Hydrogel as well as preparation and application thereof

Abstract

The invention discloses hydrogel as well as preparation and application thereof, and belongs to the field of high polymer materials. The preparation method of the hydrogel comprises the following steps: mixing sodium alginate with a free radical initiator, and then adding acrylic acid for mixing reaction to obtain sodium alginate grafted with acrylic acid; the sodium alginate grafted with the acrylic acid and N, N-methylene bisacrylamide are mixed and crosslinked, and the hydrogel is obtained. The natural polymer hydrogel not only has high water absorption, but also has better mechanical strength and mechanical property.

Description

Technical Field

[0001] The present application relates to the field of polymer materials, and in particular to a hydrogel and its preparation and application. Background Art

[0002] Compared with traditional absorbent materials (such as pulp, cotton and sponges), superabsorbent polymer hydrogel material is a micro-cross-linked hydrophilic polymer that can swell, absorb and retain hundreds or even thousands of times its own weight in water, and can retain the absorbed water well even under pressure.

[0003] However, existing technologies often exhibit low recoverability of highly absorbent hydrogels, resulting in mechanical properties that are characterized by low toughness and high brittleness. However, applications in gardening, desert water conservation, agriculture, and other fields require both sustained water absorption and excellent mechanical properties, limiting the application of highly absorbent hydrogels in these areas.

[0004] In addition, hydrogel materials prepared by chemical synthesis are difficult to degrade naturally in the environment. Therefore, a large number of hydrogel materials prepared by chemical synthesis may bring potential environmental pollution problems, which further limits their application in agriculture and horticulture. Natural polymer hydrogel materials generally have good biocompatibility, environmental friendliness and responsiveness to external stimuli. Therefore, natural polymer hydrogels prepared from natural biopolysaccharides such as chitosan (CTS), agar, dextrin, cellulose, starch and protein have received widespread attention in recent years.

[0005] Therefore, there is an urgent need for a natural polymer hydrogel material with both good water absorption and mechanical properties. Summary of the Invention

[0006] In view of this, the present application provides a hydrogel and its preparation and application, aiming to provide a natural polymer hydrogel material with good water absorption and mechanical properties.

[0007] The embodiment of the present application is implemented as follows:

[0008] In a first aspect, the present application provides a method for preparing a hydrogel, comprising: mixing sodium alginate with a free radical initiator, then adding acrylic acid for mixed reaction to obtain sodium alginate grafted with acrylic acid; mixing and cross-linking the sodium alginate grafted with acrylic acid with N,N-methylenebisacrylamide to obtain a hydrogel.

[0009] In some embodiments, the free radical initiator is selected from ammonium persulfate ((NH4)2S2O8); and / or,

[0010] The mass ratio of the free radical initiator to the sodium alginate is (1-5):100; and / or,

[0011] The mass ratio of the acrylic acid to the sodium alginate is (5-9):1; and / or,

[0012] The mass ratio of the N,N-methylenebisacrylamide to the acrylic acid is 0.4% to 2%.

[0013] In some embodiments, the step of mixing sodium alginate with a free radical initiator and then adding acrylic acid for mixed reaction to obtain sodium alginate grafted with acrylic acid specifically comprises: heating an aqueous solution of sodium alginate to 65-75° C. in an oxygen-free atmosphere, then adding the free radical initiator, maintaining the temperature at 65-75° C. for a dehydrogenation reaction for 5-15 minutes, then cooling the temperature to 25-35° C., adding acrylic acid, and reacting for 5-10 minutes to obtain sodium alginate grafted with acrylic acid.

[0014] In some embodiments, the mass volume concentration of sodium alginate in the aqueous solution of sodium alginate is 2-5 w / v%; and / or the free radical initiator is in the form of an aqueous solution with a mass volume concentration of (0.01-0.02) g:5 mL; and / or the acrylic acid is added in the form of an acrylic acid aqueous solution with a mass volume concentration of (5-10) g:10 mL.

[0015] In some embodiments, the mixing and cross-linking of the sodium alginate grafted with acrylic acid and N,N-methylenebisacrylamide specifically includes: adding N,N-methylenebisacrylamide to the sodium alginate grafted with acrylic acid, and mixing and reacting at 25-35° C. for 20-40 minutes.

[0016] In some embodiments, after obtaining the hydrogel, the method further comprises:

[0017] Providing a metal ion solution, wherein the metal ion solution includes one or more metal ions selected from the group consisting of calcium ions, lithium ions, strontium ions, and aluminum ions;

[0018] The hydrogel is subjected to a cross-linking reaction with the metal ion solution to obtain a metal ion coordinated hydrogel.

[0019] In some embodiments, the metal ion solution includes an aqueous solution formed by one or more of anhydrous calcium chloride, lithium chloride, strontium chloride hexahydrate, and aluminum chloride hexahydrate; and / or,

[0020] The molar concentration of metal ions in the metal ion solution is 0.1 to 0.3 Mol / L.

[0021] In some embodiments, cross-linking the hydrogel with the metal ion solution specifically includes: immersing the hydrogel in the metal ion solution and performing the cross-linking reaction for 10 to 15 hours.

[0022] In a second aspect, the present application provides a hydrogel prepared by the above-mentioned preparation method.

[0023] In a third aspect, the present application provides applications of hydrogels in agriculture, horticulture, desert soil and water moisture retention and gel drives, as well as drug delivery systems and water-blocking tapes.

[0024] The hydrogel preparation method of the present application comprises mixing sodium alginate with a free radical initiator, then adding acrylic acid for a mixed reaction to obtain sodium alginate grafted with acrylic acid; and then mixing and cross-linking the acrylic acid grafted sodium alginate with N,N-methylenebisacrylamide to obtain a hydrogel. This natural polymer hydrogel not only has high water absorption, but also exhibits good mechanical strength and mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 This is a schematic flow chart of an embodiment of a method for preparing a hydrogel provided by the present application;

[0027] Figure 2 This is a schematic diagram of the preparation process of acrylic acid grafted sodium alginate hydrogel;

[0028] Figure 3 is the infrared spectrum of acrylic acid before and after grafting onto sodium alginate in Example 1;

[0029] Figures 4 to 8 Electron microscopic images of the hydrogels of Example 1 and Examples 10-12, respectively;

[0030] Figure 9 1 is a time-water absorption graph of the hydrogels of Comparative Example 1 and Examples 1-5;

[0031] Figure 10 is a time-water absorption rate graph of the hydrogels of Example 2 and Examples 6-8;

[0032] Figure 11 This is a physical display of the hydrogels of Comparative Example 1 and Examples 1 to 5;

[0033] Figure 12The figures show the hydrogels of Examples 1 and 10;

[0034] Figure 13 is a compression stress-strain curve graph of the hydrogels of Examples 10, 14-17 and Comparative Example 1;

[0035] Figure 14 is a cyclic compression test graph of the hydrogel in Example 17;

[0036] Figure 15 This is a compression test diagram of the hydrogel in Example 10. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present application. In addition, it should be understood that the specific implementation methods described herein are only used to illustrate and explain the present application and are not used to limit the present application. In the present application, unless otherwise specified, the directional words used, such as "upper" and "lower", are specifically the directions of the drawings in the accompanying drawings. In addition, in the description of the present application, the term "including" means "including but not limited to".

[0038] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0039] In this application, "and / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0040] In this application, "at least one" means one or more, and "plurality" means two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0041] This application uses sodium alginate as a raw material to prepare a new sodium alginate hydrogel material. Sodium alginate is a natural product that is easy to obtain and has good degradability. If it is prepared into a highly water-absorbent hydrogel, its added value can be increased, allowing sodium alginate to be used more widely. Sodium alginate itself has certain water absorption and swelling properties, but due to the influence of its structure, its water absorption is still limited. Graft copolymerization is a very important means of modifying the physical and chemical properties of alginate. Grafting hydrophilic molecules onto the alginate backbone can further enhance the use value of alginate. For example, after grafting hydrophilic molecules onto sodium alginate, a highly water-absorbent gel can be prepared by constructing a three-dimensional network through a cross-linking agent. It is reported that a large number of hydroxyl groups on the alginate backbone can be dehydrogenated to form oxygen free radicals. Therefore, we can use the oxygen free radicals to initiate polymerization to graft acrylic acid onto sodium alginate, and then cross-link the grafted polymer chains through a cross-linking agent to construct a three-dimensional network to obtain a new sodium alginate hydrogel material.

[0042] See Figure 1 and Figure 2 , Figure 1 This application provides a schematic flow chart of an embodiment of a method for preparing a hydrogel. Figure 2 This is a schematic diagram of the preparation process of acrylic acid grafted sodium alginate hydrogel.

[0043] A method for preparing a hydrogel comprises the following steps:

[0044] Step 11: mixing sodium alginate with a free radical initiator, and then adding acrylic acid to react, thereby obtaining sodium alginate grafted with acrylic acid;

[0045] Step 12: Mix and cross-link the sodium alginate grafted with acrylic acid with N,N-methylenebisacrylamide to obtain a hydrogel.

[0046] In this example, an initiator dehydrogenates the hydroxyl groups of sodium alginate to form oxygen free radicals. These oxygen free radicals attract acrylic acid, which is then grafted onto the sodium alginate, forming polyacrylic acid segments on the side chains. N,N-methylenebisacrylamide is then used as a crosslinker to crosslink the grafted polyacrylic acid segments through free radical polymerization to form a highly absorbent hydrogel material. This acrylic acid-grafted sodium alginate hydrogel not only exhibits high water absorption but also exhibits excellent mechanical strength and properties.

[0047] In step S11:

[0048] Natural sodium alginate (SA) is a natural biopolysaccharide produced by a large number of seaweeds. It is a natural anionic linear polysaccharide composed of two basic structural units: 1,4-β,D-mannuronic acid (M) and α-L-guluronic acid (G), arranged in a segmental (-M- or -G-) or alternating (-M-GM-G-) configuration. This structure contains G segments, M segments, and GM (or MG) segments, each formed by G and M being linked individually or alternatingly. The ratio and distribution of M / G segments in sodium alginate are related to the raw seaweed species, harvest season, and location of separation and utilization.

[0049] The free radical initiator may be selected from ammonium persulfate ((NH4)2S2O8).

[0050] The mass ratio of the free radical initiator to the sodium alginate is (1-5):100, specifically 1:100, 1.5:100, 3:100, 5:100, etc., and of course other values within the above range may also be used.

[0051] The mass ratio of the acrylic acid to the sodium alginate is (5-9):1, specifically 5:1, 5.1:1, 6:1, 7:1, 8:1, 8.5:1 or 9:1, etc., and of course other values within the above range may also be used.

[0052] In some embodiments, the step of mixing sodium alginate with a free radical initiator and then adding acrylic acid for mixed reaction to obtain sodium alginate grafted with acrylic acid specifically comprises: heating an aqueous solution of sodium alginate to 65-75° C. in an oxygen-free atmosphere, then adding the free radical initiator, maintaining the temperature at 65-75° C. for a dehydrogenation reaction for 5-15 minutes, then cooling the temperature to 25-35° C., adding acrylic acid, and reacting for 5-10 minutes to obtain sodium alginate grafted with acrylic acid.

[0053] In the above embodiment, the mass volume concentration of sodium alginate in the aqueous solution of sodium alginate is 2-5w / v%, specifically 2-3w / v%, 3-4w / v%, 4-5w / v%, etc., and of course other values within the above range can also be used.

[0054] In a specific embodiment, the free radical initiator is in the form of an aqueous solution, and the mass volume concentration can be (0.01-0.02) g:5 mL, specifically 0.01 g:5 mL, 0.015 g:5 mL, 0.02 g:5 mL, etc., and of course other values within the above range can also be used.

[0055] In a specific embodiment, the acrylic acid is added in the form of an acrylic acid aqueous solution, and the mass volume concentration of the acrylic acid aqueous solution can be (5-10) g:10 mL, specifically 5 g:10 mL, 8 g:10 mL, 10 g:10 mL, etc., and of course other values within the above range can also be used.

[0056] It is understandable that the oxygen-free atmosphere mentioned in this application can be an inert atmosphere such as nitrogen, helium, etc., and specifically, the oxygen-containing atmosphere can be removed by atmosphere replacement.

[0057] In step S12:

[0058] The mass ratio of the N,N-methylenebisacrylamide to the acrylic acid is 0.4% to 2%, and can be specifically selected from 0.4%, 0.8%, 1.2%, 1.6%, 2%, etc., and can also be other values within the above range.

[0059] The mixing and cross-linking of the sodium alginate grafted with acrylic acid and N,N-methylenebisacrylamide specifically comprises: adding N,N-methylenebisacrylamide to the sodium alginate grafted with acrylic acid, and mixing and reacting at 25-35° C. for 20-40 minutes.

[0060] It can be understood that the mixing method can be a combination of one or more methods known in the art, such as stirring and ultrasound.

[0061] In a specific embodiment, the N,N-methylenebisacrylamide is added in the form of an aqueous solution, and the mass volume concentration of the aqueous solution can be (0.01-0.05) g:5 mL, specifically 0.01 g:5 mL, 0.02 g:5 mL, 0.5 g:5 mL, etc., and of course other values within the above range can also be used.

[0062] It can be understood that the water used in the various aqueous solutions mentioned above can specifically be deionized water.

[0063] In some embodiments, after step S12, the method further includes curing at 60-80° C. for 1-3 hours to obtain a cured hydrogel.

[0064] In one embodiment, after the hydrogel is prepared, the method further comprises:

[0065] Step 13: providing a metal ion solution, wherein the metal ion solution comprises one or more metal ions selected from the group consisting of calcium ions, lithium ions, strontium ions, and aluminum ions;

[0066] Step 14: cross-linking the hydrogel with the metal ion solution to obtain a metal ion coordinated hydrogel.

[0067] In this example, the hydrogel preparation process utilizes only the hydroxyl groups of sodium alginate in the graft copolymerization, while retaining its carboxyl groups for coordination. Mixing with a metal ion solution further promotes crosslinking between the carboxyl groups in the hydrogel and the metal ions, forming a double-crosslinked hydrogel. This achieves both high water content and excellent mechanical properties. After ionic crosslinking, the hydrogel's storage modulus and compressive strength are significantly increased, reaching a maximum compressive stress of 1200 kPa, and maintaining and recovering its morphology even after a compression set of 90%.

[0068] When the metal ions include calcium ions, the calcium ion cross-linked metal ion coordination hydrogel can still maintain a certain swelling performance, and the maximum water absorption capacity can still reach 18 times its own weight, that is, a hydrogel with good water absorption and strength is prepared.

[0069] In step 13:

[0070] In some embodiments, the metal ion solution includes an aqueous solution formed by one or more of anhydrous calcium chloride, lithium chloride, strontium chloride hexahydrate, and aluminum chloride hexahydrate.

[0071] In some embodiments, the molar concentration of the metal ions in the metal ion solution is 0.1 to 0.3 Mol / L, specifically 0.1 Mol / L, 0.15 Mol / L, 0.2 Mol / L, 0.3 Mol / L, etc.

[0072] In step 14, in some specific embodiments, cross-linking the hydrogel with the metal ion solution specifically includes: immersing the hydrogel in the metal ion solution and performing the cross-linking reaction for 10 to 15 hours.

[0073] In some embodiments, after step S14, the method further includes: washing with deionized water to remove the system that has not participated in the reaction.

[0074] The present application also provides a hydrogel, which is prepared by the hydrogel preparation method provided in the present application.

[0075] The present application also provides an application of the hydrogel in agriculture, horticulture, desert soil and water moisture retention, gel drive, drug delivery system and water-blocking tape.

[0076] The technical scheme and technical effects of the present application are described in detail below through specific examples and comparative examples. The following examples are only some examples of the present application and are not intended to limit the present application. It is understood that the reagents and materials used in the examples and comparative examples are commercially available products unless otherwise specified.

[0077] Example 1

[0078] Step 1: Prepare a 250mL four-necked flask and equip each of its four openings with a Teflon stirring rod, a nitrogen inlet, a thermometer inlet, and a reflux condenser. Add 50mL of deionized water and 1g of sodium alginate powder to the flask. Place the flask in an oil bath and purge the solution with nitrogen for 30 minutes while stirring to remove oxygen. Stir until the mixture forms a uniform and stable 2 w / v% (weight by volume) sodium alginate solution. Heat the mixture to 70°C.

[0079] Step 2: Add 5 mL of a deionized water solution containing 0.015 g of ammonium persulfate as a free radical initiator to the sodium alginate solution, maintain the temperature at 70°C for 10 minutes, and then cool the reaction system to 30°C.

[0080] Step 3: Then, 10 mL of a mixed solution containing 7 g of acrylic acid (the mass ratio of acrylic acid to sodium alginate is 7:1) was quickly added into the reaction system under stirring and reacted for 5 minutes.

[0081] Step 4: Add 5 mL of an aqueous solution containing 0.02 g of N,N-methylenebisacrylamide and continue stirring for 30 minutes.

[0082] Step 5: After stirring, shape it into a container and then place it in an oven at 70°C to cure for 2 hours.

[0083] Example 2

[0084] This embodiment is substantially the same as embodiment 1, except that 10 mL of a mixed solution containing 5 g of acrylic acid is added in step 3, and the mass ratio of acrylic acid to sodium alginate is 5:1.

[0085] Example 3

[0086] This embodiment is substantially the same as embodiment 1, except that in step 3, 10 mL of a mixed solution containing 6 g of acrylic acid is added, and the mass ratio of acrylic acid to sodium alginate is 6:1.

[0087] Example 4

[0088] This embodiment is substantially the same as embodiment 1, except that 10 mL of a mixed solution containing 8 g of acrylic acid is added in step 3, and the mass ratio of acrylic acid to sodium alginate is 8:1.

[0089] Example 5

[0090] This embodiment is substantially the same as embodiment 1, except that in step 3, 10 mL of a mixed solution containing 9 g of acrylic acid is added, and the mass ratio of acrylic acid to sodium alginate is 9:1.

[0091] Example 6

[0092] This embodiment is substantially the same as embodiment 2, except that 5 mL of an aqueous solution containing 0.04 g of N,N-methylenebisacrylamide is added in step 4.

[0093] Example 7

[0094] This embodiment is substantially the same as embodiment 2, except that 5 mL of an aqueous solution containing 0.06 g of N,N-methylenebisacrylamide is added in step 4.

[0095] Example 8

[0096] This embodiment is substantially the same as embodiment 2, except that 5 mL of an aqueous solution containing 0.08 g of N,N-methylenebisacrylamide is added in step 4.

[0097] Example 9

[0098] This embodiment is substantially the same as embodiment 2, except that 5 mL of an aqueous solution containing 0.10 g of N,N-methylenebisacrylamide is added in step 4.

[0099] Example 10

[0100] This example is essentially the same as Example 1, except that the hydrogel obtained in step 4 is immersed in a 0.2 mol / L calcium ion aqueous solution for crosslinking for 12 hours, followed by rinsing with deionized water to remove any unreacted residues. The metal ions coordinate the hydrogel. The calcium ion aqueous solution is prepared using anhydrous calcium chloride.

[0101] Example 11

[0102] This embodiment is basically the same as embodiment 10, except that a lithium ion aqueous solution prepared with lithium chloride is used instead of a calcium ion aqueous solution.

[0103] Example 12

[0104] This embodiment is substantially the same as embodiment 10, with the only difference being that a strontium ion aqueous solution prepared with strontium chloride hexahydrate is used instead of a calcium ion aqueous solution.

[0105] Example 13

[0106] This embodiment is basically the same as embodiment 10, except that an aluminum ion aqueous solution prepared with aluminum chloride hexahydrate is used instead of a calcium ion aqueous solution.

[0107] Example 14

[0108] This example is essentially the same as Example 2, except that the hydrogel obtained in step 4 is immersed in a 0.2 mol / L calcium ion aqueous solution for crosslinking for 12 hours, followed by rinsing with deionized water to remove any unreacted residues. The metal ions coordinate the hydrogel. The calcium ion aqueous solution is prepared using anhydrous calcium chloride.

[0109] Example 15

[0110] This example is essentially the same as Example 3, except that the hydrogel obtained in step 4 is immersed in a 0.2 mol / L calcium ion aqueous solution for crosslinking for 12 hours, followed by rinsing with deionized water to remove any unreacted residues. The metal ions coordinate the hydrogel. The calcium ion aqueous solution is prepared using anhydrous calcium chloride.

[0111] Example 16

[0112] This example is essentially the same as Example 4, except that the hydrogel obtained in step 4 is immersed in a 0.2 mol / L calcium ion aqueous solution for crosslinking for 12 hours, followed by rinsing with deionized water to remove any unreacted residues. The metal ions coordinate the hydrogel. The calcium ion aqueous solution is prepared using anhydrous calcium chloride.

[0113] Example 17

[0114] This example is essentially the same as Example 5, except that the hydrogel obtained in step 4 is immersed in a 0.2 mol / L calcium ion aqueous solution for crosslinking for 12 hours, followed by rinsing with deionized water to remove any unreacted residues. The metal ions coordinate the hydrogel. The calcium ion aqueous solution is prepared using anhydrous calcium chloride.

[0115] Comparative Example 1

[0116] This comparative example is basically the same as Example 1, except that 10 mL of a mixed solution containing 4 g of acrylic acid is added in step 3.

[0117] Comparative Example 2

[0118] This comparative example is essentially the same as Comparative Example 1, except that the hydrogel obtained in step 4 was immersed in a 0.2 mol / L calcium ion aqueous solution for crosslinking for 12 hours, and then the unreacted system was rinsed with deionized water to allow the metal ions to coordinate the hydrogel. The calcium ion aqueous solution was prepared using anhydrous calcium chloride.

[0119] Infrared spectroscopy was performed on the sodium alginate, acrylic acid and the product after acrylic acid was grafted onto sodium alginate in Example 1. The test results were as follows: Figure 3 The infrared characterization test method is as follows: the test object is washed clean and freeze-dried, and the sample is cut into pieces and tested by KBr pellet. After the hydrogel material is successfully prepared, the changes in the chemical structure of the sample are verified by Fourier transform infrared spectroscopy (FTIR), specifically using the German Bruker VERTEX 70 Fourier infrared spectrometer. After the cleaned hydrogel is freeze-dried, the sample is cut into small pieces and tested by KBr pellet, and the scanning wavenumber range is 4000cm -1 -400cm -1 , with 4cm -1 The resolution of the scan was 32 times to collect all signals. The empty light path background signal was first scanned, and then the infrared absorption characteristic peak of the sample was measured.

[0120] Figure 3 This is the infrared spectrum of acrylic acid before and after grafting onto sodium alginate in Example 1. The infrared spectrum shows that acrylic acid is successfully grafted onto the hydroxyl groups of sodium alginate. -1 The broad absorption peak is the stretching vibration absorption peak of sodium alginate OH, 1590 cm -1 The peak position of asymmetric stretching vibration of carboxylate -COO- group in sodium alginate is 1406cm -1 The characteristic absorption peak at 1298 cm is the CO symmetric stretching vibration absorption peak of the -COO group of sodium alginate. -1 The peak at 1082 cm is attributed to the shear vibration peak of the OH bond in the hydroxyl group of sodium alginate. -1 The stretching vibration peak at 1024 cm is the stretching vibration peak of COC in the molecular structure. This is the stretching vibration peak of COC in sodium alginate. -1 It is the vibration peak of CO of the carbon connected to the hydroxyl group on the ring, which is a characteristic absorption peak in sodium alginate. From the SA-AA-MBA graph after grafting, it can be seen that the new absorption band appears at 1701cm -1 (asymmetric stretching vibration of C=O) is attributed to the stretching vibration of -COOH group in acrylic acid), 1546 cm -1 Assigned to C=O asymmetric stretching vibration (-COO- group), 1448 cm -1 and 1407cm -1 It is attributed to symmetrical stretching vibration (-COO- symmetrical stretching vibration). -1 The peaks around 1163cm -1A new absorption peak appears, which is the stretching vibration absorption peak of the carbon-carbon bond of the six-membered ring of sodium alginate linked to the acrylic acid. These peak positions indicate that acrylic acid has been successfully grafted onto the hydroxyl group of sodium alginate.

[0121] The hydrogels of Example 1 and Examples 10-12 were subjected to scanning electron microscopy (SEM) testing. The test results are shown in FIG. Figures 4 to 8 The specific testing method involved observing the internal morphology of the freeze-dried hydrogel using a Zeiss Ultra 55 (Carl Zeiss, Germany) scanning electron microscope. The hydrogel samples were first thoroughly swollen and rinsed in deionized water, then fractured with liquid nitrogen and freeze-dried in a vacuum chamber to completely remove the water. The dried hydrogel sections were then gold-sprayed and the microscopic morphology of the hydrogels was observed at an accelerating voltage of 20 kV.

[0122] Figures 4 to 8 Electron micrographs of the hydrogels from Examples 1 and 10-12 clearly show the three-dimensional, network-like structure within each hydrogel, with numerous pores evenly distributed throughout the gel and numerous grooves and pores. This cross-linked structure gives the hydrogels a large specific surface area and internal space, enabling them to absorb and hold water efficiently.

[0123] The water absorption rate of the hydrogels of Example 1 and Examples 1-13 was tested. The test results are shown in Figure 9 and Figure 10 And Table 1.

[0124] The test method is as follows: freeze-dry the hydrogel sample to a constant weight, record the mass as M1, immerse it in water for a period of time, quickly remove it, wipe the surface with filter paper to clean the water, and quickly weigh it and record the weight as Mn. The water absorption rate Q is calculated according to formula (1).

[0125]

[0126] Wherein, M1 is the weight of freeze-dried xerogel, unit is g; M n It is the mass of the hydrogel after absorbing water for a certain period of time, in g.

[0127] Figure 9 The graphs are time-water absorption rate graphs of the hydrogels of Comparative Example 1 and Examples 1-5. As can be seen from the graphs, the hydrogels in the graphs all have good water absorption. Among them, the hydrogel of Example 3 (i.e., AA:SA = 6:1) has the highest water absorption capacity, absorbing up to 320 times its own weight in water. The other hydrogels can basically also achieve water absorption capacities of 100 to 200 times their own weight.

[0128] Figure 103 is a time-water absorption rate graph of the hydrogels of Example 2 and Examples 6-9. As can be seen from the graph, the hydrogels of Example 1 and Examples 6-8 all have good water absorption, among which the hydrogel of Example 6 has the relatively largest water absorption capacity.

[0129] The water absorption test results of Examples 10 to 13 are shown in Table 1. As can be seen from Table 1, among Examples 10-13, the gel of Example 11 (lithium ion crosslinking) can achieve a maximum water absorption rate of 3000%, and the gel of Example 13 (aluminum ion crosslinking) has a relatively low water absorption rate, with a maximum water absorption rate of 100%.

[0130] Table 1

[0131] Maximum water absorption Example 10 1600％ Example 11 3000％ Example 12 1400％ Example 13 100％

[0132] Figure 11 The following images illustrate the hydrogels of Comparative Example 1 and Examples 1 through 5. From left to right, these correspond to Comparative Example 1, Examples 1 through 5, respectively. The mass ratio of acrylic acid to sodium alginate (AA:SA) ranges from 4:1 to 9:1. The hydrogel of Comparative Example 1 is soft and barely able to stand upright, whereas the hydrogels of Examples 1-6 stand upright after molding, demonstrating superior mechanical strength.

[0133] Figure 12 The figures show the hydrogels of Examples 1 and 10. It can be seen that compared with Example 1, the mechanical strength of Example 10 is significantly improved after calcium ion coordination and cross-linking.

[0134] Mechanical properties tests were conducted on Examples 10, 14-17 and Comparative Example 1. The test results are shown in Figures 13 to 15 .

[0135] The test method is as follows: the hydrogel is molded into a cylindrical gel with a diameter of 25 mm and a height of 20 mm in a test tube. The mechanical properties of the hydrogel are tested using a compression method. The test is carried out at room temperature (25°C) and the compression speed is fixed at 2 mm / min. Before the test, a thin layer of silicone oil is applied to the surface of the hydrogel to prevent excessive evaporation of water inside the hydrogel during the test. The compressive stress and compressive strain are calculated using formulas (2) and (3).

[0136] The compressive stress is defined as the compressive load divided by the original cross-sectional area of the specimen and is calculated using formula (2).

[0137]

[0138] In formula 2, P is the compressive stress, in Pa; F is the force applied to produce the compressive strain, in N; S is the initial cross-sectional area of the sample, in m 2 .

[0139] The compressive strain is defined as the ratio of the change in the compressed length of the sample to the initial length of the sample. The gel strain is calculated using formula (3).

[0140]

[0141] In formula 3, ε is the compressive strain, in %, ΔL is the change in the compressed length of the sample, in m, and L0 is the initial length of the sample, in m.

[0142] Figure 13 Figure 2 shows the compressive stress-strain curves of the hydrogels of Examples 10, 14-17, and Comparative Example 1. As can be seen, Comparative Example 2 exhibits the lowest stress value at high strain, indicating relatively poor mechanical properties. The hydrogels of Examples 14-17 exhibit relatively respectable stress values at high strain, demonstrating acceptable mechanical properties, strength, and deformation resistance. The hydrogels of Examples 10 and 15 exhibit higher stress values at high strain, indicating good mechanical properties and high strength. The hydrogel of Example 10 exhibits the highest compressive stress, reaching 1200 kPa.

[0143] Figure 14 This is a cyclic compression test graph of the hydrogel of Example 17. The graph shows that this series of hydrogel materials has excellent elasticity, primarily undergoing general elastic deformation with no apparent hysteresis. They can maintain good morphology after repeated compression and exhibit good fatigue resistance.

[0144] Figure 15 This is a compression test diagram of the hydrogel of Example 10. As can be seen from the figure, the gel of Example 10 has good toughness and can still maintain the material morphology after being compressed to 90%. Moreover, due to its good elasticity, it can be compressed repeatedly without damaging the material morphology.

[0145] From the above content, it can be seen that the hydrogel provided in this application is a natural polymer hydrogel material with good water absorption and mechanical properties.

[0146] The hydrogels provided in the examples of the present application, as well as their preparation methods and applications, are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The descriptions of the above embodiments are only intended to help understand the methods and core concepts of the present application. At the same time, for those skilled in the art, according to the concepts of the present application, there may be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present application.

Claims

1. A method for preparing a hydrogel, characterized in that: include: Mixing sodium alginate with a free radical initiator, and then adding acrylic acid to react, thereby obtaining sodium alginate grafted with acrylic acid; The sodium alginate grafted with acrylic acid is mixed and cross-linked with N,N-methylenebisacrylamide to obtain a hydrogel.

2. The preparation method according to claim 1, characterized in that The free radical initiator is selected from ammonium persulfate; and / or, The mass ratio of the free radical initiator to the sodium alginate is (1-5):100; and / or, The mass ratio of the acrylic acid to the sodium alginate is (5-9):1; and / or, The mass ratio of the N,N-methylenebisacrylamide to the acrylic acid is 0.4% to 2%.

3. The preparation method according to claim 2, characterized in that The method of mixing sodium alginate with a free radical initiator and then adding acrylic acid for mixed reaction to obtain sodium alginate grafted with acrylic acid specifically comprises: In an oxygen-free atmosphere, the aqueous solution of sodium alginate is heated to 65-75° C., and then the free radical initiator is added. The temperature is maintained at 65-75° C. for dehydrogenation reaction for 5-15 minutes, and then the temperature is lowered to 25-35° C., acrylic acid is added, and the reaction is carried out for 5-10 minutes to obtain sodium alginate grafted with acrylic acid.

4. The preparation method according to any one of claim 3, characterized in that The mass volume concentration of sodium alginate in the aqueous solution of sodium alginate is 2 to 5 w / v%; and / or, The free radical initiator is in the form of an aqueous solution with a mass volume concentration of (0.01-0.02) g:5 mL; and / or, The acrylic acid is added in the form of an acrylic acid aqueous solution, and the mass volume concentration of the acrylic acid aqueous solution is (5-10) g:10 mL.

5. The preparation method according to claim 4, characterized in that The mixing and cross-linking of the sodium alginate grafted with acrylic acid and N,N-methylenebisacrylamide specifically comprises: adding N,N-methylenebisacrylamide to the sodium alginate grafted with acrylic acid, and mixing and reacting at 25-35° C. for 20-40 minutes.

6. The preparation method according to any one of claims 1 to 5, characterized in that After obtaining the hydrogel, the method further comprises: Providing a metal ion solution, wherein the metal ion solution includes one or more metal ions selected from the group consisting of calcium ions, lithium ions, strontium ions, and aluminum ions; The hydrogel is subjected to a cross-linking reaction with the metal ion solution to obtain a metal ion coordinated hydrogel.

7. The preparation method according to claim 6, characterized in that The metal ion solution includes an aqueous solution formed by one or more of anhydrous calcium chloride, lithium chloride, strontium chloride hexahydrate, and aluminum chloride hexahydrate; and / or, The molar concentration of metal ions in the metal ion solution is 0.1 to 0.3 Mol / L.

8. The preparation method according to claim 7, characterized in that The cross-linking reaction between the hydrogel and the metal ion solution specifically includes: immersing the hydrogel in the metal ion solution and performing the cross-linking reaction for 10 to 15 hours.

9. A hydrogel, characterized in that The invention is prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the hydrogel according to claim 9 in agriculture, horticulture, desert soil and water moisture retention, gel drive, drug delivery system and water-blocking tape.

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