Preparation method of novel biomass hydrogel

Abstract

The invention relates to the technical field of hydrogel preparation, in particular to a preparation method of novel biomass hydrogel. The biomass hydrogel prepared by the invention overcomes the problems of poor hygroscopicity and poor recyclability of traditional hydrogel in a low-humidity environment. The cassava starch is oxidized by sodium periodate to prepare dialdehyde starch, so that the hydrophilicity is enhanced; sodium alginate is coated and combined with an epoxy group to covalently bond and fix lithium chloride, so that salt slow release and low-humidity deliquescence are realized; the ink containing the nano carbon material is introduced, so that efficient photo-thermal conversion is realized; meanwhile, after the substances are subjected to three-dimensional crosslinking, a polymer network-shaped gel structure is formed, and gradient drying and rehydration control are combined, so that the porous structure and the mechanical strength are guaranteed. The prepared hydrogel can quickly absorb moisture and efficiently perform photo-thermal evaporation in a low-humidity environment, and is good in recyclability.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrogel preparation, and specifically to a preparation method of a novel biomass hydrogel. Background Art

[0002] With the increasingly serious global water shortage, the development of new air water intake technologies has become crucial. Traditional air water intake methods usually have high energy consumption or low efficiency in low humidity environments. In recent years, the technology of using hygroscopic materials to absorb moisture in the air and then release the moisture by heating or other means has received extensive attention. As a hydrophilic polymer material with a three-dimensional network structure, hydrogel shows great potential in the field of air water intake due to its high water absorption rate, good flexibility and controllability. Natural polymers such as starch and gelatin are widely sourced, low-cost, and have good biocompatibility and degradability, making them ideal choices for preparing environmentally friendly hydrogels.

[0003] In order to improve the water absorption capacity of hydrogels in low humidity environments, salts with strong hygroscopicity, such as lithium chloride, are usually introduced; lithium chloride can significantly reduce the water vapor pressure at low relative humidity, thus promoting the adsorption of water molecules. In addition, in order to achieve efficient water release, external energy input is usually required. Using photothermal conversion materials to convert solar energy into heat energy to drive the desorption of adsorbed water is an energy-saving and sustainable method. Patent CN114940799B discloses a core-shell structure PAASPNIPAAm hydrogel material for environmental water collection. First, a macroporous core layer material is prepared, and then a small-pore polyacrylate sodium is coated on its surface. After that, polydopamine is coated and finally impregnated in a lithium chloride solution, which solves the problem of poor hygroscopicity in low humidity environments, but its recyclability is poor; Patent CN118063839A discloses a macroporous hydrogel and its preparation method. By using hydroxyethyl cellulose, carboxylated carbon nanotubes and PVA as the main reaction raw materials, and then impregnating in a lithium chloride solution to obtain a macroporous hydrogel, the vacuum freezing time is long and the cost is high; Patent CN119331297A discloses a preparation method of an atmospheric water collection porous gel. The hydrogel prepared according to this method has room for improvement in terms of photothermal interfacial evaporation performance.

[0004] Existing natural polymer-based hydrogels often have problems of insufficient durability during the recycling process, loss of hygroscopic agents leading to a decrease in hygroscopic effect, and insufficient photothermal interfacial evaporation performance, which limits their popularization in practical applications. Therefore, it is of great significance to develop a natural polymer-based hydrogel air water intake material with high hygroscopicity, good photothermal conversion performance and excellent durability.

[0005] For this reason, a preparation method of a novel biomass hydrogel is proposed. Summary of the Invention

[0006] The object of the present invention is to provide a preparation method of a novel biomass hydrogel. By oxidizing cassava starch with sodium periodate to prepare dialdehyde starch, its hydrophilicity is enhanced; sodium alginate is coated and combined with epoxy groups through covalent bonding to immobilize lithium chloride, realizing slow release of salts and deliquescence at low humidity; an ink containing nano-carbon materials is introduced to achieve efficient photothermal conversion; at the same time, after the above substances are three-dimensionally crosslinked, a gel structure in the form of a polymer network is formed, and through gradient drying and rehydration control, the porous structure and mechanical strength are ensured. The prepared hydrogel can rapidly absorb moisture and efficiently perform photothermal evaporation in a low-humidity environment, and has good recyclability.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a preparation method of a novel biomass hydrogel, and the preparation method is as follows:

[0009] S1 Preparation of dialdehyde starch: Cassava starch is oxidized to obtain dialdehyde starch (aldehyde group content ≥ 80%);

[0010] S2 Preparation of starch gel solution: Dialdehyde starch, gelatin, polyacrylic acid and deionized water are mixed, genipin and ammonium carbonate are added, and after reaction, ammonium carbonate is added to obtain a starch gel solution;

[0011] S3 Coating and immobilization: Polyethylene glycol diglycidyl ether is added to lithium chloride, and a sodium alginate solution is added to obtain microspheres;

[0012] S4 Covalent bonding: The microspheres react with the starch gel solution to obtain a gel;

[0013] S5 Functional addition: Ink (containing carbon) is added to the gel;

[0014] S6 Ion cross-linking strengthening: After the ink is added to the gel, it is soaked in a mixed aqueous solution and left to stand at 20 - 30 °C for 1 - 5 h to obtain a gel intermediate;

[0015] S7 Lithium chloride loading and post-treatment: Gradient drying and rehydration control are carried out to obtain a biomass hydrogel.

[0016] Preferably, in S1, the oxidant used for oxidation is sodium periodate; the mass ratio of sodium periodate to cassava starch is 0.2 - 0.6:1; the pH of the oxidation treatment is 2 - 5; the temperature of the oxidation treatment is 35 - 48 °C.

[0017] Preferably, in the process of preparing the starch gel solution in S2, the mass ratio of dialdehyde starch, gelatin, polyacrylic acid, genipin, ammonium carbonate and deionized water is 1 - 2.5:0.8 - 1.8:0.2 - 0.8:0.03 - 0.08:0.07 - 0.11:20.

[0018] Preferably, the specific preparation method of lithium chloride coating and fixation in S3 is as follows: Disperse lithium chloride in absolute ethanol, add polyethylene glycol diglycidyl ether, and stir at 600 rpm for 4 h in a 60 °C water bath to obtain a mixed solution; centrifuge the mixed solution and discard the upper clear liquid; wash the precipitate 3 times with absolute ethanol to remove unreacted raw materials; dry in vacuum at 40 °C for 12 h to obtain epoxy-coated lithium chloride; dissolve sodium alginate in deionized water, heat to 60 °C and stir until completely dissolved to obtain a sodium alginate solution; add the dried epoxy-coated lithium chloride to the sodium alginate solution, continue to stir for 2 h, cool to room temperature, stir and spray dry to form sodium alginate-coated epoxy-coated lithium chloride microspheres, that is, the microspheres are obtained.

[0019] Preferably, the water bath temperature for covalent bonding in S4 is 45 - 58 °C; triethylamine is added during covalent bonding, and the temperature of the second-stage water bath is 40 °C after adding triethylamine.

[0020] Preferably, in the functionalization addition in S5, the volume ratio of the ink to the deionized water in S2 is 0.4 - 1.2:20.

[0021] Preferably, in the ion crosslinking strengthening in S6, the mixed aqueous solution contains 2 wt% calcium chloride and 0.5 wt% glucose.

[0022] Preferably, in the lithium chloride loading and post-treatment in S7, the gradient drying is divided into the first stage, the second stage and the third stage; the drying temperature in the first stage is -20 to -10 °C, and the drying time is 4 - 8 h; the drying temperature in the second stage is -60 to -40 °C, and the drying time is 7.5 - 15 h; the vacuum drying temperature in the third stage is 20 - 30 °C, and the drying time is 2 - 6 h.

[0023] Preferably, the rehydration control in S7 is as follows: The gel obtained by gradient drying is placed in a constant humidity box, the humidity is increased from 30%RH to 60%RH, and finally increased to 90%RH, the humidification speed is 2%RH / min, and the holding time at 30%RH, 60%RH and 90%RH is 1 h each.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. Cassava starch is oxidized to dialdehyde starch, introducing highly polar aldehyde groups, which significantly enhances the hydrophilicity of the material, enabling it to adsorb gaseous water molecules through hydrogen bonding even in low-humidity environments. Combining with the deliquescence characteristics of lithium chloride, sodium alginate coating and epoxy covalent bonding technologies are used to effectively fix salts and achieve a slow-release function, breaking through the moisture absorption bottleneck of traditional materials in low humidity. In addition, the nanocarbon materials in the ink convert solar energy into heat energy through the synergistic effect of light and heat, driving the rapid evaporation and re-adsorption of interfacial water, forming a dynamic moisture absorption-desorption equilibrium; the synergistic design of the three-dimensional interpenetrating cross-linked network (dialdehyde starch-gelatin-polyacrylic acid) cross-linked with calcium ions further optimizes the pore structure, providing continuous capillary transport channels to ensure efficient water adsorption and storage.

[0026] 2. Through covalent cross-linking, ionic cross-linking, and lithium chloride immobilization, the mechanical strength and structural stability of the hydrogel are significantly improved. The covalent network formed by genipin catalysis and the ionic network bonded by calcium ions complement each other, effectively resisting stress fatigue during repeated water absorption and release processes and preventing structural collapse; the lithium chloride microspheres coated with sodium alginate reduce salt loss through the dual effects of chemical bonding and physical barrier, ensuring long-term moisture absorption performance; in terms of process optimization, gradient freeze-drying and staged rehydration control avoid pore damage and rapid swelling, maintaining the porosity and integrity of the material, enabling the hydrogel to still maintain high-efficiency moisture absorption capacity after multiple cycles.

[0027] 3. By introducing nanocarbon materials into the ink, the hydrogel achieves excellent photothermal conversion performance. The nanocarbon efficiently absorbs broad-spectrum solar energy through the surface plasmon resonance effect, converting it into heat energy, significantly increasing the interfacial temperature and driving rapid water evaporation. The hydrophilic aldehyde groups of dialdehyde starch and the deliquescence characteristics of lithium chloride work together to ensure continuous water adsorption in low-humidity environments and direct transport of water through the three-dimensional porous network to the evaporation interface; the cross-linked network not only enhances the thermal stability of the material but also optimizes the heat distribution, reducing energy loss; in addition, the lithium chloride microspheres coated with sodium alginate controllably release hydrated ions under photothermal action, further promoting the dynamic balance of water during evaporation; the synergistic design of these technical means enables the hydrogel to achieve efficient interfacial evaporation driven by solar energy, providing a green and sustainable solution for water resource regeneration in arid regions. Brief Description of the Drawings

[0028] Figure 1 It is a flow chart of the preparation method of the novel biomass hydrogel of the present invention;

[0029] Figure 2 It is a test result diagram of the water contact angle of the novel biomass hydrogel in Example 1 of the present invention;

[0030] Figure 3 It is an infrared thermal imaging diagram of the novel biomass hydrogel in Example 1 of the present invention;

[0031] Figure 4 This is the result graph of the water adsorption characteristics of the novel biomass hydrogel in Example 1 of the present invention and the blank group at RH = 90% / 60% / 30%.

[0032] Figure 5 This is the SEM image of the novel biomass hydrogel after recycling in Comparative Example 8 of the present invention.

[0033] In the figure: a, 30%RH; b, 60%RH; c, 90%RH. Detailed implementation manners

[0034] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0035] Please refer to Figures 1 to 5 , the present invention provides a preparation method of a novel biomass hydrogel, and the technical solution is as follows:

[0036] Example 1

[0037] The preparation method process is as Figure 1 shown, specifically including: S1 Preparation of dialdehyde starch: Take 1 g of cassava starch and 0.4 g of sodium periodate, add 20 mL of deionized water, and stir evenly; Place the mixed solution in a light-proof environment, adjust the pH to 4 with 1% dilute sulfuric acid, and continuously stir at 45 °C for 6 h; After the reaction is completed, centrifuge at 5000 rpm for 10 min through a centrifuge to remove the upper liquid; Wash the precipitate repeatedly with deionized water until neutral; Place the washed precipitate in a freeze dryer and dry at -50 °C for 24 h to obtain white powdery dialdehyde starch;

[0038] S2 Preparation of starch gel solution: Add 1 g of dialdehyde starch, 1 g of gelatin, and 0.5 g of polyacrylic acid (molecular weight 102) to 20 mL of deionized water, and magnetically stir at 400 rpm in a 60 °C constant temperature water bath for 1 h to form a homogeneous solution; Add 0.05 g of genipin and 0.05 g of ammonium carbonate to the solution, keep the water bath at 45 °C, and stir and react at 200 rpm for 2 h. During this period, add a citric acid-sodium citrate buffer to maintain the pH of the system at 6. Add 0.05 g of ammonium carbonate again, stir for 10 min, and then raise the temperature to 60 °C at a rate of 2 °C / min, and stir in the water bath for 0.5 h to form a stable cross-linked network to obtain a starch gel solution;

[0039] S3 Coating and fixing

[0040] Disperse 10 g of lithium chloride with a mesh size of 200 in 50 mL of absolute ethanol, add 1 g of polyethylene glycol diglycidyl ether, and stir at 600 rpm in a water bath at 60 °C for 4 h to obtain a mixed solution, so that the surface of lithium chloride is coated with epoxy groups; centrifuge the mixed solution (5000 rpm, 10 min), discard the supernatant; wash the precipitate with absolute ethanol 3 times to remove unreacted raw materials; dry in vacuum at 40 °C for 12 h to obtain epoxy-coated lithium chloride; dissolve 0.5 g of sodium alginate in 10 mL of deionized water, heat to 60 °C and stir until completely dissolved to obtain a sodium alginate solution; add the dried epoxy-coated lithium chloride to the sodium alginate solution, continue to stir for 2 h, cool to room temperature, stir for 30 min, and spray-dry to form sodium alginate-coated epoxy-coated lithium chloride microspheres;

[0041] S4 Covalent bonding of sodium alginate-coated epoxy-coated lithium chloride microspheres with the gel

[0042] Add 1 g of sodium alginate-coated epoxy-coated lithium chloride microspheres to the above-mentioned starch gel solution, stir at 400 rpm in a water bath at 56 °C for 1 h to cause the epoxy group to undergo a ring-opening reaction with the starch hydroxyl group; add 0.05 g of triethylamine, maintain a water bath at 40 °C, and stir at 200 rpm for 1 h to complete covalent grafting to obtain a gel precursor; then transfer the gel precursor to a square mold with a side length of 2.5 cm;

[0043] S5 Functional addition: Add 0.8 mL of ink and 0.01 g of SDS to the gel precursor, stir at high speed at 600 rpm for 15 min, and then ultrasonically disperse at 20 kHz for 5 min;

[0044] S6 Ion cross-linking strengthening: After adding the ink, soak it in the mixed aqueous solution and let it stand at 25 °C for 2 h to form an ion cross-linking network between Ca² + and the carboxyl group of gelatin to obtain a gel intermediate; the mixed aqueous solution contains 2 wt% calcium chloride and 0.5 wt% glucose, and the balance is water;

[0045] S7 Lithium chloride loading and post-treatment: Freeze-drying: Transfer the gel intermediate to a freeze-dryer and dry it according to a gradient program; First stage: Pre-freeze at -20 °C for 4 h; Second stage: Dry at -50 °C for 12 h; Third stage: Vacuum dry at 25 °C for 4 h to avoid structural collapse; Rehydration control: When in use, place the gel in a constant humidity box and increase the humidity step by step from RH30% to 60%, and finally increase to 90% (1 h for each stage), that is, the initial humidity is 30%RH, after maintaining for 1 h, increase to 60%RH at a rate of 2%RH / min, after maintaining for 1 h, increase to 90%RH at a rate of 2%RH / min, and maintain for 1 h; prevent rapid expansion and rupture.

[0046] Experimental example 1

[0047] The water contact angle of the novel biomass hydrogel prepared in Example 1 was tested, and the test results are as Figure 2 shown;

[0048] The photothermal performance of the novel biomass hydrogel prepared in Example 1 was tested, and the test results are as Figure 3 shown;

[0049] The novel biomass hydrogel prepared in Example 1 and the blank group were tested for water absorption at 30% RH, 60% RH, and 90% RH. The test condition was T = 25 °C, 1000 W / m 2 , and the test results are as Figure 4 shown. The blank group was a novel biomass hydrogel without sodium alginate-coated epoxy-coated lithium chloride microspheres, as shown in Comparative Example 9 below.

[0050] As Figure 2 shown, at 0 s when the water droplet was initially dropped on the novel biomass hydrogel, the water contact angle was 0°. At 200 ms, the water contact angle was 73.4°. At 500 ms, the water contact angle was 57.4°. At 1 s, the water contact angle was 34.6°. At 2 s, the water contact angle was only 16.0°. After only 5 s, the water contact angle became 0°. This indicates that the novel biomass hydrogel of the present invention has good hydrophilicity and good water absorption effect.

[0051] As Figure 3 shown, the novel biomass hydrogel with water storage after light irradiation has a good interfacial light evaporation effect; the infrared thermal imaging results show that after 1 min, 3 min, 5 min, 7 min, 10 min, 15 min, 30 min, 45 min, 60 min, and 90 min of light irradiation, the temperature of the novel biomass hydrogel gradually increased from 35.7 °C to 38.3 °C, 40.2 °C, 42.1 °C, 42.7 °C, 43.0 °C, 44.4 °C, 48.6 °C, 52.0 °C, and 55.6 °C. Under the drive of light, the heat conduction ability inside the novel biomass hydrogel increased, and the interfacial evaporation effect was good. The good water storage and light release effects of the novel biomass hydrogel were achieved.

[0052] As Figure 4 shown, regardless of the relative humidity, the water absorption effect of the blank group was lower than that of the novel biomass hydrogel in Example 1. As the relative humidity decreased, the water absorption amount of the novel biomass hydrogel in Example 1 gradually decreased, but even under the condition of 30% RH, the water absorption amount could still reach 0.9 g / g. This indicates that even under a relatively low relative humidity, the novel biomass hydrogel crosslinked with sodium alginate-coated epoxy-coated lithium chloride microspheres still has good water absorption and water storage effects.

[0053] Example 2-9

[0054] The preparation method of the novel biomass hydrogel in Example 2-9 refers to Example 1, but some parameters are changed, as shown in Table 1. The five substances in Table 1 are dialdehyde starch, gelatin, polyacrylic acid, genipin, and ammonium carbonate added for the second time, respectively, in sequence.

[0055] Table 1 Specific conditions for the preparation method of the novel biomass hydrogel

[0056]

[0057] Comparative Example 1 During the preparation of dialdehyde starch, the dosage of sodium periodate was 1.0 g, and other preparation steps were the same as those in Example 1.

[0058] Comparative Example 2 Cassava starch was not oxidized by sodium periodate, and cassava starch was directly used instead of dialdehyde starch, and other steps were the same as those in Example 1.

[0059] Comparative Example 3 During the preparation of starch gel, dialdehyde starch was not added, and the dosage of gelatin was increased to 2 g, and other preparation steps were the same as those in Example 1.

[0060] Comparative Example 4 During the preparation of starch gel, gelatin was not added, and the dosage of dialdehyde starch was increased to 2 g, and other preparation steps were the same as those in Example 1.

[0061] Comparative Example 5 During the preparation of starch gel, genipin was not added, and other preparation steps were the same as those in Example 1.

[0062] Comparative Example 6 During the preparation of starch gel (ammonium carbonate was not added in segments), 0.1 g of ammonium carbonate and 0.05 g of genipin were added and directly reacted, stirred at 200 rpm for 2.5 h, and during this period, a citric acid-sodium citrate buffer was added to maintain the pH of the system at 6 to form a stable cross-linked network to obtain a starch gel solution; other preparation steps were the same as those in Example 1.

[0063] Comparative Example 7 During the preparation of starch gel (ammonium carbonate was not added in segments), 0.05 g of genipin was added to the solution, maintained at a 40 °C water bath, stirred at 200 rpm for 2 h, then 0.1 g of ammonium carbonate was added, and stirred at a 50 °C water bath for 2 h. During this period, a citric acid-sodium citrate buffer was added to maintain the pH of the system at 6 to form a stable cross-linked network to obtain a starch gel solution; other preparation steps were the same as those in Example 1.

[0064] Comparative Example 8 Lithium chloride was not coated and fixed, and other preparation steps were the same as those in Example 1;

[0065] React lithium chloride directly with the modified starch gel solution, that is, replace the sodium alginate-coated epoxy-coated lithium chloride microspheres in the step of covalently bonding the sodium alginate-coated epoxy-coated lithium chloride microspheres with the gel with lithium chloride. The specific preparation method is as follows: Preparation of dialdehyde starch: Take 1 g of cassava starch and 0.2 - 0.6 g of sodium periodate, add 20 mL of deionized water, and stir evenly; Place the mixture in a light-proof environment, adjust the pH to 2 - 5 with 1% dilute sulfuric acid, and continuously stir at 35 - 48 °C for 6 h; After the reaction, centrifuge at 5000 rpm for 10 min to remove the upper liquid; Wash the precipitate repeatedly with deionized water until neutral; Place the washed precipitate in a freeze dryer and dry at -50 °C for 24 h to obtain white powdery dialdehyde starch; Starch gel: Add 1 g of dialdehyde starch, 1 g of gelatin, and 0.5 g of polyacrylic acid to 20 mL of deionized water, and magnetically stir at 400 rpm in a 60 °C constant temperature water bath for 1 h to form a homogeneous solution; Add 0.05 g of genipin and 0.05 g of ammonium carbonate to the solution, maintain a 40 °C water bath, and stir and react at 200 rpm for 2 h. During this period, add a citric acid-sodium citrate buffer to maintain the pH of the system at 6. Add 0.05 g of ammonium carbonate again and stir in a 50 °C water bath for 0.5 h to dry and form a stable cross-linked network; Functionalization addition: Add 0.8 mL of ink and 0.01 g of SDS to the gel, stir at high speed at 600 rpm for 15 min, and then ultrasonically disperse at 20 kHz for 5 min to ensure uniform dispersion; Ion cross-linking strengthening: Immerse the gel in a mixed aqueous solution and let it stand at 25 °C for 2 h to form an ion cross-linked network with the carboxyl groups of gelatin; The mixed aqueous solution contains 2 wt% calcium chloride and 0.5 wt% glucose, and the balance is water; Lithium chloride loading and post-treatment: Freeze drying: Transfer the gel to a freeze dryer and dry according to a gradient program; First stage: Pre-freeze at -20 °C for 4 h; Second stage: Dry at -50 °C for 12 h; Third stage: Vacuum dry at 25 °C for 4 h to avoid structural collapse; Rehydration control: When in use, place the gel in a constant humidity box and increase the humidity step by step from RH30% to 60%, and finally increase to 90% (1 h for each stage); Other preparation steps are the same as those in Example 1. + Form an ion cross-linked network with the carboxyl groups of gelatin; The mixed aqueous solution contains 2 wt% calcium chloride and 0.5 wt% glucose, and the balance is water; Lithium chloride loading and post-treatment: Freeze drying: Transfer the gel to a freeze dryer and dry according to a gradient program; First stage: Pre-freeze at -20 °C for 4 h; Second stage: Dry at -50 °C for 12 h; Third stage: Vacuum dry at 25 °C for 4 h to avoid structural collapse; Rehydration control: When in use, place the gel in a constant humidity box and increase the humidity step by step from RH30% to 60%, and finally increase to 90% (1 h for each stage); Other preparation steps are the same as those in Example 1.

[0066] Comparative Example 9 Do not add sodium alginate-coated epoxy-coated lithium chloride microspheres (that is, do not contain lithium chloride and any coating components), and other preparation steps are the same as those in Example 1.

[0067] Comparative Example 10 During the covalent bonding of sodium alginate-coated epoxy-coated lithium chloride microspheres with the gel, the water bath stirring temperature is 70 °C.

[0068] Comparative Example 11 During the ion cross-linking strengthening process, do not add glucose, and other preparation methods are the same as those in Example 1.

[0069] Comparative Example 12 During the loading and post-treatment of lithium chloride, only two drying processes were carried out. It was directly dried at -50°C for 12 h, and then vacuum dried at 25°C for 4 h. Other preparation methods and process parameters were the same as those in Example 1.

[0070] Comparative Example 13 The rehydration control process was not carried out, and other preparation methods and process parameters were the same as those in Example 1.

[0071] Comparative Example 14 No ink was added, and other preparation methods were the same as those in Example 1.

[0072] Comparative Example 15 The brand of the ink was replaced with Hero 234A carbon ink, and the ink brand used in Example 1 was M&G Advanced Carbon Ink AICW9001.

[0073] Comparative Example 16 During the ion cross-linking strengthening process, the standing time was 0.5 h, and other preparation methods were the same as those in Example 1.

[0074] Comparative Example 17 During the ion cross-linking strengthening process, the standing time was 10 h, and other preparation methods were the same as those in Example 1.

[0075] Experimental Example 2

[0076] The water absorption of the novel biomass hydrogels prepared in Examples 1-3, Comparative Examples 1-4, and Comparative Examples 6-10 was tested. The results were expressed by the time for complete water absorption. The shorter the absorption time, the better the water absorption effect of the novel biomass hydrogel. And the water collection effect of the novel biomass hydrogel was tested at 90% RH, 60% RH, and 30% RH respectively. The novel biomass hydrogel was a square with a side length of 2.5 cm and a thickness of 0.2 cm. The final test results were expressed as the mass of the absorbed water / mass of the novel biomass hydrogel (g / g). The test results are shown in Table 2.

[0077] Table 2 Test Results of Water Absorption Performance

[0078]

[0079] Under the conditions of Examples 1-3 of the novel biomass hydrogel prepared by the present invention, the time for complete water absorption is 5.0-5.8 s, the water absorption at 90% RH is 4.8-5.3 g / g, the water absorption at 60% RH is 2.1-2.4 g / g, and the water absorption at 30% RH is 0.7-0.9 g / g. Under the conditions of Examples 1-3, starch is first oxidized. Sodium periodate is used as an oxidant to selectively oxidize the C2-C3 hydroxyl groups in cassava starch to generate dialdehyde groups (-CHO), improving hydrophilicity and reactivity. The reaction is carried out in a light-shielded environment to prevent the photolysis failure of sodium periodate, ensuring the efficient progress of the oxidation reaction and maintaining acidic conditions to avoid side reactions such as starch hydrolysis; the aldehyde groups of the formed dialdehyde starch and the amino groups of gelatin form covalent crosslinks through Schiff base reactions, enhancing network stability. The added polyacrylic acid introduces active sites into the crosslinking system. Under the action of genipin, it catalyzes the covalent bonding of aldehyde groups and amino groups. During the preparation of the starch gel, the pore-forming agent ammonium carbonate is added in segments to ensure its complete decomposition, so that the finally obtained novel biomass hydrogel has a moderate specific surface area, improving the water absorption and water storage effects; lithium chloride is double-coated. Polyethylene glycol diglycidyl ether is coated on the surface of lithium chloride, thereby introducing epoxy groups onto the surface of lithium chloride. Then sodium alginate is used for coating, thereby introducing rich epoxy groups and carboxyl groups onto the surface of lithium chloride. During the covalent bonding of the epoxy-coated lithium chloride microspheres coated with sodium alginate and the gel, ink is added to absorb sunlight (visible light-near infrared) through surface plasmon resonance, improving the photothermal conversion efficiency. After adding the ink, ultrasonic treatment is carried out to improve the uniformity of the dispersion of the ink and the system; then it is immersed in a mixed aqueous solution to form ionic bonds with calcium ions, enhancing the mechanical strength of the gel. Glucose is added. On the one hand, it reduces the brittleness caused by calcium ion crosslinking, and on the other hand, it acts as a cryoprotectant to reduce the damage to the novel biomass hydrogel during the subsequent freeze-drying process; then gradient freezing is carried out. The pre-freezing slowly forms ice crystals to avoid the destruction of the porous structure by large ice crystals. Drying sublimates to remove most of the water, retaining the porosity. Three-stage vacuum drying completely removes the residual water to prevent subsequent moisture absorption and collapse; and finally, rehydration control is carried out to avoid the rupture of the gel structure due to rapid water absorption and expansion, ensuring cyclic stability. Through the above treatments, the prepared novel biomass hydrogel has good water absorption efficiency and good water absorption effect at low humidity.

[0080] In Comparative Example 1, due to the excessive amount of oxidant used, the starch chain structure is destroyed by oxidation, the aldehyde groups are unevenly distributed, the water absorption capacity decreases, and the water absorption efficiency decreases; in Comparative Example 2, the cassava starch is oxidized by sodium periodate and contains only hydroxyl groups, and the water absorption effect decreases; in Comparative Example 3, no dialdehyde starch is added, the cross-linking density decreases, and a dense network structure cannot be formed. The strong hydrophilic effect of the aldehyde groups is lacking, and the moisture absorption rate and capacity are both reduced; in Comparative Example 4, no gelatin is added, the cross-linking network is incomplete, the porous structure collapses, the water absorption capacity and moisture absorption rate decrease, but it is better than the effect of Comparative Example 3; in Comparative Example 6, ammonium carbonate is added at one time, the cross-linking reaction is too fast, and the decomposition of ammonium carbonate is incomplete, resulting in uneven pores and water storage capacity. Decreases, and the moisture absorption rate decreases; in Comparative Example 7, ammonium carbonate is added all at once after the addition of genipin is completely reacted. Since the cross-linked network structure has been basically formed during the cross-linking process, the added porogen cannot exert a good porogen effect; Comparative Example 8 is not coated and fixed, lithium chloride is not cross-linked with the modified starch gel solution, the water absorption amount is slightly reduced, and the moisture absorption efficiency is increased compared with Example 1; Comparative Example 9 does not add sodium alginate-coated epoxy-coated lithium chloride microspheres, and only relies on dialdehyde starch and gelatin for moisture absorption, and the moisture absorption rate and water absorption are greatly reduced; Comparative Example 10 The water bath stirring temperature is high, the dialdehyde starch part produces gelatinization, the cross-linking effect is reduced, and the moisture absorption rate and water absorption are reduced compared with Example 1.

[0081] Experimental Example 3

[0082] The water absorption capacity of the novel biomass hydrogel after cyclic use was tested. The novel biomass hydrogels obtained in Example 1, Examples 4-6, Comparative Example 5, and Comparative Examples 8-13 were tested for water collection under 30% RH conditions, as well as water collection performance under 30% RH after 20 cycles of use. The test results are shown in Table 3.

[0083] Table 3 Water collection performance test for recycling

[0084]

[0085] The novel biomass hydrogel prepared by the present invention has good recycling performance. Under the conditions of Example 1 and Examples 4-6, the water absorption at 30%RH is 0.8-1.2g / g. After 30 cycles, the water absorption at 30%RH is 0.66-1.03g / g, and the percentage of water absorption decrease is 10%-14%, which is better than the comparative example group. During the preparation of the starch gel of Comparative Example 5, no genipin is added for cross-linking, and the network structure of the hydrogel is loose. After the cycle, the structure collapses and the water absorption drops sharply. Comparative Example 8 does not carry out coating and fixation, and directly reacts lithium chloride with the modified starch gel solution. After 30 cycles, since it does not contain cross-linked groups, after repeated water absorption and release, there is a significant loss of lithium chloride, which ultimately leads to a significant decrease in the water absorption of the novel biomass hydrogel. Figure 5From the SEM results, it can be found that after cycling, the content of lithium chloride loaded on the surface of the novel biomass hydrogel is extremely low, and there are depressions on the surface of the novel biomass hydrogel after the loss of lithium chloride; in Comparative Example 9, the epoxy-coated lithium chloride microspheres without sodium alginate coating are added, and the water absorption effect is significantly reduced at a low air humidity of 30%, and after 30 cycles, the water absorption amount is significantly reduced at a low air humidity; in Comparative Example 10, the temperature during the covalent bonding process is too high, resulting in partial chemical denaturation of the novel biomass hydrogel, and the water absorption amount at a low water content and the water absorption amount after cycling are reduced; in Comparative Example 11, glucose is not added, the brittleness of calcium ion crosslinking increases, and on the other hand, the protective effect during the freezing process cannot be exerted, ultimately resulting in a decrease in its water absorption and water absorption after cycling; in Comparative Example 12, the three-stage gradient drying process is not carried out, resulting in the destruction of the pore structure by ice crystals, and the water absorption amount decreases after cycling; in Comparative Example 13, during the rehydration control process, rapid water absorption and swelling lead to gel rupture and poor structural stability, and its water absorption amount is greatly reduced after cycling.

[0086] Experimental Example 4

[0087] The novel biomass hydrogels prepared in Example 1, Examples 7-9, and Comparative Examples 14-17 were subjected to an evaporation experiment. According to GB / T 35237-2017 "Test Method for Absorptivity of Solar Photothermal Materials", the surface temperature change was recorded by an infrared thermal imager, and the evaporation rate was calculated by combining the mass loss. The evaporation rate = Δm / A·t, where Δm is the mass loss (kg), A is the gel surface area (m²), and t is the illumination time (h); the test results are shown in Table 4.

[0088] Table 4 Test Results of Interfacial Evaporation Rate

[0089]

[0090] For the novel biomass hydrogel prepared by the present invention, the evaporation rate under the conditions of Example 1 and Examples 7-9 is 1.76-2.01 Kg / m 2 ·h. By creatively adding ink to the novel biomass hydrogel, the nano-carbon contained therein absorbs a broad spectrum (visible light-near infrared) through the surface plasmon resonance effect, increasing the light absorption rate, driving the interface temperature to rise, and accelerating the interface evaporation process. The aldehyde groups of dialdehyde starch form strong hydrogen bonds with water molecules, enhancing the hydrophilicity and adsorption capacity. The lithium chloride microspheres coated with sodium alginate adsorb gaseous water through deliquescence at low humidity and release Li + ·nH 2O hydrated ions enhance water transport. Dialdehyde starch crosslinks with gelatin and genipin to form a three-dimensional network, and finally bonds with calcium ions to improve mechanical stability. The novel biomass hydrogel has good photointerface evaporation effect. In Comparative Example 14, no ink was added, lacking nano-carbon light absorption, resulting in a 60% decrease in the photothermal conversion efficiency and a sharp drop in the evaporation rate; in Comparative Example 15, the ink brand used was Hero 234A carbon ink. Due to the relatively low carbon content and larger particle size compared with Example 1, the light absorption rate decreased and the evaporation rate dropped; in Comparative Example 16, the ion crosslinking standing time was too short, the calcium ion crosslinking was insufficient, the network was loose, and the water transport efficiency decreased; in Comparative Example 17, the ion crosslinking standing time was too long, over-crosslinking led to a decrease in porosity and an increase in the water evaporation resistance, so the evaporation rate decreased.

[0091] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a novel biomass hydrogel, characterized in that: The preparation method is as follows: S1 preparation of dialdehyde starch: oxidizing cassava starch to obtain the dialdehyde starch; Preparation of S2 starch gel solution: mixing the dialdehyde starch, gelatin, polyacrylic acid and deionized water, adding genipin and ammonium carbonate, and adding the ammonium carbonate after the reaction to obtain the starch gel solution; S3 coating and fixation: adding polyethylene glycol diglycidyl ether to lithium chloride and adding sodium alginate solution to obtain microspheres; S4 covalent bonding: the microspheres react with the starch gel solution to obtain a gel; S5 functionalization addition: adding ink to the gel; S6 ion cross-linking strengthening: the gel is added to the ink and immersed in a mixed aqueous solution, and allowed to stand at 20-30° C. for 1-5 hours to obtain a gel intermediate; S7 lithium chloride loading and post-treatment: gradient drying and rehydration control to obtain the biomass hydrogel.

2. The method for preparing a novel biomass hydrogel according to claim 1, characterized in that: The oxidant used in the oxidation in S1 is sodium periodate; the mass ratio of the sodium periodate to the cassava starch is 0.2-0.6:1; the pH of the oxidation treatment is 2-5; and the temperature of the oxidation treatment is 35-48°C.

3. The method for preparing a novel biomass hydrogel according to claim 1, characterized in that: S2 During the preparation of the starch gel solution, the mass ratio of the dialdehyde starch, the gelatin, the polyacrylic acid, the genipin, the ammonium carbonate and the deionized water is 1-2.5: 0.8-1.8: 0.2-0.8: 0.03-0.08: 0.07-0.11:

20.

4. The method for preparing a novel biomass hydrogel according to claim 1, characterized in that: The specific preparation method of lithium chloride coating and fixation in S3 is as follows: disperse lithium chloride in anhydrous ethanol, add polyethylene glycol diglycidyl ether, stir at 600 rpm for 4 hours in a 60°C water bath to obtain a mixed solution; centrifuge the mixed solution and discard the supernatant; wash the precipitate with the anhydrous ethanol for 3 times to remove unreacted raw materials; vacuum dry at 40°C for 12 hours to obtain epoxy-coated lithium chloride; take sodium alginate and dissolve it in the deionized water, heat to 60°C and stir until it is completely dissolved to obtain the sodium alginate solution; add the dried epoxy-coated lithium chloride to the sodium alginate solution, continue stirring for 2 hours, cool to room temperature, stir and spray dry to form sodium alginate-coated epoxy-coated lithium chloride microspheres, that is, the microspheres are obtained.

5. The method for preparing a novel biomass hydrogel according to claim 1, characterized in that: The water bath temperature of S4 covalent bonding is 45-58°C; triethylamine is added during covalent bonding, and the temperature of the second water bath after adding triethylamine is 40°C.

6. The method for preparing a novel biomass hydrogel according to claim 1, characterized in that: The volume ratio of the ink in the functional addition in S5 to the deionized water in S2 is 0.4-1.2:

20.

7. The method for preparing a novel biomass hydrogel according to claim 1, characterized in that: In the ionic crosslinking strengthening described in S6, the mixed aqueous solution contains 2wt% calcium chloride and 0.5wt% glucose.

8. The method for preparing a novel biomass hydrogel according to claim 1, characterized in that: In the lithium chloride loading and post-treatment of S7, the gradient drying is divided into the first stage, the second stage and the third stage; the drying temperature of the first stage is -20 to -10°C, and the drying time is 4-8h; the drying temperature of the second stage is -60 to -40°C, and the drying time is 7.5-15h; the vacuum drying temperature of the third stage is 20-30°C, and the drying time is 2-6h.

9. The method for preparing a novel biomass hydrogel according to claim 1, characterized in that: The rehydration control in S7 is as follows: the gel obtained by gradient drying is placed in a constant humidity chamber, and the humidity is increased from 30% RH to 60% RH, and finally to 90% RH, the humidification rate is 2% RH / min, and the holding time at 30% RH, 60% RH and 90% RH is 1 hour.

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