Preparation method of hydrogel film, hydrogel film and application

Abstract

The invention provides a preparation method of a hydrogel film, the hydrogel film and application, the preparation method comprises the following steps: S1, dissolving a polymer in a solvent I, and adding an aldehyde compound to obtain a polymer solution; s2, inorganic salt is dissolved in a solvent II, sulfuric acid is added, and a coagulating bath solution is obtained; s3, extruding and spreading the polymer solution on the surface of the coagulating bath solution to form a film, so as to obtain the hydrogel film. According to the prepared hydrogel film, spreading film forming and curing processes are combined, the preparation time of the hydrogel film is greatly shortened, and the problem that the hydrogel film is difficult to cure and form is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of polymer membranes, and particularly to a preparation method of a hydrogel membrane, the hydrogel membrane and applications thereof. Background Art

[0002] A hydrogel is a hydrophilic polymer with a three-dimensional network structure. In recent years, the diverse structures and hydrophilicity of hydrogels have attracted extensive attention, such as high elasticity, high water content, biocompatibility, and adjustable chemical and physical properties. As a high water absorption and water retention material, hydrogel membranes are widely used in various fields, such as the medical field, the agricultural field, the anti-corrosion field, etc. The coating method and the spraying method are commonly used as the preparation technologies for traditional hydrogel films. When using the coating method to prepare a hydrogel film, a polymer solution with a certain concentration is usually scraped onto a fixed substrate by a doctor blade and crosslinked under heating, ultraviolet light irradiation, or in an acidic environment to form a hydrogel film. When using the spraying method to prepare a hydrogel film, first, a polymer solution with a certain concentration is loaded into a spray gun, and then the solution is sprayed onto a molding substrate by adjusting the flow rate and the nozzle diameter of the spray gun, and generally, it needs to be sprayed several times to obtain a complete hydrogel film.

[0003] Although the above methods can achieve the preparation of defect-free hydrogel membranes, they are limited to small and medium-sized preparations in the laboratory and small-scale demand applications, and large-scale continuous preparation cannot be achieved industrially. In the process of preparing a film by the scraping method, the crosslinking process of the hydrogel takes a long time, and the forming depends on a doctor blade and a substrate with fixed sizes, and is assisted by means such as light and heat for forming. For example, Patent CN202211737181 discloses a composite pervaporation desalination membrane, its preparation method and applications, and uses the scraping method to prepare a film, but bubbles are likely to appear when using a doctor blade to prepare a film, resulting in film defects. In the process of preparing a film by the spraying method, the hydrogel membrane also needs to be formed depending on a fixed substrate, and the polymer solution is sprayed out of the spray gun and adheres to the substrate. The stability of this technology for forming is difficult to control, complicating the film preparation process, and it is more difficult to obtain a complete and uniform hydrogel film. For example, Patent CN202210354873 discloses a high-flux pervaporation membrane based on the spraying method, its preparation method and applications, and uses the spraying method to prepare a polymer film on a porous substrate, but the high operation requirements and the long forming process are still the limitations of the spraying method.

[0004] Neither of the two forming methods can achieve the preparation of a self-supporting hydrogel membrane, and the limitations of these molding technologies hinder the industrial preparation of hydrogel membranes. At present, it is still a challenge to achieve an ultra-thin self-supporting hydrogel membrane in the preparation process. Summary of the Invention

[0005] In the field of the preparation of hydrogel films, the technical means adopted in the prior art usually require a substrate for support. The present invention adopts a liquid surface film-forming technique, combines it with the conventional technique of hydrogel curing, and overcomes the technical problems that it is difficult to form and directionally spread the hydrogel film by regulating the concentration of sulfate ions. The successful combination of the two techniques forms a hydrogel film on the surface of the coagulation bath solution, getting rid of the dependence on the support substrate in the traditional method for preparing hydrogel films, and overcoming the problem that the structure of the hydrogel film is easily damaged when it is peeled off from the solid support substrate in the traditional method. This problem in the traditional method becomes more prominent when the thickness of the hydrogel film is thinner. The preparation method provided by the present invention can easily prepare a hydrogel film, and the film thickness of the prepared hydrogel film is adjustable. It can be used as a pervaporation membrane to separate liquid mixtures. The thinner the film, the further the separation flux is increased. It can also be applied in medical dressings and thin-film electronic devices.

[0006] The technical solution of the present invention is realized as follows: The present invention provides a method for preparing a hydrogel film, and the preparation method includes the following steps:

[0007] Step S1: Dissolve the polymer in solvent I, and then add an aldehyde compound to obtain a polymer solution;

[0008] Step S2: Dissolve the inorganic salt in solvent II, and then add sulfuric acid to obtain a coagulation bath solution;

[0009] Step S3: Extrude and spread the polymer solution on the surface of the coagulation bath solution to form a film, obtaining a hydrogel film;

[0010] The mass percentage concentration of the polymer solution is 4% - 15%;

[0011] In the coagulation bath solution, the concentration of sulfate ions is 0.5 - 1.3 mol / L.

[0012] Based on the above technical solutions, preferably, the mass percentage concentration of the polymer solution independently selects any value from 4%, 5%, 8%, 10%, 12%, 15% or the range value between any two of the above.

[0013] Based on the above technical solutions, preferably, in the coagulation bath solution, the concentration of sulfate ions independently selects any value from 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.3 mol / L or the range value between any two of the above.

[0014] Based on the above technical solutions, preferably, in step S1, the mass ratio of the polymer to solvent I is 1:3 - 1:27.

[0015] Based on the above technical solutions, preferably, in the step S1, the mass ratio of the polymer to the solvent I independently selects any value from 1:3, 1:7, 3:11, 1:11, 1:15, 1:22, 1:27 or the range value between any two of the above.

[0016] Based on the above technical solutions, preferably, in the step S2, the mass ratio of the inorganic salt to the solvent II is 1:16 - 21.

[0017] Based on the above technical solutions, preferably, in the step S2, the mass ratio of the inorganic salt to the solvent II independently selects any value from 1:16, 1:19, 1:20, 1:21 or the range value between any two of the above.

[0018] Based on the above technical solutions, preferably, the pH of the coagulation bath solution is 0.5 - 2.5.

[0019] Based on the above technical solutions, preferably, the pH of the coagulation bath solution independently selects any value from 0.5, 1, 1.5, 2, 2.5 or the range value between any two of the above.

[0020] Based on the above technical solutions, preferably, the mass ratio of the inorganic salt to the sulfuric acid is 4:2 - 10.

[0021] Based on the above technical solutions, preferably, the mass ratio of the inorganic salt to the sulfuric acid independently selects any value from 4:2, 4:3, 4:5, 4:6, 4:8, 4:10 or the range value between any two of the above.

[0022] Based on the above technical solutions, preferably, in the step S1, the polymer selects at least one of polyvinyl alcohol, polyethylene glycol, sodium alginate, chitosan;

[0023] The aldehyde compound selects at least one of glutaraldehyde, glyoxal, pentaerythritol tetraldehyde, terephthalaldehyde;

[0024] The solvent I selects at least one of N - methylpyrrolidone, N,N - dimethylformamide, dimethylacetamide, dimethyl sulfoxide, cyclohexanone, tetrahydrofuran.

[0025] Based on the above technical solutions, preferably, in the step S2, the inorganic salt selects at least one of sodium sulfate, sodium chloride, calcium sulfate, calcium chloride, magnesium sulfate, magnesium chloride.

[0026] Based on the above technical solutions, preferably, the solvent II selects at least one of water, N - methylpyrrolidone, N,N - dimethylformamide, dimethyl sulfoxide, cyclohexanone.

[0027] Based on the above technical solutions, preferably, in step S1, the temperature of the dissolution is 50 to 100 °C.

[0028] Based on the above technical solutions, preferably, in step S1, the temperature of the dissolution is independently selected from any value of 50 °C, 60 °C, 70 °C, 80 °C, 90 °C, 100 °C or the range value between any two of the above.

[0029] Based on the above technical solutions, preferably, in step S3, when extruding, an injection pump is used for extrusion.

[0030] According to another aspect of the present invention, there is provided a hydrogel film prepared by the above-mentioned preparation method, and the thickness of the dried hydrogel film is 50 nm to 30 μm.

[0031] Based on the above technical solutions, preferably, the thickness of the dried hydrogel film is independently selected from any value of 50 nm, 80 nm, 87.4 nm, 100 nm, 1 μm, 1.87 μm, 5.83 μm, 5.93 μm, 9 μm, 13 μm, 16.4 μm, 19.4 μm, 22.9 μm, 30 μm or the range value between any two of the above.

[0032] Based on the above technical solutions, preferably, the thickness of the dried hydrogel film is 86 nm to 23 μm.

[0033] According to still another aspect of the present invention, the present invention provides an application of the hydrogel film prepared by the above-mentioned preparation method, the above-mentioned hydrogel film in the fields of pervaporation membranes, separation of liquid mixtures, medical dressings, and thin film electronic devices.

[0034] In the preparation process of the hydrogel film of the present invention, by controlling the concentration of the polymer solution, the pH of the coagulation bath solution, and the concentration of sulfate ions, the directional spreading of the hydrogel film on the surface of the coagulation bath and the control of the thickness of the hydrogel film are achieved. Among them, when preparing the hydrogel film, the injection speed of the injection pump has no effect on the quality of the finally prepared hydrogel film, but the faster the injection pump speed, the faster the preparation process.

[0035] The preparation method of the hydrogel film of the present invention has the following beneficial effects compared with the prior art:

[0036] (1) In the field of preparation of hydrogel films, common techniques include doctor blade coating and spraying, and usually require a substrate and specific instruments. The preparation process of the hydrogel film prepared by the present invention can form a film without assembling cumbersome equipment and a specific substrate.

[0037] (2) After being coated on a substrate, the existing film-forming technology further requires catalysis or heating to cure the hydrogel film, which prolongs the preparation time of the hydrogel film. The hydrogel film prepared by the present invention combines the processes of spreading into a film and curing, greatly shortening the preparation time of the hydrogel film and overcoming the problem that the hydrogel film is difficult to cure and form.

[0038] (3) Due to the limitation of film formation on a specific substrate in the existing film-forming technology, the structure of the hydrogel film is easily damaged when the hydrogel film is peeled off from the solid support substrate. The thinner the prepared film is, the more prominent the defect problem is. The hydrogel film prepared by the present invention does not have the problem of peeling off from the solid support substrate within the thickness range of the prepared thin film, avoiding the problem that the thin film is easily damaged during peeling. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0040] Figure 1 Optical photograph of the thin film prepared by the present invention;

[0041] Figure 2 Schematic diagram of the technology for preparing the hydrogel film by the present invention;

[0042] Figure 3 Schematic diagram of excessive spreading during the preparation process of the technology for preparing the hydrogel film by the present invention;

[0043] Figure 4 Schematic diagram of directional spreading during the preparation process of the technology for preparing the hydrogel film by the present invention;

[0044] Figure 5 Schematic diagram of restricted spreading during the preparation process of the technology for preparing the hydrogel film by the present invention;

[0045] Figure 6 Schematic diagram of excessive spreading in Comparative Example 2 of the present invention;

[0046] Figure 7 Schematic diagram of excessive spreading in Comparative Example 4 of the present invention;

[0047] Figure 8 Schematic diagram of excessive spreading in Comparative Example 6 of the present invention;

[0048] Figure 9 Schematic diagram of directional spreading of the hydrogel film prepared in Example 2 of the present invention;

[0049] Figure 10Schematic diagram of the limited paving for Comparative Example 3 of the present invention;

[0050] Figure 11 Schematic diagram of the limited paving for Comparative Example 1 of the present invention;

[0051] Figure 12 Schematic diagram of the limited paving for Comparative Example 5 of the present invention;

[0052] Figure 13 SEM image of the film thickness of Example 1 of the present invention;

[0053] Figure 14 SEM image of the film thickness of Example 2 of the present invention;

[0054] Figure 15 SEM image of the film thickness of Example 3 of the present invention;

[0055] Figure 16 SEM image of the film thickness of Example 4 of the present invention;

[0056] Figure 17 SEM image of the film thickness of Example 5 of the present invention;

[0057] Figure 18 SEM image of the film thickness of Example 6 of the present invention;

[0058] Figure 19 SEM image of the film thickness of Example 7 of the present invention;

[0059] Figure 20 SEM image of the film thickness of Example 8 of the present invention;

[0060] Figure 21 SEM image of the film thickness of Example 9 of the present invention. Detailed implementation manners

[0061] Next, in combination with the implementation manners of the present invention, the technical solutions in the implementation manners of the present invention will be clearly and completely described. Obviously, the described implementation manners are only a part of the implementation manners of the present invention, rather than all the implementation manners. Based on the implementation manners in the present invention, all other implementation manners obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0062] The optical photograph of the hydrogel film prepared by using the preparation method of the hydrogel film of the present invention is as Figure 1As shown, the film prepared by the method of the present invention has good light transmittance, the film is complete, and no substrate support is required; the hydrogel film of the present invention is prepared by extruding and spreading a polymer solution on the surface of a coagulation bath solution, while generating crosslinking, and forming a hydrogel film on the surface of the coagulation bath solution( Figure 2 ); according to the preparation method of the present invention, the sulfate ion concentration in the coagulation bath solution is controlled at 0.5-1.3 mol / L, and at the same time, when the mass percentage of PVA is controlled at 4-15%, the directional spreading of the hydrogel can be realized, and the cross-sectional thickness of the directionally spread hydrogel film is controllable( Figure 4 As shown); when the sulfate ion concentration is less than 0.5 mol / L, the hydrogel film spreads excessively near the injection port( Figure 3 As shown), which will cause the spreading direction of the film to be uncontrollable, and the film edge contacts and adheres to the inner wall of the water tank, resulting in film breakage; when the sulfate ion concentration is greater than 1.3 mol / L, the directional spreading of the hydrogel film is limited( Figure 5 As shown), the film cannot spread in time and fully, and the polymer solution accumulates and solidifies near the injection port, resulting in the inability to form a film.

[0063] The preparation method of the hydrogel film of the present invention will be introduced in detail below in conjunction with examples.

[0064] Example 1

[0065] Step 1: Take 1 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000 and dissolve them in 7 g of N-methylpyrrolidone (NMP), stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0066] Step 2: Add 2 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 10% polymer solution.

[0067] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder and add it to 427.5 g of deionized water, completely dissolve it to prepare a 45 g / L sodium sulfate solution, and add 50 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0068] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution into a film through an injection pump.

[0069] The process of spreading the PVA solution through the surface tension difference and the process of acid-catalyzed crosslinking of PVA in the coagulation bath restrict each other to reach an equilibrium, enabling the directional spreading in the hydrogel molding process. The film thickness is 19.4 μm. The specific experimental results are shown in Table 1. As Figure 13 shown, it can be seen from Figure 13 that the thickness of the hydrogel film is 19.4 μm.

[0070] Example 2

[0071] Step 1: Take 1 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000 and dissolve them in 7 g of N-methylpyrrolidone (NMP). Stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0072] Step 2: Add 2 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 10% polymer solution.

[0073] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder and add it to 442.5 g of deionized water. Completely dissolve it to prepare a 45 g / L sodium sulfate solution. Add 35 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0074] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0075] The process of spreading the PVA solution through the surface tension difference and the process of acid-catalyzed cross-linking of PVA in the coagulation bath restrict each other and reach an equilibrium, enabling the process of making the hydrogel mold to achieve directional spreading ( Figure 9 as shown). Directional spreading can control the film thickness, and the film thickness is 9 μm. The specific experimental results are shown in Table 1. As Figure 14 shown, it can be seen from Figure 14 that the thickness of the hydrogel film is 9 μm.

[0076] Example 3

[0077] Step 1: Take 1 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000 and dissolve them in 7 g of N-methylpyrrolidone (NMP). Stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0078] Step 2: Add 2 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 10% polymer solution.

[0079] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder and add it to 467.5 g of deionized water. Completely dissolve it to prepare a 45 g / L sodium sulfate solution. Add 10 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0080] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0081] The process of spreading the PVA solution through the surface tension difference and the process of acid-catalyzed cross-linking of PVA in the coagulation bath restrict each other and reach an equilibrium, enabling the process of making the hydrogel mold to achieve directional spreading. The film thickness is 1.87 μm. The specific experimental results are shown in Table 1. As Figure 15 shown, it can be seen from Figure 15It can be seen that the thickness of the hydrogel film is 1.87 μm.

[0082] Comparative Example 1

[0083] Step 1: Take 1 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000 and dissolve them in 7 g of N-methylpyrrolidone (NMP). Stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0084] Step 2: Add 2 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 10% polymer solution.

[0085] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder and add it to 422.5 g of deionized water. Completely dissolve it to prepare a 45 g / L sodium sulfate solution. Add 55 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0086] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0087] As Figure 11 shown, due to the excessive acid concentration in the coagulation bath solution, the hydrogel cures too quickly, resulting in limited spreading during the molding process and unable to form a film. No thickness photos were taken.

[0088] Comparative Example 2

[0089] Step 1: Take 1 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000 and dissolve them in 7 g of N-methylpyrrolidone (NMP). Stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0090] Step 2: Add 2 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 10% polymer solution.

[0091] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder and add it to 472.5 g of deionized water. Completely dissolve it to prepare a 45 g / L sodium sulfate solution. Add 5 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0092] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0093] As Figure 6 shown, due to the too low acid concentration in the coagulation bath solution, the hydrogel cures too slowly, resulting in excessive spreading during the molding process and the molding process cannot be controlled. No thickness photos were taken.

[0094] Example 4

[0095] Step 1: Take 1.5 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000, dissolve them in 5.5 g of N-methylpyrrolidone (NMP), and stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0096] Step 2: Add 3 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 15% polymer solution.

[0097] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder, add it to 427.5 g of deionized water, completely dissolve it to prepare a 45 g / L sodium sulfate solution, and add 50 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0098] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0099] The process of spreading the PVA solution through the surface tension difference and the process of acid-catalyzed cross-linking of PVA in the coagulation bath restrict each other to reach an equilibrium, enabling the directional spreading in the hydrogel molding process. The film thickness is 22.9 μm. The specific experimental results are shown in Table 1. As Figure 16 shown, it can be seen from Figure 16 that the thickness of the hydrogel film is 22.9 μm.

[0100] Example 5

[0101] Step 1: Take 1.5 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000, dissolve them in 5.5 g of N-methylpyrrolidone (NMP), and stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0102] Step 2: Add 3 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 15% polymer solution.

[0103] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder, add it to 442.5 g of deionized water, completely dissolve it to prepare a 45 g / L sodium sulfate solution, and add 35 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0104] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0105] The process of spreading the PVA solution through the surface tension difference and the process of acid-catalyzed cross-linking of PVA in the coagulation bath restrict each other to reach an equilibrium, enabling the directional spreading in the hydrogel molding process. The film thickness is 16.4 μm. The specific experimental results are shown in Table 1. As Figure 17 shown, it can be seen from Figure 17 that the thickness of the hydrogel film is 16.4 μm.

[0106] Example 6

[0107] Step 1: Take 1.5 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000 and dissolve them in 5.5 g of N-methylpyrrolidone (NMP). Stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0108] Step 2: Add 3 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 15% polymer solution.

[0109] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder and add it to 467.5 g of deionized water. Completely dissolve it to prepare a 45 g / L sodium sulfate solution. Add 10 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0110] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0111] The process of spreading the PVA solution through the surface tension difference and the process of acid-catalyzed cross-linking of PVA in the coagulation bath restrict each other to reach equilibrium, enabling the hydrogel molding process to achieve directional spreading. The film thickness is 5.83 μm. The specific experimental results are shown in Table 1. As Figure 18 shown, it can be seen from Figure 18 that the thickness of the hydrogel film is 5.83 μm.

[0112] Comparative Example 3

[0113] Step 1: Take 1.5 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000 and dissolve them in 5.5 g of N-methylpyrrolidone (NMP). Stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0114] Step 2: Add 3 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 15% polymer solution.

[0115] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder and add it to 422.5 g of deionized water. Completely dissolve it to prepare a 45 g / L sodium sulfate solution. Add 55 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0116] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0117] As Figure 10 shown, due to the too high acid concentration in the coagulation bath solution, the hydrogel cures too fast, restricting the spreading during the molding process and preventing film formation. No thickness photo was taken.

[0118] Comparative Example 4

[0119] Step 1: Take 1.5 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000, dissolve them in 5.5 g of N-methylpyrrolidone (NMP), and stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0120] Step 2: Add 3 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 15% polymer solution.

[0121] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder, add it to 472.5 g of deionized water, completely dissolve it to prepare a 45 g / L sodium sulfate solution, and add 5 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0122] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0123] As Figure 7 shown, due to the too low acid concentration of the coagulation bath solution, the hydrogel curing is too slow, resulting in excessive spreading during the molding process, the molding process cannot be controlled, and no thickness photos are taken.

[0124] Example 7

[0125] Step 1: Take 0.4 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000, dissolve them in 8.8 g of N-methylpyrrolidone (NMP), and stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0126] Step 2: Add 0.8 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 4% polymer solution.

[0127] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder, add it to 427.5 g of deionized water, completely dissolve it to prepare a 45 g / L sodium sulfate solution, and add 50 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0128] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0129] The process of spreading the PVA solution through the surface tension difference and the process of acid-catalyzed cross-linking of PVA in the coagulation bath restrict each other to reach an equilibrium, enabling the directional spreading of the hydrogel molding process. The thickness of the film is 13 μm. The specific experimental results are shown in Table 1. As Figure 19 shown, it can be seen from Figure 19 that the thickness of the hydrogel film is 13 μm.

[0130] Example 8

[0131] Step 1: Take 0.4 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000, dissolve them in 8.8 g of N-methylpyrrolidone (NMP), and stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0132] Step 2: Add 0.8 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 4% polymer solution.

[0133] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder, add it to 442.5 g of deionized water, completely dissolve it to prepare a 45 g / L sodium sulfate solution, and add 35 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0134] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0135] The process of spreading the PVA solution through the surface tension difference and the process of acid-catalyzed cross-linking of PVA in the coagulation bath restrict each other to reach equilibrium, enabling the process of making the hydrogel mold to achieve directional spreading. The thickness of the film is 5.93 μm. The specific experimental results are shown in Table 1. As Figure 20 shown, it can be seen from Figure 20 that the thickness of the hydrogel film is 5.93 μm.

[0136] Example 9

[0137] Step 1: Take 0.4 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000, dissolve them in 8.8 g of N-methylpyrrolidone (NMP), and stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0138] Step 2: Add 0.8 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 4% polymer solution.

[0139] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder, add it to 467.5 g of deionized water, completely dissolve it to prepare a 45 g / L sodium sulfate solution, and add 10 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0140] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0141] The process of spreading the PVA solution through the surface tension difference and the process of acid-catalyzed cross-linking of PVA in the coagulation bath restrict each other to reach equilibrium, enabling the process of making the hydrogel mold to achieve directional spreading. The thickness of the film is 87.4 nm. The specific experimental results are shown in Table 1. As Figure 21 shown, it can be seen from Figure 21 that the thickness of the hydrogel film is 87.4 nm.

[0142] Comparative Example 5

[0143] Step 1: Take 0.4 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000, dissolve them in 8.8 g of N-methylpyrrolidone (NMP), and stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0144] Step 2: Add 0.8 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 4% polymer solution.

[0145] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder, add it to 422.5 g of deionized water, completely dissolve it to prepare a 45 g / L sodium sulfate solution, and add 55 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0146] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0147] As Figure 12 shown, due to the too high acid concentration of the coagulation bath solution, the hydrogel cures too fast, resulting in limited spreading during the molding process and unable to form a film, and no thickness photos were taken.

[0148] Comparative Example 6

[0149] Step 1: Take 0.4 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000, dissolve them in 8.8 g of N-methylpyrrolidone (NMP), and stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0150] Step 2: Add 0.8 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 4% polymer solution.

[0151] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder, add it to 472.5 g of deionized water, completely dissolve it to prepare a 45 g / L sodium sulfate solution, and add 5 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0152] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0153] As Figure 8 shown, due to the too low acid concentration of the coagulation bath solution, the hydrogel cures too slowly, resulting in excessive spreading during the molding process and the molding process cannot be controlled, and no thickness photos were taken.

[0154] Comparative Example 7

[0155] Step 1: Take 1.6 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000, dissolve them in 5.2 g of N-methylpyrrolidone (NMP), and stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0156] Step 2: Add 3.2 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 16% polymer solution.

[0157] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder, add it to 442.5 g of deionized water, completely dissolve it to prepare a 45 g / L sodium sulfate solution, and add 35 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0158] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0159] The excessive concentration of the PVA solution restricted the spreading process and prevented film formation, so no thickness photos were taken.

[0160] Comparative Example 8

[0161] Step 1: Take 0.3 g of polyvinyl alcohol (PVA) particles with a molecular weight of 215,000, dissolve them in 9.1 g of N-methylpyrrolidone (NMP), and stir and heat to 80 °C until completely dissolved to obtain a PVA solution.

[0162] Step 2: Add 0.6 g of 50% glutaraldehyde (GA) aqueous solution to the above PVA solution to obtain a 3% polymer solution.

[0163] Step 3: Take 22.5 g of anhydrous sodium sulfate (Na2SO4) powder, add it to 442.5 g of deionized water, completely dissolve it to prepare a 45 g / L sodium sulfate solution, and add 35 g of sulfuric acid to the sodium sulfate solution to obtain a coagulation bath solution.

[0164] Step 4: Extrude and spread the polymer solution on the surface of the coagulation bath solution through an injection pump to form a film.

[0165] The too low concentration of the PVA solution caused excessive spreading during the film-making process, and the film-making process could not be controlled, so no thickness photos were taken.

[0166] Table 1 Thickness table of hydrogel films in examples and comparative examples

[0167]

[0168]

[0169] As can be seen from Table 1, by comparing Examples 1-3 with Comparative Examples 1-2, Examples 4-6 with Comparative Examples 3-4, and Examples 7-9 with Comparative Examples 5-6, when the sulfate ion concentration is too high or too low, the spreading of the hydrogel film is restricted or the process cannot be controlled, and the hydrogel film cannot be prepared. By comparing Example 2 with Comparative Examples 7 and 8, it is found that when the concentration of polyvinyl alcohol is too high or too low, the spreading of the hydrogel film is restricted or excessive spreading occurs, and the film-forming process cannot be controlled, and the hydrogel film cannot be prepared.

[0170] The foregoing are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a hydrogel film, characterized in that, The preparation method includes the following steps: Step S1: Dissolve the polymer in Solvent I, and then add an aldehyde compound to obtain a polymer solution; Step S2: Dissolve the inorganic salt in Solvent II, and then add sulfuric acid to obtain a coagulation bath solution; Step S3: Extrude and spread the polymer solution on the surface of the coagulation bath solution to form a film, obtaining a hydrogel film; The mass percentage concentration of the polymer solution is 4% to 15%; In the coagulation bath solution, the concentration of sulfate ions is 0.5 to 1.3 mol / L.

2. The preparation method according to claim 1, characterized in that, In Step S1, the mass ratio of the polymer to Solvent I is 1:3 to 1:

27.

3. The preparation method according to claim 1, characterized in that, In Step S2, the mass ratio of the inorganic salt to Solvent II is 1:16 to 21; The pH of the coagulation bath solution is 0.5 to 2.5; The mass ratio of the inorganic salt to the sulfuric acid is 4:2 to 10.

4. The preparation method according to claim 1, wherein In Step S1, the polymer is selected from at least one of polyvinyl alcohol, polyethylene glycol, sodium alginate, and chitosan; The aldehyde compound is selected from at least one of glutaraldehyde, glyoxal, pentaerythritol tetraldehyde, and terephthalaldehyde; Solvent I is selected from at least one of N-methylpyrrolidone, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, cyclohexanone, and tetrahydrofuran.

5. The preparation method according to claim 1, characterized in that, In Step S2, the inorganic salt is selected from at least one of sodium sulfate, sodium chloride, calcium sulfate, calcium chloride, magnesium sulfate, and magnesium chloride.

6. The preparation method according to claim 1, characterized in that, In Step S2, Solvent II is selected from at least one of water, N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, cyclohexanone, and tetrahydrofuran; In Step S1, the temperature of the dissolution is 50 to 100 °C.

7. The preparation method according to claim 1, characterized in that, In Step S3, during the extrusion, an injection pump is used for extrusion.

8. The hydrogel film prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The thickness of the dried hydrogel film is 50 nm to 30 μm.

9. The hydrogel film according to claim 8, wherein The thickness of the dried hydrogel film is 86 nm to 23 μm.

10. Applications of the hydrogel film prepared by the preparation method according to any one of claims 1-7 and the hydrogel film according to claim 8 or 9 in the fields of pervaporation membranes, separation of liquid mixtures, medical dressings, and thin film electronic devices.

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