A dynamically cross-linked absorbent hydrogel and a method for its preparation

Abstract

The present application relates to a kind of dynamic crosslinking hygroscopic hydrogel and its preparation method.The raw materials include hydroxyl-containing water-soluble polymer material, boric acid crosslinking agent and hygroscopic salt material.The preparation method includes the preparation of gel precursor solution, the configuration of crosslinking agent solution, crosslinking reaction process and gelation process in mold.The borate ester bond crosslinking site in hydrogel can occur reversible hydrolysis reaction, and the crosslinking density of dynamic hydrogel is determined by the water content in gel.The dynamic crosslinking hygroscopic hydrogel with this characteristic has higher hygroscopic salt load and hygroscopic capacity than conventional covalent bond crosslinking hygroscopic hydrogel, faster hygroscopic / desorption kinetics performance and easy recycling, easy large-scale production characteristics.The present application also discloses the specific application of the dynamic crosslinking hygroscopic hydrogel, including solar air collection, closed space drying and dehumidification, evaporation heat dissipation and the like.

Description

Technical Field

[0001] This invention relates to the field of hygroscopic gel technology, specifically to a dynamic cross-linked hygroscopic hydrogel, its preparation method, and its application. Background Technology

[0002] Moisture in the air is an important natural resource, and many technologies have emerged to effectively utilize it, such as air-to-water collection, evaporative cooling, and humidification power generation. To achieve this utilization, hygroscopic hydrogels, with their high moisture absorption capacity and fast absorption rate, have become one of the core materials in technologies utilizing air moisture (Advanced Materials, 2022, 34, 2110079). Most reported hygroscopic hydrogels use a hydrophilic polymer network as a carrier, with hygroscopic salts as the main hygroscopic component dispersed within the polymer network. Invention patent CN 108059783 B discloses a hygroscopic hydrogel using sodium acrylate as a polymer carrier and magnesium chloride as the main active hygroscopic component. Invention patent CN 111363284 B discloses a composite hygroscopic gel material with a core-shell structure and doped with hygroscopic salts. However, all of the above materials suffer from the problem of leakage of the hygroscopic salt solution during the moisture absorption process. This is because the vast majority of existing hygroscopic hydrogels use polymer substrates that are irreversibly covalently cross-linked hydrogel materials. These salt-based hygroscopic hydrogels carry a risk of salt solution leakage during the hygroscopic process; that is, the rapid deliquescence of the salt leads to the separation of the salt solution from the hydrogel material, resulting in a decrease in the performance of the hygroscopic material.

[0003] To prevent leakage of salt solutions, porous structures are typically used to confine the salt solution within the hygroscopic material. However, the blockage of the hygroscopic solution leads to a decrease in hygroscopic kinetics. Patent application CN 116693928 A discloses a method for preparing macroporous hygroscopic hydrogels using an ice template method, which accelerates the kinetics of porous hygroscopic hydrogels to some extent. Other research has also explored preventing salt solution leakage by coating the surface of porous hygroscopic materials with a breathable hydrophobic layer (Cell Reports Physical Science 2021, 2(12), 100664). However, these methods are complex, increase the resistance to diffusion during hygroscopic processes, and do not address the phase separation problem between the salt solution and the polymer.

[0004] Given the aforementioned existing technologies, in order to ensure sufficient moisture absorption and stability of the hygroscopic gel during application, it is necessary to fundamentally solve the problem of salt leakage in the hygroscopic gel material. Therefore, it is necessary to find a technical solution that can ensure the material's moisture absorption performance while effectively preventing salt solution leakage during use. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides a method for preparing a dynamic hydrogel. Based on the reversible reaction between the crosslinking sites of the dynamic crosslinked hygroscopic gel and water, the degree of crosslinking of the dynamic crosslinked hygroscopic gel is related to its water content. When the internal water content of the dynamic crosslinked hygroscopic gel is high, the number of crosslinking sites decreases accordingly, the dynamic network changes from dense to sparse, and thus more water can swell. Therefore, the dynamic crosslinked hydrogel disclosed in this invention can fundamentally solve the problem of salt leakage in hygroscopic hydrogels. Secondly, due to the variability of the crosslinking network, as the water content of the dynamic crosslinking network increases, the diffusion of water in the dynamic crosslinking network is enhanced. Therefore, compared with covalently crosslinked hygroscopic hydrogels disclosed in other patents, the dynamic crosslinked hydrogel disclosed in this invention has faster hygroscopic kinetics.

[0006] A method for preparing a dynamically cross-linked hygroscopic gel, characterized by comprising the following steps:

[0007] (1) The hydroxyl-containing water-soluble polymer material is heated and dissolved in water. After cooling to room temperature, hygroscopic salt is added and stirred to dissolve, thus obtaining the precursor solution of the gel.

[0008] (2) Dissolve boric acid crosslinking agent in water at room temperature to obtain crosslinking agent solution.

[0009] (3) Heat the precursor solution of the gel obtained in step (1) and slowly add the crosslinking agent solution to the precursor solution of the gel while stirring rapidly to carry out the crosslinking reaction process and obtain a low crosslinking degree gel that maintains a certain fluidity.

[0010] (4) Dry and dehydrate the low cross-linking gel obtained in step (3) to increase the cross-linking degree of the material and obtain a dynamic cross-linked hygroscopic hydrogel.

[0011] This invention utilizes borate ester bonds as dynamic crosslinking sites, which can reversibly react with water at room temperature, dissociating into boric acid and alcohol. When the salt undergoes rapid deliquescence, the dynamic crosslinking network rapidly dissociates, allowing the salt solution to quickly diffuse into the gel, maintaining gel homogeneity. Even with increasing water content, the dynamically crosslinked hydrogel disclosed in this invention does not suffer from leakage of the salt solution due to moisture absorption exceeding the maximum swelling capacity of the crosslinking network. Therefore, the dynamically crosslinked hydrogel disclosed in this invention can achieve salt loading several times greater than the polymer mass while maintaining high stability during the moisture absorption-desorption cycle.

[0012] Preferably, in step (1), the hydroxyl-containing water-soluble polymer material is one of polyvinyl alcohol, poly(2,3-dihydroxypropyl acrylate), and poly(2-methyl-2-acrylate-2,3-dihydroxypropyl acrylate).

[0013] Preferably, in step (1), the hygroscopic salt is one of lithium chloride, calcium chloride, sodium sulfate, sodium chloride, and magnesium chloride.

[0014] Preferably, in step (1), the concentration of the hydroxyl-containing water-soluble polymer material in the precursor solution is 2~15wt%.

[0015] Preferably, in step (1), the mass ratio of the polymer to the hygroscopic salt is 1 / 1 to 1 / 10.

[0016] Preferably, in step (2), the boric acid crosslinking agent is sodium borate decahydrate or boric acid.

[0017] Preferably, in step (2), the concentration of the crosslinking agent solution is 0.1~5.0 wt%.

[0018] Because boronic acid ester bonds tend to decompose into boric acid and alcohol at high temperatures, the degree of crosslinking in dynamically crosslinked hydrogels decreases with increasing temperature under the same water content. To ensure that crosslinking points are uniformly distributed within the dynamically crosslinked hygroscopic hydrogel, a suitable temperature must be maintained during the crosslinking reaction.

[0019] Preferably, in step (3), the temperature of the crosslinking process is 60~100℃, the stirring speed is 500~1000rpm, and the reaction time is 2~10h.

[0020] Preferably, in step (4), the drying temperature is 80~100℃ and the time is 12~20h.

[0021] This invention also provides a photothermal dynamic hygroscopic hydrogel prepared using the above method for solar-powered air water collection. By adding photothermal materials to the dynamically cross-linked hygroscopic hydrogel, water in the hydrogel can be removed by solar energy. To ensure that the photothermal materials are uniformly dispersed in the dynamically cross-linked hydrogel, the prepared hydrogel needs to contain a certain amount of water before mixing.

[0022] Preferably, the photothermal material used to prepare the photothermal dynamic hydrogel is one of carbon powder, carbon nanotubes, or graphite powder.

[0023] Preferably, when the photothermal material is mixed into the dynamically cross-linked hygroscopic hydrogel, the water content of the dynamically cross-linked hygroscopic hydrogel is 50~70wt%.

[0024] Preferably, the amount of photothermal material mixed into the dynamically cross-linked hygroscopic hydrogel is 0.5~5wt%.

[0025] The photothermal dynamic crosslinking hygroscopic hydrogel of this invention can achieve photothermal conversion under one solar radiation intensity, realizing rapid desorption and water production. Due to its excellent kinetic properties, the photothermal dynamic hydrogel of this invention can achieve multiple adsorption-desorption cycles within a day, and the entire process requires no other form of energy input.

[0026] The dynamic cross-linked hygroscopic hydrogel of the present invention can also be used in the fields of dehumidification and evaporative heat dissipation in enclosed spaces.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) The borate ester dynamic cross-linking structure adopted in this invention gives the dynamic cross-linking hydrogel more characteristics of changing the degree of cross-linking with the size of the moisture absorption, so that the dynamic cross-linking moisture-absorbing hydrogel can swell in time during the moisture absorption process, effectively eliminating the salt solution leakage problem that is common in moisture-absorbing hydrogels.

[0029] (2) The dynamic cross-linked hygroscopic hydrogel prepared by the present invention can automatically change the polymer network from dense to sparse during the continuous hygroscopic process, thereby increasing the diffusion rate of water in the dynamic cross-linked hygroscopic hydrogel and making the hygroscopic / desorption kinetics of the dynamic cross-linked hygroscopic hydrogel faster than that of the covalent cross-linked hygroscopic hydrogel.

[0030] (3) The preparation process of the dynamic cross-linked hygroscopic hydrogel designed in this invention is simple, the raw materials are widely available, and the preparation process does not involve expensive experimental equipment, so it has good prospects for large-scale preparation.

[0031] (4) The dynamic cross-linked hydrogel prepared by the present invention can easily separate the hygroscopic salt and the polymer due to its reversible cross-linking sites. When the material completes its application life cycle, the raw materials can be easily recycled and reused, which is conducive to sustainable development.

[0032] (5) The dynamic cross-linked hydrogel prepared by the present invention has good plasticity and can be coated on various material substrates. It can be widely used in applications such as solar air water collection, dehumidification of closed spaces and evaporative heat dissipation. Attached Figure Description

[0033] Figure 1 This is a schematic diagram illustrating the principle of the dynamically cross-linked hygroscopic hydrogel of the present invention.

[0034] Figure 2 The following is a diagram showing the performance of the dynamically cross-linked hygroscopic hydrogel prepared in Case 1 in preventing salt leakage; where (1) is a photo of the dynamically cross-linked hygroscopic hydrogel after it has become saturated with moisture, and (2) is a photo of the conventional covalently cross-linked hygroscopic hydrogel after it has become saturated with moisture.

[0035] Figure 3The moisture absorption kinetics curves of the dynamically cross-linked hygroscopic hydrogel prepared in Case 1 at 90%RH and 25℃ are shown. Among them, 1 is the moisture absorption curve of the dynamically cross-linked hygroscopic hydrogel, and 2 is the moisture absorption curve of the conventional covalently cross-linked hygroscopic hydrogel.

[0036] Figure 4 To measure the moisture absorption of the dynamically cross-linked hygroscopic hydrogel prepared in Case 1 at various humidity levels at 25°C.

[0037] Figure 5 To implement the hygroscopic-solar desorption curve (70%RH, 25℃, 1 solar intensity) of the dynamically cross-linked hygroscopic hydrogel doped carbon nanotube powder prepared in Case 4. Detailed Implementation

[0038] The technical solution of the present invention will be further explained and described below with reference to several embodiments and accompanying drawings. However, the experimental conditions and setting parameters therein should not be regarded as limitations on the basic technical solution of the present invention. Furthermore, the scope of protection of the present invention is not limited to the following embodiments.

[0039] The embodiments of this invention achieve the preparation of dynamically cross-linked hygroscopic hydrogels by adjusting the polymer solution concentration, the amount of cross-linking agent added, the type of hygroscopic salt, the ratio of polymer to hygroscopic salt, and the amount of photothermal conversion material added. Example 1

[0040] The preparation steps of the dynamically cross-linked hygroscopic hydrogel in this embodiment are as follows:

[0041] (1) To prepare a 4wt% aqueous solution of polyvinyl alcohol, polyvinyl alcohol was heated to 90°C and dissolved in water. After cooling to room temperature, 16wt% lithium chloride was added and stirred to dissolve, thus obtaining a precursor solution for the gel.

[0042] (2) Dissolve sodium borate decahydrate crosslinking agent in water at room temperature to prepare a 0.8 wt% crosslinking agent solution.

[0043] (3) Heat the precursor solution of the gel to 70°C, and slowly add the crosslinking agent solution dropwise to the precursor solution of the gel while stirring rapidly to carry out the crosslinking reaction process, so as to obtain a low crosslinking degree gel that maintains a certain fluidity. The amount of crosslinking agent added is 2wt% of the polymer mass.

[0044] (4) Pour the obtained low cross-linked gel into a mold and dry it at 90°C for 12 hours to increase the cross-linking degree of the material and obtain a dynamic cross-linked hygroscopic hydrogel.

[0045] The performance of this implementation case was characterized by its resistance to salt solution leakage, moisture absorption kinetics curve, and moisture absorption capacity.

[0046] Figure 2The photographs of the dynamically cross-linked hygroscopic hydrogel prepared for this embodiment, after absorbing moisture to saturation at 90% RH and 25°C, show that in Figure (1), the dynamically cross-linked hygroscopic hydrogel maintains a complete gel state after moisture saturation without any salt solution leakage. Figure (2) shows a photograph of the covalently cross-linked hygroscopic hydrogel cross-linked using glutaraldehyde. After both hydrogels reached moisture saturation, the dynamically cross-linked hygroscopic hydrogel film maintained a complete gel state, while the bottom gel film of the covalently cross-linked hygroscopic hydrogel remained intact, but obvious salt solution precipitation occurred on the gel surface and collected at the bottom of the culture dish.

[0047] Figure 3 The moisture absorption kinetics curves of the dynamically cross-linked hygroscopic hydrogel prepared for this embodiment are shown in Figure 1 at 90% RH and 25℃. Figure 2 shows the kinetics curve of the dynamically cross-linked hygroscopic hydrogel and Figure 3 shows the kinetics curve of the covalently cross-linked hygroscopic hydrogel. A comparison of the two curves clearly shows that in the later stages of the moisture absorption process, the moisture absorption rate of the dynamically cross-linked hygroscopic hydrogel is significantly higher than that of the covalently cross-linked hygroscopic hydrogel.

[0048] Figure 4 The saturated moisture absorption capacity of the dynamically cross-linked hygroscopic hydrogel prepared in this embodiment was determined at 25℃ under different humidity levels. At relative humidity levels of 30%, 40%, 50%, 60%, 70%, 80%, and 90%, the moisture absorption capacities reached 1.02, 1.51, 1.73, 2.04, 2.43, 2.89, and 4.10 g / g, respectively. Example 2

[0049] The preparation steps of the dynamically cross-linked hygroscopic hydrogel in this embodiment are as follows:

[0050] (1) To prepare a 4wt% polyvinyl alcohol aqueous solution, polyvinyl alcohol was heated to 90°C and dissolved in water. After cooling to room temperature, 16wt% calcium chloride was added and stirred to dissolve, thus obtaining the precursor solution for the gel.

[0051] (2) Dissolve sodium borate decahydrate crosslinking agent in water at room temperature to prepare a 0.8 wt% crosslinking agent solution.

[0052] (3) Heat the precursor solution of the gel to 80°C, and slowly add the crosslinking agent solution dropwise to the precursor solution of the gel while stirring rapidly to carry out the crosslinking reaction process, so as to obtain a low crosslinking degree gel that maintains a certain fluidity. The amount of crosslinking agent added is 2wt% of the polymer mass.

[0053] (4) Pour the obtained low cross-linked gel into a mold and dry it at 90°C for 12 hours to increase the cross-linking degree of the material and obtain a dynamic cross-linked hygroscopic hydrogel. Example 3

[0054] The preparation steps of the dynamically cross-linked hygroscopic hydrogel in this embodiment are as follows:

[0055] (1) To prepare a 4wt% aqueous solution of polyvinyl alcohol, polyvinyl alcohol was heated to 90°C and dissolved in water. After cooling to room temperature, 8wt% lithium chloride was added and stirred to dissolve, thus obtaining a precursor solution for the gel.

[0056] (2) Dissolve the boric acid crosslinking agent in water at room temperature to prepare a 0.8 wt% crosslinking agent solution.

[0057] (3) Heat the precursor solution of the gel to 80°C, and slowly add the crosslinking agent solution dropwise to the precursor solution of the gel while stirring rapidly to carry out the crosslinking reaction process, so as to obtain a low crosslinking degree gel that maintains a certain fluidity. The amount of crosslinking agent added is 4 wt% of the polymer mass.

[0058] (4) Pour the obtained low cross-linked gel into a mold and dry it at 90°C for 12 hours to increase the cross-linking degree of the material and obtain a dynamic cross-linked hygroscopic hydrogel.

[0059] Example 4

[0060] To achieve desorption of the dynamically cross-linked hygroscopic hydrogel under sunlight irradiation, it is necessary to mix photothermal materials into the dynamically cross-linked hygroscopic hydrogel. The preparation steps of the dynamically cross-linked hygroscopic hydrogel in this embodiment are as follows:

[0061] (1) To prepare a 4wt% aqueous solution of polyvinyl alcohol, polyvinyl alcohol was heated to 90°C and dissolved in water. After cooling to room temperature, 16wt% lithium chloride was added and stirred to dissolve, thus obtaining a precursor solution for the gel.

[0062] (2) Dissolve sodium borate decahydrate crosslinking agent in water at room temperature to prepare a 0.8 wt% crosslinking agent solution.

[0063] (3) Heat the precursor solution of the gel to 70°C, and slowly add the crosslinking agent solution dropwise to the precursor solution of the gel while stirring rapidly to carry out the crosslinking reaction process, so as to obtain a low crosslinking degree gel that maintains a certain fluidity. The amount of crosslinking agent added is 2wt% of the polymer mass.

[0064] (4) Pour the obtained low cross-linked gel into a mold and dry it at 90°C for 12 hours to increase the cross-linking degree of the material and obtain a dynamic cross-linked hygroscopic hydrogel.

[0065] (5) Obtain the dried hygroscopic hydrogel and rehydrate it to a water content of 2g / g under the conditions of 70%RH and 25℃.

[0066] (6) Mix 1 wt% of carbon nanotube powder into the hygroscopic hydrogel so that the carbon nanotube powder is dispersed in the hygroscopic hydrogel.

[0067] (7) The obtained carbon nanotube-doped dynamically cross-linked hygroscopic hydrogel was subjected to a loading of 260 g / m 2 A surface density coating is applied to a metal substrate to form a dynamic cross-linked hygroscopic hydrogel adsorption bed.

[0068] The adsorption-desorption characterization of the carbon nanotube-doped dynamically cross-linked hygroscopic hydrogel prepared in this case was performed.

[0069] Figure 5 The carbon nanotube-doped dynamically crosslinked hygroscopic hydrogel adsorption bed prepared for this case study exhibits hygroscopic adsorption at 25℃ and 70%RH, and hygroscopic-solar desorption curves at 25℃, 50%RH, and under one solar cycle. It can complete one adsorption-desorption cycle within 4 hours, achieving a concentration of 450 g / m³. 2 The amount of water collected.

[0070] Comparison Case 1

[0071] The preparation steps of the covalently cross-linked hygroscopic hydrogel in this comparative case are as follows:

[0072] (1) To prepare a 4wt% aqueous solution of polyvinyl alcohol, polyvinyl alcohol was heated to 90°C and dissolved in water. After cooling to room temperature, 16wt% lithium chloride was added and stirred to dissolve, thus obtaining a precursor solution for the gel.

[0073] (2) Dissolve the glutaraldehyde crosslinking agent in water at room temperature to prepare a 2.5 wt% crosslinking agent solution.

[0074] (3) Heat the precursor solution of the gel to 70°C. While stirring rapidly, add 1 wt% acetic acid as a catalyst to the precursor solution of the gel. Then, slowly add the crosslinking agent solution to carry out the crosslinking reaction. To ensure that the molar amount of the crosslinking agent is consistent with that of the dynamically crosslinked hydrogel, the amount of crosslinking agent added is 3.33 wt% of the polymer mass. An incompletely reacted covalently crosslinked hydrogel is obtained.

[0075] (4) Pour the unreacted covalently cross-linked hydrogel into a mold and dry it at 90°C for 12 hours to increase the degree of cross-linking of the material and obtain a covalently cross-linked hygroscopic hydrogel.

Claims

1. A dynamically cross-linked hygroscopic hydrogel, characterized in that, The dynamically cross-linked hygroscopic hydrogel is composed of a polymer network dynamically cross-linked by borate ester bonds and a hygroscopic salt. The cross-linking points of the dynamically cross-linked polymer network can undergo reversible hydrolysis at room temperature, thereby achieving automatic adjustment of the degree of cross-linking during the hygroscopic process. The preparation method of the dynamically cross-linked hygroscopic hydrogel includes the following steps: (1) The hydroxyl-containing water-soluble polymer material is heated and dissolved in water, cooled to room temperature, and then hygroscopic salt is added and stirred to dissolve, thus obtaining the precursor solution of the gel; (2) Dissolve sodium borate decahydrate or boric acid crosslinking agent in water at room temperature to obtain a crosslinking agent solution; (3) Heat the precursor solution of the gel obtained in step (1) and slowly add the crosslinking agent solution to the precursor solution of the gel while stirring rapidly to carry out the crosslinking reaction process and obtain a low crosslinking degree gel that maintains a certain fluidity. (4) Dry and dehydrate the low cross-linking gel obtained in step (3) to increase the cross-linking degree of the material and obtain a dynamic cross-linked hygroscopic hydrogel; In step (1), the hydroxyl-containing water-soluble polymer material is polyvinyl alcohol, and the hygroscopic salt is lithium chloride, magnesium chloride, sodium chloride, calcium chloride or sodium sulfate; In step (1), the concentration of the hydroxyl-containing water-soluble polymer material in the precursor solution is 2-15 wt%, and the mass ratio of the hydroxyl-containing water-soluble polymer material to the hygroscopic salt is 1:1-1:

5. In step (2), the concentration of the crosslinking agent solution is 0.1-5.0 wt%; In step (3), the amount of crosslinking agent added is 2 wt% or 4 wt% of the mass of the hydroxyl-containing water-soluble polymer material.

2. The dynamically cross-linked hygroscopic hydrogel according to claim 1, characterized in that, The hygroscopic salt is lithium chloride.

3. The dynamically cross-linked hygroscopic hydrogel according to claim 1, characterized in that, In step (3), the temperature of the crosslinking reaction process is 60-100℃, the stirring speed is 500-1000rpm, and the reaction time is 2-10h.

4. The dynamically cross-linked hygroscopic hydrogel according to claim 1, characterized in that, In step (4), the drying temperature is 80-100℃ and the time is 12-20h.

5. A method for preparing the dynamically cross-linked hygroscopic hydrogel according to claim 1, characterized in that, Includes the following steps: (1) The hydroxyl-containing water-soluble polymer material is heated and dissolved in water, cooled to room temperature, and then hygroscopic salt is added and stirred to dissolve, thus obtaining the precursor solution of the gel; (2) Dissolve sodium borate decahydrate or boric acid crosslinking agent in water at room temperature to obtain a crosslinking agent solution; (3) Heat the precursor solution of the gel obtained in step (1) and slowly add the crosslinking agent solution to the precursor solution of the gel while stirring rapidly to carry out the crosslinking reaction process and obtain a low crosslinking degree gel that maintains a certain fluidity. (4) Dry and dehydrate the low cross-linking gel obtained in step (3) to increase the cross-linking degree of the material and obtain a dynamic cross-linked hygroscopic hydrogel; The hydroxyl-containing water-soluble polymer material is polyvinyl alcohol, and the hygroscopic salt is lithium chloride, magnesium chloride, sodium chloride, calcium chloride, or sodium sulfate. In step (1), the concentration of the hydroxyl-containing water-soluble polymer material in the precursor solution is 2-15 wt%, and the mass ratio of the hydroxyl-containing water-soluble polymer material to the hygroscopic salt is 1:1-1:

5. In step (2), the concentration of the crosslinking agent solution is 0.1-5.0 wt%; In step (3), the amount of crosslinking agent added is 2 wt% or 4 wt% of the mass of the hydroxyl-containing water-soluble polymer material.

6. The preparation method according to claim 5, characterized in that, The hygroscopic salt is lithium chloride.

7. The preparation method according to claim 5, characterized in that, In step (3), the crosslinking temperature is 60-100℃, the stirring speed is 500-1000rpm, and the reaction time is 2-10h.

8. The preparation method according to claim 5, characterized in that, In step (4), the drying temperature is 80-100℃ and the time is 12-20h.

9. The application of the dynamically cross-linked hygroscopic hydrogel according to any one of claims 1-4 or the dynamically cross-linked hygroscopic hydrogel prepared by the preparation method according to any one of claims 5-8 in solar air water collection, characterized in that, A photothermal material, namely carbon nanotubes, is mixed into the hydrogel.

10. The application of the dynamically cross-linked hygroscopic hydrogel according to any one of claims 1-4 or the dynamically cross-linked hygroscopic hydrogel prepared by the preparation method according to any one of claims 5-8 in dehumidification of enclosed spaces.

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