Intelligent humidity-adjusting film with temperature and humidity double response as well as preparation method and application of intelligent humidity-adjusting film

Abstract

The invention belongs to the technical field of packaging materials, and relates to an intelligent humidity-adjusting film with temperature and humidity double response as well as a preparation method and application thereof. A temperature response system of the packaging material is from poly (N-isopropylacrylamide), and a humidity response system is from humidity response polyurethane. The intelligent humidity-adjusting film with temperature and humidity double responses is successfully prepared through condensation polymerization reaction and film laying by a solution casting method. According to the prepared intelligent humidity adjusting film, the internal humidity of the material can be adjusted through temperature and humidity double'switches'; the humidity response threshold value is 60%, and the temperature response threshold value is 31 DEG C. Antibacterial substances are loaded on the surface of the material, and the film material is applied to the field of fruit and vegetable preservation, so that the film material has humidifying and antibacterial properties; the film loaded with the antibacterial substances shows good fresh-keeping and preservative effects. The temperature-humidity double-response intelligent humidity adjusting film is mature and feasible in manufacturing process, and has very high application value in the technical field of packaging materials in the future.

Description

Technical Field

[0001] The present invention belongs to the technical field of packaging materials, and in particular relates to an intelligent humidity-regulating film with dual responses to temperature and humidity, and a preparation method and application thereof. Background Art

[0002] Every year, 200 million tons of fruits and vegetables are lost, with economic losses reaching 75 billion yuan. Eating rotten fruits and vegetables can easily lead to food poisoning, and even cause coma and endanger the life of the eater; efficient and low-cost post-harvest preservation of fruits and vegetables has always been one of the problems that need to be solved in the food industry.

[0003] The phenomenon of fruit and vegetable sweating refers to the phenomenon of condensation of water droplets on the inner surface of the packaging material during the storage, transportation and sales of fruits and vegetables after harvesting. This is mainly because fruits and vegetables are still fresh "living organisms" after picking, and their respiration and transpiration will continue to produce moisture. When traditional plastic wrap materials are used for storage, the air permeability and moisture permeability are poor. Under conditions of high humidity and temperature difference, it will cause fogging and condensation inside the packaging. When the humidity is too high, it is easy to breed bacteria. Water droplets dripping on the surface of fruits and vegetables will accelerate the decay of the fruits and vegetables, seriously shortening the shelf life of fruits and vegetables.

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

[0005] The patent with application number 202311538918.7 discloses an intelligent composite film, preparation method and application with both humidity control and antibacterial capabilities. Although the intelligent composite film disclosed in the patent can achieve humidity control and antibacterial, the intelligent composite film cannot adjust the humidity in response to the ambient temperature. The respiration and transpiration of the fruit itself are greatly affected by the ambient temperature. When the temperature is high, the respiration and transpiration of the fruits and vegetables themselves will be enhanced, resulting in excessive humidity inside the packaging material. Therefore, under high temperature conditions, the humidity inside the packaging material will also rise sharply. Therefore, the response of adjusting the humidity inside the package by humidity response alone is single, so the method of the present invention introduces dual-response humidity regulation in a complex environment, so that the packaging material can achieve multiple stimulus responses to adjust the humidity. Summary of the invention

[0006] In view of the above technical problems, the present invention provides a smart humidity-regulating film with dual response to temperature and humidity, as well as a preparation method and application. The smart film provided by the present invention has dual stimulus response to temperature and humidity to regulate the humidity inside the package. First, it realizes switching by responding to the humidity change of the external environment through its internal hydrogen bonds, and second, it realizes switching by responding to the temperature change through its internal thermosensitive polymer chain, thereby realizing the passage and blocking of water vapor molecules inside the package, thereby effectively regulating the humidity inside the package.

[0007] The technical solution adopted by the present invention is:

[0008] A method for preparing an intelligent humidity-controlling film having dual responses to temperature and humidity, the method comprising the following steps:

[0009] (1) adding a temperature-responsive polymer during the synthesis of the humidity-responsive polyurethane to obtain a polymer solution in which the temperature-responsive polymer and the humidity-responsive polyurethane are mixed with each other;

[0010] (2) The polymer solution obtained in step (1) is cast into a film by a solution casting method to obtain a temperature-humidity dual-responsive intelligent humidity-regulating film.

[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-pyridine dimethanol in a solvent and stir to obtain a clear solution. Add hexamethylene diisocyanate dropwise in a water bath at a constant temperature of 45-55°C while stirring. Keep stirring at the constant temperature for 1-2 hours.

[0014] (1.2) mixing hexamethylene diisocyanate and 1,4-butanediol in a solvent in a certain proportion to obtain a mixed solution, adding the mixed solution to the reaction system of step (1.1), and keeping the mixture in a water bath at 45-55° C.;

[0015] (1.3) dissolving poly(N-isopropylacrylamide) in a solvent, and stirring to obtain a clear solution of poly(N-isopropylacrylamide), i.e., obtaining a PNIPAM solution;

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

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

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

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

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

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

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

[0023] Furthermore, step (2) is specifically as follows: by solution casting, the polymer solution obtained in step (1) is spread on a glass plate by a film laying machine, and placed in a 40-60°C oven for 15-24 hours to obtain a temperature-humidity dual-responsive intelligent humidity-regulating film.

[0024] Furthermore, the temperature-humidity dual-responsive humidity-regulating film prepared in step (2) has a thickness of 20-50 μm.

[0025] Furthermore, the method further comprises step (3): loading the surface of the smart humidity-controlling film obtained in step (2) with an antibacterial substance to obtain a smart humidity-controlling film having antibacterial properties, temperature-controlling properties and humidity-controlling properties;

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

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

[0028] The invention discloses an application of a temperature and humidity dual-responsive intelligent humidity-controlling film having both humidity-controlling and antibacterial capabilities, and applies the intelligent humidity-controlling film in the field of food preservation.

[0029] The technical principle of the present invention is as follows: the humidity control function of the temperature and humidity dual-responsive intelligent humidity control film provided by the present invention is mainly controlled by two "switches" of temperature and humidity. When the humidity is low (the humidity inside the packaging material is lower than 60%), the polymer chains of the humidity-responsive polyurethane can form intramolecular hydrogen bonds, so that the polymer chains are closely stacked together, and the humidity response switch is closed, which hinders the passage of water molecules; when the humidity is high (the humidity inside the packaging material is greater than 60%), water molecules participate in the hydrogen bond competition in the humidity response system, and the intramolecular hydrogen bonds between the polymer chains form intermolecular hydrogen bonds with water molecules, so that the polymer chains are in an elongated configuration, and the humidity response switch is turned on, which promotes the rapid diffusion of water molecules in the film. When the temperature is low (the temperature of the packaging material is lower than 31°C), the thermosensitive polymer chain (i.e., poly(N-isopropylacrylamide) polymer chain) forms hydrogen bonds with water, the polymer chain of poly(N-isopropylacrylamide) is in an extended state, the temperature response switch is closed, the pores are smaller, and water molecules are prevented from diffusing in the membrane; when the temperature is high (the temperature of the packaging material is higher than 31°C), the thermosensitive polymer chain forms intramolecular hydrogen bonds or intermolecular hydrogen bonds, the polymer chain shrinks, the temperature response switch is opened, the pores become larger, and the diffusion of water molecules in the membrane is promoted; by combining the different states of the humidity and temperature switches, four conditions are obtained: low humidity and low temperature (temperature lower than 31°C, humidity lower than 60%), low humidity and high temperature (temperature lower than 31°C, humidity higher than 60%), high humidity and low temperature (temperature higher than 31°C, humidity lower than 60%), and high humidity and high temperature (temperature higher than 31°C, humidity higher than 60%). At low temperature and low humidity, the temperature-humidity response switch is closed, which plays a moisturizing role; at low temperature and high humidity, the temperature response switch is closed, the humidity response switch is open, and water vapor can pass through the packaging material for moisture permeation; when the temperature is high and the humidity is low, the temperature response switch is open, and the humidity response switch is closed; when the temperature is high and the humidity is high, the temperature-humidity dual switch is open, and water vapor can quickly pass through the packaging material to play a humidity control role; when the dual-response smart film is used as a packaging material, it can respond to humidity and temperature to control the opening and closing of the switch, thereby regulating the internal humidity to more than 60%. It has been verified that when the smart humidity-regulating film is applied to fruit and vegetable preservation materials, the humidity inside the packaging material can be controlled at 80-85%, which is suitable for the preservation of strawberries.

[0030] Beneficial technical effects of the present invention:

[0031] (1) The temperature-humidity dual-response intelligent humidity-controlling film prepared by the present invention realizes humidity control through dual-response of temperature and humidity. The humidity-response switch and the temperature-response switch are turned on / off according to external changes, intelligently realizing the passage and blocking of water molecules inside the material, effectively controlling and adjusting the humidity inside the packaging material, and solving the problem of single response of humidity-controlling materials at present. The manufacturing process of the intelligent humidity-controlling film provided by the present invention is mature and feasible, and has high application value in the field of packaging material technology in the future.

[0032] (2) The present invention adds a temperature-responsive polymer so that the film can respond to external temperature stimuli, thereby achieving temperature-controllable humidity control.

[0033] (3) The temperature-humidity dual-responsive intelligent humidity-regulating 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-responsive intelligent humidity-regulating film prepared by the method of the present invention is used as a fruit and vegetable preservation material with excellent preservation performance; the loaded antibacterial substance is tea polyphenols, which is extracted from tea leaves and has good biocompatibility and will not produce toxic side effects on the human body.

[0035] (5) The preparation method of the temperature-humidity dual-response intelligent humidity-regulating film prepared by the method described in the present invention is simple, and has both a temperature response switch and a humidity response switch, and can more intelligently regulate the humidity inside the material, which is of great significance in practical applications and scientific research.

[0036] (6) After the temperature-humidity dual-responsive intelligent humidity-regulating film prepared by the method of the present invention is loaded with antibacterial substances, it has both temperature and humidity regulation capabilities and antibacterial capabilities. The two interact with each other to achieve a synergistic preservation effect indoors and outdoors, at high and low temperatures, and at high and low humidity, effectively extending the storage time of fruits and vegetables. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a scanning electron microscope photo of the microscopic surface morphology of the temperature-humidity dual-responsive intelligent humidity-regulating film prepared by the present invention;

[0038] Figure 2 A schematic diagram of the humidity response capability of the intelligent humidity-controlling film prepared in an embodiment of the present invention;

[0039] Figure 3 A schematic diagram of the temperature response capability of the intelligent humidity-controlling film prepared in an embodiment of the present invention;

[0040] Figure 4 A schematic diagram of the cyclic stability of the intelligent humidity-controlling film prepared in an embodiment of the present invention;

[0041] Figure 5The antibacterial performance of the intelligent humidity-control film prepared in the embodiment of the present invention after loading the antibacterial substance tea polyphenols;

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

[0043] Figure 7 This is a diagram showing the hardness changes of strawberries in different experimental groups after the intelligent humidity-control film prepared in the embodiment of the present invention is loaded with the antibacterial substance tea polyphenols and subjected to a room temperature preservation experiment;

[0044] Figure 8 This is a room temperature preservation experiment after the intelligent humidity-control film prepared in the embodiment of the present invention is loaded with the antibacterial substance tea polyphenols, and the appearance of strawberries in different experimental groups;

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

[0046] Fig.10 This is a diagram showing the hardness changes of strawberries in different experimental groups after the intelligent humidity-control film prepared in the embodiment of the present invention was loaded with the antibacterial substance tea polyphenols and subjected to a high-temperature preservation experiment;

[0047] Fig.11 This is a high freshness preservation experiment after the intelligent humidity-control film prepared in the embodiment of the present invention is loaded with the antibacterial substance tea polyphenols, and the appearance of strawberries in different experimental groups;

[0048] Fig.12 is a diagram showing humidity changes in different experimental groups at low temperatures for the intelligent humidity-controlling film prepared in an embodiment of the present invention;

[0049] Fig.13 3 is a diagram showing humidity changes in different experimental groups at high temperatures for the intelligent humidity-regulating film prepared in an embodiment of the present invention. DETAILED DESCRIPTION

[0050] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0051] On the contrary, the present invention covers any substitution, modification, equivalent method and scheme made on the essence and scope of the present invention as defined by the claims. Further, in order to make the public have a better understanding of the present invention, some specific details are described in detail in the detailed description of the present invention below. Those skilled in the art can fully understand the present invention without the description of these details.

[0052] Embodiment 1:

[0053] A method for preparing an intelligent humidity-controlling film with dual responses to temperature and humidity, the method comprising the following steps:

[0054] (1) Adding a temperature-responsive polymer during the synthesis of a humidity-responsive polyurethane to obtain a polymer solution in which the temperature-responsive polymer and the humidity-responsive polyurethane are mixed with each other:

[0055] (1.1) Weigh 2 g of 2,6-bipyridinemethanol 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 under stirring in a constant temperature water bath. React at 45°C for 1 h.

[0056] (1.2) 1.8 g of hexamethylene diisocyanate and 0.9 g of 1,4-butanediol were mixed in 10 ml of N,N-dimethylformamide to obtain a mixed solution, and the mixed solution was added to the reaction system of step (1.1); the mixture was placed in a water bath at 45-55° C. for insulation;

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

[0058] (1.4) Add the PNIPAM solution obtained in step (1.3) to the reaction system of step (1.2), place it at 45° C., and react for 6 hours to obtain a polymer solution in which the temperature-responsive polymer and the humidity-responsive polyurethane are mixed.

[0059] (2) The polymer solution obtained in step (1) is casted by a solution casting method to prepare a 20 μm thick temperature-humidity dual-responsive intelligent humidity-regulating film, the microscopic morphology of which is as follows: Figure 1 shown.

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

[0061] Embodiment 2:

[0062] A method for preparing an intelligent humidity-controlling film with dual responses to temperature and humidity, the method comprising the following steps:

[0063] (1) Adding a temperature-responsive polymer during the synthesis of a humidity-responsive polyurethane to obtain a polymer solution in which the temperature-responsive polymer and the humidity-responsive polyurethane are mixed with each other:

[0064] (1.1) Weigh 2 g of 2,6-bipyridinemethanol 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 under stirring in a constant temperature water bath. React at 45°C for 1 h.

[0065] (1.2) 1.8 g of hexamethylene diisocyanate and 0.9 g of 1,4-butanediol were mixed in 10 ml of N,N-dimethylformamide to obtain a mixed solution, and the mixed solution was added to the reaction system of step (1.1); the mixture was placed in a water bath at 45-55° C. for insulation;

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

[0067] (1.4) Add the PNIPAM solution obtained in step (1.3) to the reaction system of step (1.2), place it at 45° C., and react for 6 hours to obtain a polymer solution in which the temperature-responsive polymer and the humidity-responsive polyurethane are mixed.

[0068] (2) The polymer solution obtained in step (1) is cast into a film by a solution casting method to prepare a temperature-humidity dual-responsive intelligent humidity-regulating film with a thickness of 30 μm.

[0069] Embodiment 3:

[0070] A method for preparing an intelligent humidity-controlling film with dual responses to temperature and humidity, the method comprising the following steps:

[0071] Weigh 2 g of 2,6-bipyridinemethanol 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 under stirring in a constant temperature water bath. React at 45°C for 1 hour. Then, mix 1.7 g of hexamethylene diisocyanate and 0.9 g of 1,4-butanediol in 10 ml of N,N-dimethylformamide and add to the reaction system. Dissolve 0.3 g of PNIPAM in 2 ml of N,N-dimethylformamide and add to the reaction system. Place the system at 45°C and react for 6 hours.

[0072] The prepared polymer solution was used to prepare a 40 μm thick temperature-humidity dual-responsive smart humidity-regulating film through a solution casting method.

[0073] Embodiment 4:

[0074] A method for preparing an intelligent humidity-controlling film with dual responses to temperature and humidity, the method comprising the following steps:

[0075] Weigh 2 g of 2,6-bipyridinemethanol 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 under stirring in a constant temperature water bath. React at 45°C for 1 h. Then, mix 1.7 g of hexamethylene diisocyanate and 0.9 g of 1,4-butanediol in 10 ml of N,N-dimethylformamide and add to the reaction system. Dissolve 0.3 g of PNIPAM in 2 ml of N,N-dimethylformamide and add to the reaction system. Place the system at 45°C and react for 6 h.

[0076] The prepared polymer solution was used to prepare a 50 μm thick temperature-humidity dual-responsive smart humidity-regulating film through a solution casting method.

[0077] Embodiment 5:

[0078] A method for preparing an intelligent humidity-controlling film with dual responses to temperature and humidity, the method comprising the following steps:

[0079] Weigh 2-3 g of 2,6-bipyridinemethanol 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 under stirring in a constant temperature water bath. React at 45°C for 1 hour. 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 to the reaction system. Dissolve 0.3 g of PNIPAM in 2 ml of N,N-dimethylformamide and add to the reaction system. Place the system at 45°C and react for 6 hours.

[0080] The prepared polymer solution was used to prepare a 50 μm thick temperature-humidity dual-responsive smart humidity-regulating film through a solution casting method.

[0081] The humidity response capabilities of the temperature-humidity dual-responsive smart humidity-controlling film and the PE cling film were compared by weighing method, which was specifically reflected in the water vapor transmission rate performance (including the control group and the temperature-humidity dual-responsive smart humidity-controlling film group corresponding to Examples 1-4). The results are as follows Figure 2 As shown, below 60%, the water vapor permeability and PE are both low. Above 60%, the water vapor permeability changes suddenly. It can be seen that the temperature-humidity dual-responsive intelligent humidity-regulating film has excellent humidity response performance, and the humidity-regulating performance of the film with a thickness of 20μm is better.

[0082] The temperature response capabilities of the temperature-humidity dual-responsive smart humidity-controlling film and the PE cling film were compared by weighing method, which was specifically reflected in the water vapor transmission rate performance (including the control group and the temperature-humidity dual-responsive smart humidity-controlling film group corresponding to Examples 1-4). The results are as follows Figure 3As shown, below 31°C, the water vapor permeability and PE are both low. Above 31°C, the water vapor permeability changes suddenly. It can be seen that the temperature-humidity dual-responsive intelligent humidity-regulating film has excellent temperature response performance, and the temperature response of the 20μm thick film is more obvious, and the humidity-regulating performance is better.

[0083] The cyclic stability of the temperature-humidity dual-responsive smart humidity-regulating film was compared by weighing method. Figure 4 As shown. It can be seen that the packaging material has good cycle stability when changing different humidity and temperature, proving that the performance of the temperature-humidity dual-responsive intelligent humidity-regulating film material is stable and can be reused.

[0084] The antibacterial effect of the temperature-humidity dual-responsive smart humidity-regulating film on Escherichia coli and Staphylococcus aureus after loading the antibacterial substance tea polyphenols was further studied. Figure 5 The smart composite film shown has excellent antibacterial effect on both bacteria.

[0085] The following experiment uses fresh strawberries as test objects, and uses the humidity-regulating temperature-humidity dual-responsive intelligent humidity-regulating film prepared in Example 1 as a packaging material to preserve strawberries as one group, and another group of strawberries packaged with commercially available PE cling film as a control group.

[0086] After packaging, place the strawberries in the same room temperature environment. Take out the strawberries every other day to weigh and measure their hardness. Record the experimental data. After the test is completed, put them back into the corresponding packaging materials. Repeat the above experiment for 7 consecutive days, record the experimental data, and draw a curve chart of the change of strawberry quality and hardness over time, as shown in Figure 1. Figure 6 , 7 Take photos to record the appearance of the strawberries on the 1st and 7th days, as shown in Figure 8 shown.

[0087] After packaging the strawberries, place them in the same high temperature environment. Take out the strawberries every other day to weigh and measure their hardness. Record the experimental data. After the test is completed, put them back into the corresponding packaging materials. Repeat the above experiment for 4 consecutive days, record the experimental data, and draw a curve chart of the change of strawberry quality and hardness over time, as shown in Figure 1. Fig. 9 , 10 Take photos to record the appearance of the strawberries on the 1st and 4th days, as shown in Fig.11 shown.

[0088] While the preservation experiment is in progress, the internal humidity of the packaging material is recorded, and the humidity change curves of the packaging material at room temperature and high temperature are drawn, such as Fig.12 , 13 shown.

[0089] Depend on Figure 6It can be seen that under room temperature preservation conditions, the weight of strawberry fruits in both groups of preservation materials is decreasing, but the weight of strawberries packaged with the temperature-humidity dual-responsive intelligent humidity-regulating film is less than that of strawberries packaged with PE plastic wrap, indicating that the temperature-humidity dual-responsive intelligent humidity-regulating film has a better preservation effect on strawberries at room temperature.

[0090] Depend on Figure 7 It can be seen that under room temperature preservation conditions, the hardness of the strawberry fruits in the two groups of preservation materials is decreasing, but the hardness of the strawberries packaged with the temperature-humidity dual-responsive intelligent humidity-regulating film decreases less than that of the strawberries packaged with PE plastic wrap, indicating that the temperature-humidity dual-responsive intelligent humidity-regulating film has a better preservation effect on strawberries at room temperature.

[0091] Depend on Figure 8 It can be seen that under room temperature preservation conditions, the strawberries in the PE cling film group had severely rotted on the 7th day, while the strawberries packaged with the temperature-humidity dual-responsive intelligent humidity-regulating film remained relatively fresh on the 7th day. This proves that the temperature-humidity dual-responsive intelligent humidity-regulating film has a good effect on preserving strawberries at room temperature.

[0092] Depend on Fig. 9 It can be seen that under high-temperature preservation conditions, the weight of strawberry fruits in both groups of preservation materials is decreasing, but the weight of strawberries packaged with the temperature-humidity dual-responsive intelligent humidity-regulating film is less than that of strawberries packaged with PE plastic wrap, indicating that the temperature-humidity dual-responsive intelligent humidity-regulating film has a better preservation effect on strawberries under high temperature conditions.

[0093] Depend on Fig.10 It can be seen that under high-temperature preservation conditions, the hardness of strawberry fruits in both groups of preservation materials is decreasing, but the hardness of strawberries packaged with the temperature-humidity dual-responsive intelligent humidity-regulating film decreases less than that of strawberries packaged with PE plastic wrap, indicating that the temperature-humidity dual-responsive intelligent humidity-regulating film has a better preservation effect on strawberries under high temperature conditions.

[0094] Depend on Fig.11 It can be seen that under high-temperature preservation conditions, the strawberries in the PE cling film group had already rotted severely on the third day, while the strawberries packaged with the temperature-humidity dual-responsive intelligent humidity-regulating film remained relatively fresh on the third day. This proves that the temperature-humidity dual-responsive intelligent humidity-regulating film has a significant effect on preserving strawberries at high temperatures.

[0095] Depend on Fig.12 and 13It can be seen that the humidity inside the temperature-humidity dual-responsive intelligent humidity-control film package is significantly lower than that of the PE cling film. Among them, the temperature-humidity dual-responsive intelligent humidity-control film can control the humidity inside the packaging material at 80%-85%, while the humidity inside the PE cling film package is maintained at around 95%. Excessive humidity aggravates the rot of strawberries. This proves that the temperature-humidity dual-responsive intelligent humidity-control film has a good preservation effect on strawberries.

[0096] The above experiments can prove that the temperature-humidity dual-responsive intelligent humidity-regulating film prepared by the present invention has a significant fresh-keeping effect and can effectively extend the storage period of fruits and vegetables.

[0097] It can be concluded from the above embodiments that the present invention can realize humidity and temperature dual-responsive humidity control, and temperature humidity control increases the controllability of humidity control. The temperature-humidity dual-responsive intelligent humidity control film prepared by the present invention can be widely used in the fields of indoor humidity control in buildings, protection of library books and cultural relics, storage of food and medicine, preservation of fruits and vegetables, etc.

[0098] The present invention discloses an intelligent humidity-controlling film with dual response to temperature and humidity, a preparation method and application, and belongs to the technical field of packaging materials. The temperature and humidity response "switch" of the packaging material comes from the temperature response system: poly (N-isopropylacrylamide), and the humidity response system: humidity response polyurethane. The present invention is carried out by polycondensation reaction. First, a prepolymer of humidity-responsive polyurethane is generated by addition polymerization reaction, and then the thermosensitive polymer poly (N-isopropylacrylamide) (PNIPAM) is added. The prepolymer of humidity-responsive polyurethane in the system is polycondensed into humidity-responsive polyurethane; PNIPAM and humidity-responsive polyurethane are mixed with each other in the solution; the temperature-humidity response polymer solution is laid by solution casting method, and an intelligent film with dual response to temperature and humidity is successfully prepared. The temperature-humidity dual response intelligent film prepared by the present invention can realize the dual "switch" of temperature and humidity to adjust the internal humidity of the material; the humidity response threshold is 60%, and the temperature response threshold is 31°C. Antibacterial substances are loaded on the surface of the material for application in the field of fruit and vegetable preservation, so that the film material has both humidity control and antibacterial properties; the film loaded with antibacterial substances exhibits good preservation and antiseptic effects. The manufacturing process of the temperature-humidity dual-response intelligent humidity-regulating film is mature and feasible, and will have high application value in the field of packaging material technology in the future.

[0099] The specific implementation methods described above are only used to specifically illustrate the spirit of the present invention, and the protection scope of the present invention is not limited thereto. Under the guidance of the present invention, changes made by technicians in this field within the scope covered by the purpose of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing an intelligent humidity-controlling film with dual response to temperature and humidity, characterized in that: The method comprises the following steps: (1) adding a temperature-responsive polymer during the synthesis of the humidity-responsive polyurethane to obtain a polymer solution in which the temperature-responsive polymer and the humidity-responsive polyurethane are mixed with each other; (2) The polymer solution obtained in step (1) is cast into a film by a solution casting method to obtain a temperature-humidity dual-responsive intelligent humidity-regulating film.

2. The method for preparing the intelligent humidity-controlling film with dual response to temperature and humidity according to claim 1, characterized in that: The temperature-responsive polymer used in step (1) is poly(N-isopropylacrylamide).

3. The method for preparing the intelligent humidity-controlling film with dual response to temperature and humidity according to claim 1, characterized in that: Step (1) specifically includes: (1.1) Dissolve 2,6-pyridine dimethanol in a solvent and stir to obtain a clear solution. Add hexamethylene diisocyanate dropwise in a water bath at a constant temperature of 45-55°C while stirring. Keep stirring at the constant temperature for 1-2 hours. (1.2) mixing hexamethylene diisocyanate and 1,4-butanediol in a solvent in a certain proportion to obtain a mixed solution, adding the mixed solution to the reaction system of step (1.1), and keeping the mixture in a water bath at 45-55° C.; (1.3) dissolving poly(N-isopropylacrylamide) in a solvent and stirring to obtain a clear solution of poly(N-isopropylacrylamide), i.e., obtaining a PNIPAM solution; (1.4) Add the PNIPAM solution obtained in step (1.3) to the reaction system of step (1.2), and react for 6-8 hours to obtain a polymer solution in which the temperature-responsive polymer and the humidity-responsive polyurethane are mixed.

4. The method for preparing the intelligent humidity-controlling film with dual response to temperature and humidity according to claim 3, characterized in that: In step (1.1), step (1.2) and step (1.3), the solvent used is N,N-dimethylformamide; In step (1.1), the solid-liquid ratio of the 2,6-pyridine dimethanol and the solvent is (2-3):10, in g / mL; the mass ratio of the 2,6-pyridine dimethanol to the hexamethylene diisocyanate is (4-6):7; In step (1.2), the mass ratio of hexamethylene diisocyanate to 1,4-butanediol is 2:1; the solid-liquid ratio of hexamethylene diisocyanate to solvent is 9:50, unit: g / mL; In step (1.3), the solid-liquid ratio of poly(N-isopropylacrylamide) to solvent is 3:20, unit: g / mL.

5. The method for preparing the intelligent humidity-controlling film with dual response to temperature and humidity according to claim 3, characterized in that: The mass ratio of 2,6-pyridine dimethanol in step (1.1) to 1,4-butanediol in step (1.2) is (20-30):9; In the reaction system of step (1.4), the ratio of the mass of poly(N-isopropylacrylamide) to the total mass of hexamethylene diisocyanate, 2,6-pyridine dimethanol and 1,4-butanediol is 3:(82-92).

6. The method for preparing the intelligent humidity-controlling film with dual response to temperature and humidity according to claim 1, characterized in that: Step (2) is specifically as follows: by solution casting, the polymer solution obtained in step (1) is spread on a glass plate by a film laying machine, and placed in a 40-60°C oven for 15-24 hours to obtain a temperature-humidity dual-responsive intelligent humidity-regulating film.

7. The method for preparing the intelligent humidity-controlling film with dual response to temperature and humidity according to claim 1, characterized in that: The thickness of the temperature-humidity dual-responsive humidity-regulating film prepared in step (2) is 20-50 μm.

8. The method for preparing the intelligent humidity-controlling film with dual response to temperature and humidity according to claim 1, characterized in that: The method further comprises step (3): loading the surface of the smart humidity-controlling film obtained in step (2) with an antibacterial substance to obtain a smart humidity-controlling film having antibacterial properties, temperature-controlling properties and humidity-controlling properties; The loading method is: spraying a tea polyphenol solution with a concentration of (1-4) g / L on the inner side of the humidity-adjustable film for antibacterial treatment.

9. An intelligent humidity-controlling film with dual response to temperature and humidity, prepared by the preparation method according to any one of claims 1 to 8, 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.

10. An application of the temperature and humidity dual-responsive intelligent humidity-control film with both humidity-control and antibacterial capabilities as claimed in claim 9, characterized in that: The intelligent humidity-regulating film is applied in the field of food preservation.

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