the polymer chains to be tightly packed together. The humidity-responsive switch is closed, hindering the passage of water molecules. When the humidity is high (the internal humidity of the packaging material is greater than 60%), water molecules participate in the hydrogen bond competition within the humidity-responsive system. The intramolecular hydrogen bonds between the polymer chains form intermolecular hydrogen bonds with water molecules, causing the polymer chains to adopt an elongated configuration. The humidity-responsive switch is opened, promoting the rapid diffusion of water molecules within the film. At lower temperatures (below 31°C for the packaging material), the temperature-sensitive polymer chains (i.e., poly(N-isopropylacrylamide) polymer chains) form hydrogen bonds with water. The polymer chains of poly(N-isopropylacrylamide) are in an extended state, the temperature-responsive switch is closed, the pores are small, and water molecules are prevented from diffusing into the membrane. At higher temperatures (above 31°C for the packaging material), the temperature-sensitive polymer chains form intramolecular or intermolecular hydrogen bonds, the polymer chains contract, the temperature-responsive switch is opened, the pores become larger, and water molecules diffuse into the membrane. By combining different states of the humidity and temperature switches, four scenarios are obtained: low humidity and low temperature (temperature below 31°C, humidity below 60%), low humidity and high temperature (temperature below 31°C, humidity above 60%), high humidity and low temperature (temperature above 31°C, humidity below 60%), and high humidity and high temperature (temperature above 31°C, humidity above 60%). At low temperature and low humidity, both temperature and humidity response switches are closed, providing a moisturizing effect. At low temperature and high humidity, the temperature response switch is closed, while the humidity response switch is open, allowing water vapor to permeate through the packaging material. At high temperature and low humidity, the temperature response switch is open, while the humidity response switch is closed. Under high temperature and high humidity conditions, both temperature and humidity switches are open, allowing water vapor to quickly permeate the packaging material, thus regulating humidity. Therefore, when this dual-response smart film is used as packaging material, it can control the opening and closing of the switches in response to humidity and temperature, thereby regulating the internal humidity to above 60%. Verification has shown that when this smart humidity-regulating film is applied to fruit and vegetable preservation materials, it can control the internal humidity of the packaging material to 80-85%, suitable for strawberry preservation.

[0030] Beneficial technical effects of the present invention:

[0031] (1) The intelligent humidity-regulating film prepared by this invention achieves humidity control through dual temperature and humidity responses. The humidity response switch and temperature response switch open / close according to external changes, intelligently realizing the passage and blockage of water molecules inside the material, effectively controlling and adjusting the internal humidity of the packaging material, and solving the problem of single response in current humidity-regulating materials. The intelligent humidity-regulating film manufacturing process provided by this invention is mature and feasible, and has high application value in the field of packaging material technology in the future.

[0032] (2) By adding temperature-responsive polymers, the present invention enables the film to respond to external temperature stimuli, thereby achieving temperature-controlled humidity regulation.

[0033] (3) The temperature-humidity dual-response intelligent humidity control film prepared by the method of the present invention contains only C, H, O and N elements and is non-toxic.

[0034] (4) The temperature-humidity dual-response intelligent humidity-regulating film prepared by the method of the present invention has excellent preservation performance as a fruit and vegetable preservation material; the antibacterial substance loaded is tea polyphenol, which is extracted from tea leaves, has good biocompatibility, and will not produce toxic side effects on the human body.

[0035] (5) The method described in this invention for preparing a temperature-humidity dual-response intelligent humidity-regulating film is simple and combines temperature response switch and humidity response switch, enabling more intelligent regulation of the internal humidity of the material, which is of great significance in practical applications and scientific research.

[0036] (6) The temperature-humidity dual-response intelligent humidity-regulating film prepared by the method of the present invention, after being loaded with antibacterial substances, has both temperature and humidity regulation capabilities and antibacterial capabilities. The two interact with each other to achieve synergistic preservation effects in indoor and outdoor environments, high and low temperatures, and high and low humidity, effectively extending the storage time of fruits and vegetables. Attached Figure Description

[0037] Figure 1 Scanning electron microscope image of the microscopic surface morphology of the temperature-humidity dual-response smart humidity-regulating film prepared for this invention;

[0038] Figure 2 This is a schematic diagram illustrating the humidity response capability of the intelligent humidity-regulating film prepared in an embodiment of the present invention.

[0039] Figure 3 This is a schematic diagram illustrating the temperature response capability of the intelligent humidity-regulating film prepared in an embodiment of the present invention;

[0040] Figure 4 This is a schematic diagram illustrating the cyclic stability of the intelligent humidity-regulating film prepared in an embodiment of the present invention;

[0041] Figure 5This refers to the antibacterial properties of the intelligent humidity-regulating film prepared in this embodiment of the invention after being loaded with the antibacterial substance tea polyphenols;

[0042] Figure 6 This is a graph showing the changes in strawberry quality in different experimental groups after the intelligent humidity-regulating film prepared in this embodiment of the invention was loaded with antibacterial substance tea polyphenols and then subjected to a room temperature preservation experiment.

[0043] Figure 7 This is a diagram showing the changes in strawberry firmness in different experimental groups after the intelligent humidity-regulating film prepared in this embodiment of the invention is loaded with antibacterial substance tea polyphenols and then subjected to a room temperature preservation experiment.

[0044] Figure 8 The smart humidity-regulating film prepared in this embodiment of the invention is loaded with antibacterial substance tea polyphenols and then subjected to a room temperature preservation experiment. The appearance of strawberries in different experimental groups is shown in the figure.

[0045] Figure 9 This is a graph showing the changes in strawberry quality in different experimental groups after the intelligent humidity-regulating film prepared in this embodiment of the invention was loaded with antibacterial substance tea polyphenols and subjected to a high-temperature preservation experiment.

[0046] Figure 10 This is a high-temperature preservation experiment conducted on the intelligent humidity-regulating film prepared in this embodiment of the invention after loading antibacterial substance tea polyphenols. The graph shows the change in strawberry hardness in different experimental groups.

[0047] Figure 11 The intelligent humidity-regulating film prepared in this embodiment of the invention is loaded with antibacterial substance tea polyphenols and subjected to a high freshness preservation experiment. The appearance of strawberries in different experimental groups is shown in the figure.

[0048] Figure 12 This is a graph showing the humidity changes in different experimental groups at low temperatures for the intelligent humidity-regulating film prepared in this embodiment of the invention.

[0049] Figure 13 This is a graph showing the humidity changes in different experimental groups of the intelligent humidity-regulating film prepared in the embodiments of the present invention at high temperatures. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0051] Conversely, this invention encompasses any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the invention as defined in the claims. Furthermore, to provide a better understanding of the invention, certain specific details are described in detail below. However, those skilled in the art will fully understand the invention even without these detailed descriptions.

[0052] Example 1:

[0053] A method for preparing a smart humidity-regulating film with dual temperature and humidity responses, the method comprising the following steps:

[0054] (1) A temperature-responsive polymer is added during the synthesis of humidity-responsive polyurethane to obtain a polymer solution in which the temperature-responsive polymer and humidity-responsive polyurethane are mixed:

[0055] (1.1) Weigh 2g of 2,6-dipyridine methanol and dissolve it in 10ml of N,N-dimethylformamide at 45℃ to obtain a clear solution. Add 3.5g of hexamethylene diisocyanate dropwise to the reaction system under constant temperature water bath stirring. React at 45℃ for 1h.

[0056] (1.2) Mix 1.8g hexamethylene diisocyanate and 0.9g 1,4-butanediol in 10ml N,N-dimethylformamide to obtain a mixed solution. Add the mixed solution to the reaction system of step (1.1) and keep it warm in a water bath at 45-55℃.

[0057] (1.3) Dissolve 0.3g PNIPAM in 2ml N,N-dimethylformamide and stir to obtain a clear solution of poly(N-isopropylacrylamide), which is the PNIPAM solution;

[0058] (1.4) The PNIPAM solution obtained in step (1.3) is added to the reaction system in step (1.2) and placed at 45°C for 6 hours to obtain a polymer solution in which temperature-responsive polymer and humidity-responsive polyurethane are mixed.

[0059] (2) The polymer solution obtained in step (1) was deposited using solution casting to prepare a 20 μm thick intelligent humidity-regulating film with dual temperature and humidity response. The microstructure is as follows: Figure 1 As shown.

[0060] The temperature-humidity dual-response intelligent humidity-regulating film prepared in this embodiment is applied to the field of fruit and vegetable preservation, and tea polyphenols at a concentration of 1g / L are sprayed on the inside of the packaging material for antibacterial purposes.

[0061] Example 2:

[0062] A method for preparing a smart humidity-regulating film with dual temperature and humidity responses, the method comprising the following steps:

[0063] (1) A temperature-responsive polymer is added during the synthesis of humidity-responsive polyurethane to obtain a polymer solution in which the temperature-responsive polymer and humidity-responsive polyurethane are mixed:

[0064] (1.1) Weigh 2g of 2,6-dipyridine methanol and dissolve it in 10ml of N,N-dimethylformamide at 45℃ to obtain a clear solution. Add 3.5g of hexamethylene diisocyanate dropwise to the reaction system under constant temperature water bath stirring. React at 45℃ for 1h.

[0065] (1.2) Mix 1.8g hexamethylene diisocyanate and 0.9g 1,4-butanediol in 10ml N,N-dimethylformamide to obtain a mixed solution. Add the mixed solution to the reaction system of step (1.1) and keep it warm in a water bath at 45-55℃.

[0066] (1.3) Dissolve 0.3g PNIPAM in 2ml N,N-dimethylformamide and stir to obtain a clear solution of poly(N-isopropylacrylamide), which is the PNIPAM solution;

[0067] (1.4) The PNIPAM solution obtained in step (1.3) is added to the reaction system in step (1.2) and placed at 45°C for 6 hours to obtain a polymer solution in which temperature-responsive polymer and humidity-responsive polyurethane are mixed.

[0068] (2) The polymer solution obtained in step (1) is deposited by solution casting to prepare a smart humidity control film with a thickness of 30 μm that responds to both temperature and humidity.

[0069] Example 3:

[0070] A method for preparing a smart humidity-regulating film with dual temperature and humidity responses, the method comprising the following steps:

[0071] Weigh 2g of 2,6-dipyridinemethanol and dissolve it in 10ml of N,N-dimethylformamide at 45℃ to obtain a clear solution. Add 3.5g of hexamethylene diisocyanate dropwise to the reaction system under stirring in a constant temperature water bath and react at 45℃ for 1h. Then, mix 1.7g of hexamethylene diisocyanate and 0.9g of 1,4-butanediol in 10ml of N,N-dimethylformamide and add it to the reaction system. Dissolve 0.3g of PNIPAM in 2ml of N,N-dimethylformamide and add it to the reaction system. Place the system at 45℃ and react for 6h.

[0072] The prepared polymer solution was used to prepare a 40 μm thick smart humidity-regulating film with dual temperature and humidity response by solution casting.

[0073] Example 4:

[0074] A method for preparing a smart humidity-regulating film with dual temperature and humidity responses, the method comprising the following steps:

[0075] Weigh 2g of 2,6-dipyridinemethanol and dissolve it in 10ml of N,N-dimethylformamide at 45℃ to obtain a clear solution. Add 3.5g of hexamethylene diisocyanate dropwise to the reaction system with stirring in a constant temperature water bath. React at 45℃ for 1h. Then, mix 1.7g of hexamethylene diisocyanate and 0.9g of 1,4-butanediol in 10ml of N,N-dimethylformamide and add it to the reaction system. Dissolve 0.3g of PNIPAM in 2ml of N,N-dimethylformamide and add it to the reaction system. Place the system at 45℃ and react for 6h.

[0076] The prepared polymer solution was used to prepare a 50 μm thick smart humidity-regulating film with dual temperature and humidity response by solution casting.

[0077] Example 5:

[0078] A method for preparing a smart humidity-regulating film with dual temperature and humidity responses, the method comprising the following steps:

[0079] Weigh 2-3 g of 2,6-dipyridinemethanol and dissolve it in 10 ml of N,N-dimethylformamide at 45 °C to obtain a clear solution. Add 3.5 g of hexamethylene diisocyanate dropwise to the reaction system with stirring in a constant temperature water bath. React at 45 °C for 1 h. Then, mix 1.8 g of hexamethylene diisocyanate and 0.9 g of 1,4-butanediol in 10 ml of N,N-dimethylformamide and add it to the reaction system. Dissolve 0.3 g of PNIPAM in 2 ml of N,N-dimethylformamide and add it to the reaction system. Place the system at 45 °C and react for 6 h.

[0080] The prepared polymer solution was used to prepare a 50 μm thick smart humidity-regulating film with dual temperature and humidity response by solution casting.

[0081] The humidity response capabilities of the temperature-humidity dual-response smart humidity-regulating film and the PE food preservation film were compared by weighing method, specifically in terms of water vapor transmission rate performance (including the control group and the temperature-humidity dual-response smart humidity-regulating film groups corresponding to Examples 1-4). The results are as follows: Figure 2 As shown, below 60%, both water vapor transmission rate and PE are low. Above 60%, water vapor transmission rate changes abruptly. This indicates that the intelligent humidity control film with dual temperature and humidity response has excellent humidity response performance, and the 20μm thick film has even better humidity control performance.

[0082] The temperature response capabilities of the temperature-humidity dual-response smart humidity-regulating film and PE food preservation film were compared using a weighing method, specifically in terms of water vapor transmission rate performance (including the control group and the temperature-humidity dual-response smart humidity-regulating film groups corresponding to Examples 1-4). The results are as follows: Figure 3As shown, below 31℃, both water vapor transmission rate and PE are low. Above 31℃, water vapor transmission rate changes abruptly. This indicates that the intelligent humidity control film with dual temperature and humidity response has excellent temperature response performance, and the 20μm thick film has a more obvious temperature response and better humidity control performance.

[0083] The cycling stability of the temperature-humidity dual-response smart humidity-regulating film was compared by weighing method, such as... Figure 4 As shown, the packaging material exhibits good cyclic stability under varying humidity and temperature conditions, demonstrating that the intelligent humidity-regulating film material with dual temperature and humidity response is stable and reusable.

[0084] Further research was conducted on the antibacterial effects of the temperature-humidity dual-response intelligent humidity-regulating film on *Escherichia coli* and *Staphylococcus aureus* after loading with the antibacterial substance tea polyphenols. Figure 5 The intelligent composite film shown exhibits excellent antibacterial effects against both types of bacteria.

[0085] The following experiment used fresh strawberries as the test object. The intelligent humidity-regulating film with temperature-humidity dual response prepared in Example 1 was used as the packaging material to preserve the strawberries as one group, and another group of strawberries packaged with commercially available PE preservation film was used as the control group.

[0086] After packaging, the strawberries were placed in the same room temperature environment. The next day, the strawberries were removed and weighed and their firmness measured. The experimental data were recorded. After the test, the strawberries were returned to their corresponding packaging material. This experiment was repeated for 7 consecutive days, and the experimental data were recorded. A curve graph showing the change in strawberry weight and firmness over time was plotted. Figure 6 , 7 As shown. Take photos to record the appearance of the strawberries on day 1 and day 7, as shown. Figure 8 As shown.

[0087] After packaging, the strawberries were placed in the same high-temperature environment. The next day, the strawberries were removed and weighed and their firmness measured. The experimental data were recorded. After testing, the strawberries were returned to their corresponding packaging materials. This experiment was repeated for four consecutive days, and the experimental data were recorded. A graph showing the change in strawberry weight and firmness over time was plotted. Figure 9 , 10 As shown. Take photos to record the appearance of the strawberries on day 1 and day 4, as shown. Figure 11 As shown.

[0088] While the preservation experiment was being conducted, the internal moisture of the packaging material was recorded, and humidity change curves were plotted for the packaging material at room temperature and high temperature. Figure 12 , 13 As shown.

[0089] Depend on Figure 6It can be seen that under room temperature preservation conditions, the weight of strawberries in both groups of preservation materials decreased. However, the strawberries packaged with the temperature-humidity dual-response intelligent humidity-regulating film lost less weight than the strawberries packaged with PE preservation film. This indicates that the temperature-humidity dual-response intelligent humidity-regulating film has a better preservation effect on strawberries under room temperature conditions.

[0090] Depend on Figure 7 It can be seen that under room temperature preservation conditions, the firmness of strawberries in both groups of preservation materials decreased. However, the strawberries packaged with the temperature-humidity dual-response intelligent humidity-regulating film showed less decrease in firmness than the strawberries packaged with PE preservation film. This indicates that the temperature-humidity dual-response intelligent humidity-regulating film has a better preservation effect on strawberries under room temperature conditions.

[0091] Depend on Figure 8 It can be seen that under room temperature preservation conditions, the strawberries in the PE preservation film group were severely rotten by the 7th day, while the strawberries packaged with the temperature-humidity dual-response intelligent humidity control film remained relatively fresh by the 7th day. Therefore, it is proven that the temperature-humidity dual-response intelligent humidity control film has a good effect on the preservation of strawberries at room temperature.

[0092] Depend on Figure 9 It can be seen that under high-temperature preservation conditions, the weight of strawberries in both groups of preservation materials decreased. However, the strawberries packaged with the temperature-humidity dual-response intelligent humidity-regulating film experienced less weight loss than those packaged with PE preservation film. This indicates that the temperature-humidity dual-response intelligent humidity-regulating film has a better preservation effect on strawberries under high-temperature conditions.

[0093] Depend on Figure 10 It can be seen that under high-temperature preservation conditions, the firmness of strawberries in both groups of preservation materials decreased. However, the strawberries packaged with the temperature-humidity dual-response intelligent humidity-regulating film showed less decrease in firmness than the strawberries packaged with PE preservation film. This indicates that the temperature-humidity dual-response intelligent humidity-regulating film has a better preservation effect on strawberries under high-temperature conditions.

[0094] Depend on Figure 11 It can be seen that under high-temperature preservation conditions, the strawberries in the PE preservation film group were already severely rotten by day 3, while the strawberries packaged with the temperature-humidity dual-response intelligent humidity control film remained relatively fresh on day 3. Therefore, it is proven that the temperature-humidity dual-response intelligent humidity control film has a significant effect on the preservation of strawberries at high temperatures.

[0095] Depend on Figure 12 and 13It can be seen that the humidity inside the packaging of the temperature-humidity dual-response intelligent humidity-regulating film is significantly lower than that of the PE preservation film. Specifically, the temperature-humidity dual-response intelligent humidity-regulating film can control the humidity inside the packaging material at 80%-85%, while the humidity inside the PE preservation film packaging is maintained at around 95%, with excessively high humidity accelerating the spoilage of strawberries. This proves that the temperature-humidity dual-response intelligent humidity-regulating film has a better preservation effect on strawberries.

[0096] The above experiments demonstrate that the intelligent humidity-regulating film with dual temperature and humidity response prepared using this invention has a significant preservation effect and can effectively extend the storage period of fruits and vegetables.

[0097] As can be seen from the above embodiments, the present invention can achieve humidity and temperature dual-response humidity regulation. Temperature-controlled humidity regulation increases the controllability of humidity regulation. The intelligent humidity regulating film with temperature and humidity dual response prepared by the present invention can be widely used in the fields of building indoor humidity regulation, protection of library collections and cultural relics, food and medicine storage, and fruit and vegetable preservation.

[0098] This invention discloses a smart humidity-regulating film with dual temperature and humidity responses, its preparation method, and its application, belonging to the field of packaging materials technology. The temperature and humidity response "switches" of the packaging material originate from a temperature-responsive system: poly(N-isopropylacrylamide), and a humidity-responsive system: humidity-responsive polyurethane, respectively. This invention is carried out through a condensation polymerization reaction. First, a humidity-responsive polyurethane prepolymer is generated through an addition polymerization reaction, and then the temperature-sensitive polymer poly(N-isopropylacrylamide) (PNIPAM) is added. The humidity-responsive polyurethane prepolymer in the system condenses to form a humidity-responsive polyurethane. PNIPAM and humidity-responsive polyurethane are mixed in solution. The temperature-humidity responsive polymer solution is then cast into a film using a solution casting method, successfully preparing a smart film with dual temperature and humidity responses. The temperature-humidity responsive smart film prepared by this invention can regulate the internal humidity of the material by dual temperature and humidity "switches"; the humidity response threshold is 60%, and the temperature response threshold is 31℃. Loading antibacterial substances onto the material surface for application in the field of fruit and vegetable preservation gives the film material both humidity-regulating and antibacterial properties; the film loaded with antibacterial substances exhibits good preservation and anti-corrosion effects. The manufacturing process of this temperature-humidity dual-response intelligent humidity-regulating film is mature and feasible, and it has high application value in the field of packaging materials technology in the future.

[0099] The specific embodiments described above are only used to illustrate the spirit of the present invention. The scope of protection of the present invention is not limited thereto. Modifications made by those skilled in the art under the guidance of the present invention and within the scope of the spirit of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing a smart humidity-regulating film with dual temperature and humidity responses, characterized in that, The method includes the following steps: (1) A temperature-responsive polymer is added during the synthesis of humidity-responsive polyurethane to obtain a polymer solution in which the temperature-responsive polymer and humidity-responsive polyurethane are mixed. (2) The polymer solution obtained in step (1) is deposited by solution casting to prepare a temperature-humidity dual-response smart humidity control film; the thickness of the prepared temperature-humidity dual-response humidity control film is 20-50 μm. (3) Load antibacterial substances onto the surface of the intelligent humidity-regulating film obtained in step (2) to obtain an intelligent humidity-regulating film with antibacterial, temperature-regulating and humidity-regulating properties; the loading method is: spray a tea polyphenol solution with a concentration of (1-4) g / L onto the inner side of the intelligent humidity-regulating film for antibacterial purposes. The intelligent humidity-regulating film has a humidity response threshold of 60% and a temperature response threshold of 31°C, and is used as a fruit and vegetable preservation material. The temperature-responsive polymer used in step (1) is poly(N-isopropylacrylamide); Step (1) specifically includes: (1.1) Dissolve 2,6-pyridinediethanol in a solvent and stir to obtain a clear solution. Add hexamethylene diisocyanate dropwise under constant temperature of 45-55℃ and stir for 1-2 hours. The mass ratio of 2,6-pyridinediethanol to hexamethylene diisocyanate is (4-6):

7. (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 warm in a water bath at 45-55℃. (1.3) Dissolve poly(N-isopropylacrylamide) in a solvent and stir to obtain a clear solution of poly(N-isopropylacrylamide), which is the PNIPAM solution; (1.4) Add the PNIPAM solution obtained in step (1.3) to the reaction system in step (1.2) and react for 6-8 hours to obtain a polymer solution in which temperature-responsive polymer and humidity-responsive polyurethane are mixed. In step (1.1), the mass ratio of 2,6-pyridinediethanol to 1,4-butanediol in step (1.2) is (20-30):9; in the reaction system of step (1.4), the mass ratio of poly(N-isopropylacrylamide) to the total mass of hexamethylene diisocyanate, 2,6-pyridinediethanol, and 1,4-butanediol is 3:(82-92).

2. The method for preparing the intelligent humidity-regulating film with dual temperature and humidity response according to claim 1, characterized in that, In steps (1.1), (1.2), and (1.3), the solvent used is N,N-dimethylformamide. In step (1.1), the ratio of 2,6-pyridinediethanol to solvent is (2-3):10, in g / mL. In step (1.2), the mass ratio of hexamethylene diisocyanate to 1,4-butanediol is 2:1; the material-to-liquid ratio of hexamethylene diisocyanate to solvent is 9:50, in g / mL. In step (1.3), the ratio of poly(N-isopropylacrylamide) to solvent is 3:20, in g / mL.

3. The method for preparing the intelligent humidity-regulating film with dual temperature and humidity response according to claim 1, characterized in that, Step (2) specifically involves: using a solution casting method, the polymer solution obtained in step (1) is spread evenly on a glass plate using a film-laying machine, and placed in an oven at 40-60℃ for 15-24 hours to obtain a smart humidity-regulating film with dual temperature and humidity response.

4. A smart humidity-regulating film with dual temperature and humidity responses, prepared by the preparation method according to any one of claims 1-3, characterized in that, The intelligent humidity-regulating film regulates the internal humidity of the packaging material through dual responses of temperature and humidity; the humidity response threshold of the intelligent humidity-regulating film is 60%, and the temperature response threshold is 31°C.

5. An application of the intelligent humidity-regulating film with dual temperature and humidity response as described in claim 4, characterized in that, The intelligent humidity-regulating film is applied in the field of food preservation.

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