Nanofiber hydrogel moisture absorption composite film and preparation method thereof

Abstract

This invention discloses a nanofiber hydrogel hygroscopic composite film and its preparation method. The preparation method includes: preparing a brush-shaped polymer hydrogel microsphere dispersion using suspension polymerization; electrospinning polyacrylonitrile to obtain a nanofiber layer; spraying the hydrogel microsphere dispersion onto the surface of the nanofiber layer to form a hydrogel layer; repeating the electrospinning-spraying step at least once to obtain alternating stacked nanofiber and hydrogel layers; and finally loading hygroscopic salt. This invention constructs a multilayer heterogeneous structure through alternating electrospinning and spraying, allowing the hygroscopic salt to migrate to the nanofiber layer during adsorption-desorption, directly exposing it to the air, shortening the water vapor diffusion path, and improving hygroscopic kinetics. The polyethylene glycol side chains in the brush-shaped polymer hydrogel microspheres enhance the hydrophilicity of the hydrogel and reduce internal liquid diffusion resistance. This invention features a simple process and produces a film with excellent hygroscopic properties, suitable for air moisture collection and dehumidification.

Description

Technical Field

[0001] This invention relates to the field of moisture-absorbing materials technology, and more specifically to a nanofiber hydrogel moisture-absorbing composite film and its preparation method. Background Technology

[0002] In certain regions, freshwater scarcity has become a severe challenge due to limitations imposed by regional environmental conditions and insufficient freshwater production infrastructure. Atmospheric water harvesting technology, with its inherent ability to overcome geographical constraints and extract moisture from the surrounding air, is widely recognized as a major potential solution to regional water scarcity problems.

[0003] Hygroscopic salt composite hydrogels can efficiently absorb moisture from the air, and the swelling properties of the substrate ensure that the composite material has sufficient water capacity. During moisture absorption, the diffusion resistance in the hygroscopic salt composite hydrogel consists of both vapor diffusion resistance and liquid diffusion resistance. Existing research shows that the liquid diffusion resistance inside the hydrogel is much higher than the vapor diffusion resistance. Therefore, most research focuses on preparing hydrogel substrates with interconnected porous structures to reduce liquid diffusion distance and thus improve mass transfer efficiency. However, preparing interconnected porous hydrogels typically involves energy-intensive and time-consuming processes such as freeze-drying and low-temperature in-situ polymerization.

[0004] Therefore, it is of great significance to develop a novel hygroscopic material with excellent hygroscopic kinetic properties and a simple preparation process, as well as its preparation method. Summary of the Invention

[0005] In view of this, the present invention provides a nanofiber hydrogel moisture-absorbing composite film and its preparation method. By constructing a nanofiber-hydrogel multilayer structure, the moisture-absorbing salt tends to migrate to the surface of the nanofiber rather than remain in the pores of the hydrogel, so as to solve the problems of high internal liquid diffusion resistance and insufficient moisture absorption kinetics of existing moisture-absorbing materials.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing a nanofiber hydrogel moisture-absorbing composite film, comprising the following steps: Step 1: Preparation of brush-shaped polymer hydrogel microsphere dispersion Polyethylene glycol methyl ether methacrylate, acrylamide, polyethylene glycol diacrylate, and potassium persulfate are dissolved in water to form an aqueous phase; The aqueous phase was added dropwise to the oil phase containing cyclohexane and Span 80, and the temperature was raised to 70°C for polymerization reaction for 1 hour. After cooling to room temperature, deionized water was added to extract the hydrogel microspheres from the cyclohexane. The obtained brush-shaped hydrogel microspheres were collected, washed three times with deionized water, and redispersed in deionized water at a concentration of 50~100 mg / mL to obtain a brush-shaped polymer hydrogel microsphere dispersion. Step 2: Preparation of Nanofiber Layers Polyacrylonitrile was dissolved in N,N-dimethylformamide to obtain a spinning solution, and nanofiber layers were obtained by electrospinning. Step 3: Preparation of composite structure The brush-shaped polymer hydrogel microsphere dispersion obtained in step one is sprayed onto the surface of the nanofiber layer obtained in step two to form a hydrogel layer. Then, the electrospinning-spraying process is repeated at least once to obtain alternating stacked nanofiber layers and hydrogel layers as the initial film; Step 4: Loading the moisture-absorbing material The initial membrane material prepared in step three is washed with deionized water and ethanol alternately to remove impurities, dried, and then immersed in a hygroscopic salt solution. After soaking, it is dried to obtain a nanofiber hydrogel hygroscopic composite film.

[0007] Preferably, the amounts of polyethylene glycol methyl ether methacrylate, acrylamide, polyethylene glycol diacrylate, and potassium persulfate in step one, by mass, meet the following ranges: 0.5-1.4 parts of polyethylene glycol methyl ether methacrylate, 0.2-0.58 parts of acrylamide, 0.02-0.06 parts of polyethylene glycol diacrylate, and 0.080-0.096 parts of potassium persulfate; and the amount of water is 2-6 parts.

[0008] Preferably, in step one, the mass ratio of cyclohexane to Span 80 in the oil phase is 15-25:1, and the mass ratio of the water phase to the oil phase is 1:4-8.

[0009] Preferably, the mass ratio of polyacrylonitrile to N,N-dimethylformamide in the spinning solution in step two is 1:5~9.

[0010] Preferably, the conditions for electrospinning in step two are as follows: using a No. 20 metal needle, controlling the position of the needle and the structurer to be 12~20cm, the spinning flow rate to be 0.3~1.0mL / h, applying a +13kV high voltage to the spinning needle, using a grounded metal plate collector and maintaining a -5kV potential, spinning time for each nanofiber layer to be 30~60min, and controlling the thickness of the nanofiber layer to be 20~100µm.

[0011] Preferably, in step three, the amount of hydrogel dispersion sprayed is 1-3 mL, the thickness of the hydrogel layer is controlled to be 50-100 µm, and the electrospinning-spraying step is repeated 1-3 times to obtain a multilayer structure of nanofiber layer / hydrogel layer / nanofiber layer.

[0012] Preferably, the hygroscopic salt solution in step four is a hygroscopic salt aqueous solution with a mass fraction of 10% to 25%, and the hygroscopic salt is one of lithium chloride, calcium chloride, magnesium chloride, and sodium sulfate.

[0013] Preferably, before step four, the process further includes loading a photothermal material onto the outermost nanofiber layer of the initial film. The specific steps for loading the photothermal material are as follows: Pyrrole was dissolved in a 1.2 mol / L hydrochloric acid aqueous solution to obtain a precursor solution, and ammonium persulfate was dissolved in deionized water to obtain an oxidant solution. The precursor solution and the oxidant solution were sequentially sprayed onto the surface of the outermost nanofiber layer, and allowed to stand to allow the polymerization reaction to complete. Then, the mixture was rinsed with deionized water.

[0014] Preferably, the volume ratio of pyrrole to hydrochloric acid aqueous solution is 1:10~20; and the concentration of oxidant solution is 0.02~0.04 g / mL.

[0015] The present invention also provides a nanofiber hydrogel moisture-absorbing composite film prepared by any of the methods described above.

[0016] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a nanofiber hydrogel moisture-absorbing composite film and its preparation method, which has the following beneficial effects: (1) By alternating electrospinning and spraying processes, a multilayer heterostructure with alternating stacked nanofiber layers and hydrogel layers was constructed. This structure enables the migration of hygroscopic salts during the adsorption and desorption process, allowing the hygroscopic salts to be directly exposed to the air during the hygroscopic process, significantly shortening the water vapor diffusion path and improving the hygroscopic dynamics performance. (2) Brush-shaped polymer hydrogel microspheres are used as the hydrogel layer. The polyethylene glycol side chains enhance the hydrophilicity of the hydrogel, reduce the internal liquid diffusion resistance, and further improve the mass transfer efficiency. (3) The preparation process is simple, without the need for complicated freeze drying or low-temperature in-situ polymerization steps, and is easy to scale up for production; (4) It can be further loaded with photothermal materials (such as polypyrrole) to achieve solar-driven desorption and reduce energy consumption; (5) The nanofiber hydrogel hygroscopic composite film prepared by this method has excellent hygroscopic kinetic properties and good cycle stability. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0018] Figure 1 The hydrogel microspheres synthesized in Example 1 and their diameter distribution; Figure 2 The image shows the appearance of the composite moisture-absorbing membrane loaded with PPy prepared in Example 3; Figure 3 A comparison of the moisture absorption kinetics of the composite moisture-absorbing film (curve 1 in the figure) and microspheres (curve 2 in the figure) under the same conditions at 70% humidity; Figure 4 The results are the surface elemental analysis of the composite moisture-absorbing film and microspheres after drying. Figure 5 The moisture absorption kinetic curves of the conformal moisture-absorbing film under different humidity conditions; Figure 6 The images show the characterization before and after loading with hygroscopic salt. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 Preparation of brush-like hydrogel microspheres: Brush-shaped hydrogel microspheres were synthesized via suspension copolymerization of acrylamide and polyethylene glycol methyl ether methacrylate. 1.2 g of polyethylene glycol methyl ether methacrylate (number average molecular weight = 600 Da), 0.54 g of acrylamide, 0.05 g of polyethylene glycol diacrylate (number average molecular weight = 200 Da), and 0.088 g of potassium persulfate were dissolved in 4 mL of deionized water to form an aqueous dispersion.

[0021] 20 g of cyclohexane and 1 g of Span 80 were added to a 100 mL round-bottom flask equipped with a magnetic stirrer. Under mechanical stirring at 500 rpm, the aqueous phase was added dropwise to the oil phase over 10 minutes. The mixture was then heated to 70 °C and held at this temperature for 1 hour to initiate the polymerization reaction. After the reaction mixture cooled to room temperature, 30 mL of deionized water was added to extract the hydrogel microspheres from the cyclohexane. The resulting brush-shaped hydrogel microspheres were collected, washed three times with deionized water, and then redispersed in deionized water for later use. The synthesized hydrogel microspheres and their diameter distribution are shown in the figure. Figure 1 As shown.

[0022] Example 2 Preparation of nanofiber hydrogel moisture-absorbing composite films: Multilayer heterogeneous hygroscopic membranes were prepared using an alternating electrospinning-spraying process. 2 g of polyacrylonitrile was dissolved in 18 g of N,N-dimethylformamide to prepare the electrospinning solution. This solution was loaded into a plastic syringe equipped with a No. 20 metal needle, and spinning was performed at a flow rate of 0.5 mL / h. The receiving device for the electrospinning was a grounded metal plate collector with a diameter of 20 cm containing deionized water; a +13 kV high voltage was applied to the spinning needle, while the collector was maintained at a -5 kV potential.

[0023] After electrospinning for 30 minutes, 4 mL of the hydrogel microsphere dispersion prepared in Example 1 was taken and uniformly sprayed onto the surface of the obtained nanofiber layer. The above spinning-spraying cycle was repeated twice to obtain a three-layer membrane material (nanofiber layer / hydrogel layer / nanofiber layer). The obtained initial membrane was washed sequentially with deionized water and ethanol to remove impurities, dried, and cut into rectangular samples. These samples were then immersed in a 10% (w / w) lithium chloride aqueous solution to achieve salt loading. After draining off excess solution, the membrane was placed in an 80°C oven to dry overnight and stored for later use.

[0024] Example 3 Preparation of composite moisture-absorbing films supported on polypyrrole Based on Example 2, polypyrrole deposition was performed before loading hygroscopic salt.

[0025] First, a polymer precursor solution was prepared: 500 μL of pyrrole was dissolved in 5 mL of a 1.2 mol / L hydrochloric acid aqueous solution. Separately, an oxidant solution was prepared: 0.1 g of ammonium persulfate was dissolved in 5 mL of deionized water. Then, the polymer precursor solution and the oxidant solution were sequentially sprayed onto the surface of a pre-fabricated three-layer nanofiber / hydrogel / nanofiber membrane. The membrane was allowed to stand for 20 minutes to ensure complete polymerization. Finally, the resulting membrane was thoroughly rinsed three times with deionized water to remove residues, and then lithium chloride was loaded according to the method in Example 2 to obtain a composite hygroscopic membrane loaded with polypyrrole. Figure 2 As shown.

[0026] Experimental Example To verify the rapid moisture absorption behavior of the composite moisture-absorbing membrane, the moisture absorption kinetics of the composite moisture-absorbing membrane prepared in Example 2 were compared with those of the brush-shaped hydrogel microspheres prepared in Example 1. Both materials were loaded with the same mass fraction of lithium chloride (substrate mass / salt mass = 1:2), and the moisture absorption kinetics were tested at 25°C and 70% relative humidity.

[0027] The results are as follows Figure 3 As shown, under the same conditions, the overall moisture absorption capacity of the composite moisture-absorbing membrane and the brush-shaped hydrogel microspheres is similar (up to 2.4 g / g), but the moisture absorption rate differs significantly. After 30 minutes of initial moisture absorption, the composite moisture-absorbing membrane reaches 1.4 g / g, approximately twice that of the hydrogel microspheres. The composite moisture-absorbing membrane reaches 85% of its saturated moisture absorption capacity within 90 minutes, while the hydrogel microspheres require 300 minutes to reach the same level of moisture absorption. These results demonstrate that the composite moisture-absorbing membrane provided by this invention significantly improves moisture absorption kinetics.

[0028] Figure 4 For surface elemental analysis comparison, under the same salt loading, the chlorine content on the surface of the composite hygroscopic film is significantly higher than that on the microspheres, proving that the salt migrates towards the nanofiber layer during the desorption process.

[0029] Figure 5 The moisture absorption kinetics of the composite moisture-absorbing film under different humidity conditions are shown. The composite moisture-absorbing film exhibits the same moisture absorption kinetic behavior under different moisture absorption conditions.

[0030] Figure 6 Characterization images of the initial membrane prepared in Example 2 and the membrane material loaded with hygroscopic salt prepared in Example 3, from... Figure 6 It can be seen that the main structure of the membrane is an alternating stacked structure of nanofiber layers and hydrogel layers.

[0031] The various embodiments described in this specification are presented in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a nanofiber hydrogel moisture-absorbing composite film, characterized in that, Includes the following steps: Step 1: Preparation of brush-shaped polymer hydrogel microsphere dispersion Polyethylene glycol methyl ether methacrylate, acrylamide, polyethylene glycol diacrylate, and potassium persulfate are dissolved in water to form an aqueous phase; The aqueous phase was added dropwise to the oil phase containing cyclohexane and Span 80, and the temperature was raised to 70°C for polymerization reaction for 1 hour. After cooling to room temperature, deionized water was added to extract the hydrogel microspheres from the cyclohexane. The obtained brush-shaped hydrogel microspheres were collected, washed three times with deionized water, and redispersed in deionized water at a concentration of 50~100 mg / mL to obtain a brush-shaped polymer hydrogel microsphere dispersion. Step 2: Preparation of Nanofiber Layers Polyacrylonitrile was dissolved in N,N-dimethylformamide to obtain a spinning solution, and nanofiber layers were obtained by electrospinning. Step 3: Preparation of composite structure The brush-shaped polymer hydrogel microsphere dispersion obtained in step one is sprayed onto the surface of the nanofiber layer obtained in step two to form a hydrogel layer. Then, the electrospinning-spraying process is repeated at least once to obtain alternating stacked nanofiber layers and hydrogel layers as the initial film; Step 4: Loading the moisture-absorbing material The initial membrane material prepared in step three is washed with deionized water and ethanol alternately to remove impurities, dried, and then immersed in a hygroscopic salt solution. After soaking, it is dried to obtain a nanofiber hydrogel hygroscopic composite film.

2. The method for preparing a nanofiber hydrogel hygroscopic composite film according to claim 1, characterized in that, The amounts of polyethylene glycol methyl ether methacrylate, acrylamide, polyethylene glycol diacrylate, and potassium persulfate used in step one, by weight, meet the following ranges: 0.5-1.4 parts of polyethylene glycol methyl ether methacrylate, 0.2-0.58 parts of acrylamide, 0.02-0.06 parts of polyethylene glycol diacrylate, and 0.080-0.096 parts of potassium persulfate; the amount of water used is 2-6 parts.

3. The method for preparing a nanofiber hydrogel hygroscopic composite film according to claim 1, characterized in that, In step one, the mass ratio of cyclohexane to Span 80 in the oil phase is 15-25:1, and the mass ratio of the water phase to the oil phase is 1:4-8.

4. The method for preparing a nanofiber hydrogel hygroscopic composite film according to claim 1, characterized in that, In step two, the mass ratio of polyacrylonitrile to N,N-dimethylformamide in the spinning solution is 1:5~9.

5. The method for preparing a nanofiber hydrogel hygroscopic composite film according to claim 1, characterized in that, The conditions for electrospinning in step two are as follows: a No. 20 metal needle is used, the position of the needle and the structurer is controlled at 12~20cm, the spinning flow rate is 0.3~1.0mL / h, a +13kV high voltage is applied to the spinning needle, the receiving device is a grounded metal plate collector and maintains a -5kV potential, the spinning time of each nanofiber layer is 30~60min, and the thickness of the nanofiber layer is controlled at 20~100µm.

6. The method for preparing a nanofiber hydrogel hygroscopic composite film according to claim 1, characterized in that, In step three, the amount of hydrogel dispersion sprayed is 1~3mL, and the thickness of the hydrogel layer is controlled to be 50~100µm. The electrospinning-spraying step is repeated 1~3 times to obtain a multilayer structure of nanofiber layer / hydrogel layer / nanofiber layer.

7. The method for preparing a nanofiber hydrogel hygroscopic composite film according to claim 1, characterized in that, The hygroscopic salt solution mentioned in step four is a hygroscopic salt aqueous solution with a mass fraction of 10% to 25%, and the hygroscopic salt is one of lithium chloride, calcium chloride, magnesium chloride, and sodium sulfate.

8. The method for preparing a nanofiber hydrogel hygroscopic composite film according to claim 1, characterized in that, Before step four, the process also includes loading a photothermal material onto the outermost nanofiber layer of the initial film. The specific steps for loading the photothermal material are as follows: Pyrrole was dissolved in a 1.2 mol / L hydrochloric acid aqueous solution to obtain a precursor solution, and ammonium persulfate was dissolved in deionized water to obtain an oxidant solution. The precursor solution and the oxidant solution were sequentially sprayed onto the surface of the outermost nanofiber layer, and allowed to stand to allow the polymerization reaction to complete. Then, the mixture was rinsed with deionized water.

9. The method for preparing a nanofiber hydrogel hygroscopic composite film according to claim 8, characterized in that, The volume ratio of pyrrole to hydrochloric acid aqueous solution is 1:10~20; the concentration of oxidant solution is 0.02~0.04 g / mL.

10. A nanofiber hydrogel moisture-absorbing composite film prepared by the method according to any one of claims 1-9.

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