A biomass-based air harvesting hydrogel and a method of preparing the same

Abstract

The application belongs to the field of functional polymer materials, and provides a preparation method of biomass-based air water collection hydrogel, which comprises the following steps: in an anaerobic environment, N-isopropyl acrylamide is added to a sodium lignin carboxylate solution, an initiator is further added, and a grafting modification reaction is carried out by heating; after the reaction is completed, the reaction solution is collected, cooled, diluted, anhydrous ethanol is added, stirring is performed until the solution is turbid, solid-liquid separation is performed, the precipitate is collected, and washing is performed to obtain NIPAAm-sodium lignin carboxylate; the NIPAAm-sodium lignin carboxylate, hydroxypropyl cellulose, sodium alginate and water are uniformly mixed, poured into a mold, a calcium salt solution is sprayed on the surface, and reaction is performed to obtain a hydrogel. The application forms a high-strength light-sensitive and temperature-sensitive double-response gel material with a triple network structure by integrating hydroxypropyl cellulose (HPC), modified lignin and sodium alginate; the gel absorbs water at low temperature in the absence of light, the gel dehydrates at high temperature in the presence of light, and the gel has the characteristics of efficient water absorption and controllable dehydration.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of functional polymer materials, and particularly relates to a biomass-based air water collection hydrogel and a preparation method thereof. BACKGROUND

[0002] The information disclosed in this BACKGROUND section is only for the purpose of increasing the understanding of the general background of the present application and should not be taken as an acknowledgement or any form of suggestion that this information forms prior art with respect to any patentable matter disclosed herein.

[0003] The total water on earth is only 2.5%, of which less than 0.36% is liquid fresh water that can be directly used, and about 30% of the land area is arid (annual average humidity RH < 20%). Although the research and development of existing adsorption type air water collection technology is aimed at arid areas, it still faces serious bottleneck problems: first, the adsorption / desorption kinetics of most hygroscopic materials is slow (performance decay > 50% when RH < 30%), and the structure is easy to disintegrate due to swelling stress in the cycle; second, the main intermittent adsorption-desorption device causes efficiency loss due to discontinuous operation, and the design and manufacture of continuous integrated equipment still lack universal solutions, which restricts the application of the technology on a large scale. SUMMARY

[0004] In order to solve the above problems, the present application provides a biomass-based air water collection hydrogel and a preparation method thereof. The present application forms a high-strength light-sensitive and temperature-sensitive double-response gel material with a triple network structure by integrating hydroxypropyl cellulose (HPC), modified lignin and sodium alginate. The gel material has the characteristics of efficient water absorption and controllable dehydration, that is, it absorbs water at low temperature in the absence of light and dehydrates at high temperature in the presence of light.

[0005] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0006] In a first aspect of the present application, a preparation method of a biomass-based air water collection hydrogel is provided, comprising:

[0007] In an oxygen-free environment, N-isopropyl acrylamide is added to a sodium lignin carboxylate solution, and then an initiator is added. The grafting modification reaction is carried out by heating. After the reaction is completed, the reaction solution is collected, cooled, diluted, and then anhydrous ethanol is added. The solution is stirred until it becomes turbid. The solid-liquid separation is carried out, and the precipitate is collected and washed to obtain NIPAAm-sodium lignin carboxylate.

[0008] The NIPAAm-sodium lignin carboxylate, hydroxypropyl cellulose, sodium alginate and water are uniformly mixed, poured into a mold, and a calcium salt solution is sprayed on the surface. The reaction is carried out. After the reaction is completed, freeze-drying is carried out to obtain the biomass-based air water collection hydrogel.

[0009] The present application constructs a high-strength temperature-sensitive air water-trapping hydrogel material with a triple network structure by integrating hydroxypropyl cellulose, NIPAAm-lignin sodium carboxylate and sodium alginate. The triple network structure ensures the high strength and durability of the air water-trapping hydrogel. Hydroxypropyl cellulose, NIPAAm-lignin sodium carboxylate, sodium alginate and calcium chloride are all low-toxicity or non-toxic and have strong water absorption performance, ensuring that the prepared air water-trapping hydrogel material has good water absorption capacity, thereby avoiding the use of toxic hygroscopic substances such as lithium chloride in the air water-trapping hydrogel. The use of lignin gives the air water-trapping hydrogel good photothermal properties. The presence of hydroxypropyl cellulose and NIPAAm enables the air water-trapping hydrogel to absorb water at low temperature (< 35 DEG C) without light and to dehydrate at high temperature (> 45 DEG C) with light, giving the air water-trapping hydrogel controllable dehydration properties. Therefore, the air water-trapping hydrogel prepared by the present application is non-toxic, high-strength, high-water-absorbing and controllable in dehydration, and is an excellent air water-trapping hydrogel material.

[0010] In some embodiments, the lignin sodium carboxylate is prepared from purified lignin, and the preparation method of the purified lignin comprises:

[0011] The kraft black liquor is diluted with water, filtered to obtain a preliminarily purified black liquor, which is dispersed by stirring, and a dilute acid solution is added to precipitate lignin, which is washed and purified to obtain purified lignin.

[0012] In some embodiments, the concentration of the kraft black liquor after dilution is 5-10% (w / v).

[0013] In some embodiments, the dilute acid solution is added to adjust the pH value of the black liquor to 3-4 (near the isoelectric point of lignin, at which the precipitation amount is the largest).

[0014] In some embodiments, the preparation method of the lignin sodium carboxylate comprises: making the purified lignin alkaline by adding alkali, adding chloroacetic acid, and performing grafting reaction by heating; after the reaction is completed, the reaction solution is cooled, diluted, and the pH value is adjusted, anhydrous ethanol is added, stirring is performed until the solution is turbid, solid-liquid separation is performed, and the precipitate is collected; the precipitate is washed to obtain lignin sodium carboxylate.

[0015] In some embodiments, the pH value of the purified lignin is adjusted to 12-13 by adding alkali.

[0016] In some embodiments, the mass ratio of lignin to chloroacetic acid is 1:2-1:4.

[0017] In some embodiments, the temperature of the grafting reaction is 60-70 DEG C, and the reaction time is 4-6 hours.

[0018] In some embodiments, after the grafting reaction is completed, the pH value of the reaction solution is adjusted to 3-4 (using dilute acid); the volume ratio of the reaction solution to anhydrous ethanol is 1:0.5-1:2.

[0019] In some embodiments, the ratio of the amount of the sodium lignin carboxylate to the amount of N-isopropyl acrylamide is 1:3-1:5;

[0020] In some embodiments, the initiator is ammonium persulfate;

[0021] In some embodiments, the amount of the initiator is 0.5-2.5wt% of the total mass of the sodium lignin carboxylate and the N-isopropyl acrylamide.

[0022] In some embodiments, the volume ratio of the reaction solution to anhydrous ethanol is 1:0.5-1:2.

[0023] In some embodiments, the mass ratio of the NIPAAm-sodium lignin carboxylate, hydroxypropyl cellulose, and sodium alginate is 4-9:1-3:2-6.

[0024] In some embodiments, the concentration of the calcium salt solution is 3-6wt%.

[0025] More specifically, the method comprises:

[0026] (1) The sulfate pulp black liquor is diluted with deionized water, filtered to obtain the black liquor after preliminary purification. The black liquor is stirred and dispersed, and a certain amount of dilute acid solution is added dropwise to precipitate the lignin, which is washed and purified to obtain the purified lignin.

[0027] (2) The purified lignin is adjusted to alkaline with sodium hydroxide, chloroacetic acid is added, and the grafting reaction is carried out under heating. After the reaction is completed, the reaction solution is cooled, diluted, and the pH value is adjusted. Anhydrous ethanol is added, stirred until the solution is turbid, and centrifuged to precipitate. The precipitate is washed with ethanol-water mixture multiple times to obtain pure sodium lignin carboxylate.

[0028] (3) The sodium lignin carboxylate is diluted and stirred to completely dissolve under heating. Nitrogen is introduced to create an anaerobic environment, and then N-isopropyl acrylamide NIPAAm is added and stirred to completely dissolve. APS solution is added dropwise to activate the reaction system, and the grafting modification reaction is carried out under heating. After the reaction is completed, the reaction solution is cooled, diluted, and anhydrous ethanol is added. Stirring is performed until the solution is turbid, and centrifugation is performed to precipitate. The precipitate is washed with ethanol-water mixture multiple times to obtain pure NIPAAm-sodium lignin carboxylate.

[0029] (4) The NIPAAm-sodium lignin carboxylate, hydroxypropyl cellulose, and sodium alginate are thoroughly mixed, poured into a specific mold, and sprayed with a calcium chloride solution on the surface. After stabilization for a period of time, freeze-drying is performed to obtain an air water collection gel material.

[0030] In a second aspect, the present application provides a biomass-based air harvesting hydrogel prepared by the above method.

[0031] In a third aspect, the present application provides the use of the above biomass-based air harvesting hydrogel in the preparation of an air harvester.

[0032] Advantages of the present application

[0033] (1) Structural innovation and mechanical performance improvement: By innovatively integrating hydroxypropyl cellulose, NIPAAm-sodium lignin carboxylate and sodium alginate, a triple network structure is successfully constructed, significantly improving the mechanical strength and durability of the air harvesting hydrogel material. This unique structural design enables the material to maintain good structural integrity during long-term use.

[0034] (2) Environmental friendliness and safety: The main components of the material, including hydroxypropyl cellulose, NIPAAm-sodium lignin carboxylate, sodium alginate and calcium chloride, all have low toxicity, non-toxicity and strong water absorption performance, effectively avoiding the use of toxic and hygroscopic substances such as lithium chloride in traditional air harvesting materials, greatly improving the environmental friendliness and safety of the material.

[0035] (3) Photothermal properties and intelligent control: By introducing lignin components, the material is endowed with good light-heat conversion properties. Combined with the temperature response characteristics of hydroxypropyl cellulose and NIPAAm, the material can efficiently absorb water under non-light conditions (<35℃), and achieve controlled dehydration under light conditions (>45℃), realizing intelligent control of the harvesting process.

[0036] (4) Excellent comprehensive performance: The air harvesting hydrogel material prepared by the present application integrates non-toxicity, high strength, high water absorption and controllable dehydration, overcoming the shortcomings of traditional air harvesting materials in safety, durability and controllability, and is an air harvesting hydrogel material with excellent performance.

[0037] Through the above innovative design, the present application not only solves the technical bottlenecks of traditional air harvesting materials, but also provides a new type of efficient, safe and reliable material solution for the air harvesting field, with significant technical progress and practical application value. DETAILED DESCRIPTION

[0038] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used in the present application have the same meaning as generally understood by those skilled in the art to which the present application belongs.

[0039] The application will be further described in detail below with reference to specific examples, it should be pointed out that the specific examples are an explanation of the application rather than a limitation.

[0040] In the following examples, the kraft black liquor is taken from a broad-leaf wood kraft pulp production line of a factory in Shandong.

[0041] Example 1

[0042] (1) The kraft black liquor with a concentration of 8% is filtered using a 0.45 μm microporous filter membrane, the filtrate is collected and continuously stirred, and 5% concentrated hydrochloric acid is added dropwise therein until the pH value of the black liquor is reduced to about 3.5. It is filtered using a 0.45 μm microporous filter membrane and washed with deionized water to obtain pure lignin particles.

[0043] (2) 5 g (absolute dry mass) of lignin particles are taken and added to 50 ml of sodium hydroxide solution with a pH of 12-13, 15 g of chloroacetic acid is added, the water bath is warmed to 65°C, and the reaction is continuously stirred for 5 hours. After the reaction is completed and cooled, 150 ml of deionized water is added and the pH is adjusted to 3-4 with dilute hydrochloric acid, 200 ml of ethanol is added, stirred until the solution is turbid, and the modified lignin precipitate is centrifuged. The precipitate is washed with 70% ethanol water solution for 3 times to obtain pure lignin carboxylate sodium.

[0044] (3) 5 grams (absolute dry mass) of lignin carboxylate sodium are dispersed in 400 milliliters of deionized water, stirred at 60°C until completely dissolved, and then nitrogen is introduced for 30 minutes to continuously bubble to remove oxygen in the system. Under nitrogen protection, 20 grams of NIPAAm is added and stirred until completely dissolved. Then 0.25 grams of APS is dissolved in 5 milliliters of deionized water and added dropwise into the reaction system within 10 minutes. The reaction system is warmed to 70°C and reacted at constant temperature for 8 hours. After the reaction is completed, the system is cooled, 400 milliliters of ethanol is added and stirred until the solution becomes turbid, and then centrifuged to separate the modified lignin precipitate. Finally, the precipitate is washed with 70% ethanol water solution for 3 times to obtain pure NIPAAm-lignin carboxylate sodium.

[0045] (4) 6 grams (absolute dry mass) of NIPAAm-lignin carboxylate sodium, 2.5 grams of hydroxypropyl cellulose, and 4 grams of sodium alginate are mixed, deionized water is added to a total weight of 100 g, and stirred and mixed uniformly, then 5 ml of 5% calcium chloride solution is uniformly sprayed on the surface. After standing for 2 hours, freeze-drying is performed to obtain an air water harvesting hydrogel in the form of a film.

[0046] The film-shaped air water harvesting hydrogel prepared in this example has a thickness of about 0.4 cm and a maximum water harvesting capacity per hour of 19.75 g (158%) in a humidity of 30% atmospheric environment. Under direct sunlight at noon in autumn, 17.76 g of water can be desorbed and collected within 30 minutes.

[0047] Example 2

[0048] (1) The kraft black liquor with a concentration of 8% was filtered using a 0.45 μm microporous filter membrane, the filtrate was collected and continuously stirred, and 5% dilute hydrochloric acid was added dropwise until the pH of the black liquor decreased to about 3.5. It was filtered using a 0.45 μm microporous filter membrane and washed with deionized water to obtain pure lignin particles.

[0049] (2) 5 g (absolute dry mass) of lignin particles were taken and added to 50 ml of a sodium hydroxide solution with a pH of 12-13, 15 g of chloroacetic acid was added, the water bath was heated to 60°C, and the reaction was continuously stirred for 6 hours. After the reaction was completed and cooled, 150 ml of deionized water was added and the pH was adjusted to 3-4 with dilute hydrochloric acid, 200 ml of ethanol was added, stirred until the solution was turbid, and centrifuged to obtain a modified lignin precipitate. The precipitate was washed 3 times with 70% ethanol aqueous solution by centrifugation to obtain pure lignin carboxylate sodium.

[0050] (3) 5 grams (absolute dry mass) of lignin carboxylate sodium were dispersed in 400 milliliters of deionized water and stirred at 60°C until completely dissolved, then nitrogen was bubbled for 30 minutes to continuously remove oxygen from the system. Under nitrogen protection, 20 grams of NIPAAm was added and stirred until completely dissolved. Then 0.25 grams of APS was dissolved in 5 milliliters of deionized water and added dropwise to the reaction system within 10 minutes. The reaction system was heated to 70°C and reacted at constant temperature for 8 hours. After the reaction was completed, the system was cooled, 400 milliliters of ethanol was added and stirred until the solution became turbid, then centrifuged to obtain a modified lignin precipitate. Finally, the precipitate was washed 3 times with 70% ethanol aqueous solution by centrifugation to obtain pure NIPAAm-lignin carboxylate sodium.

[0051] (4) 4 grams (absolute dry mass) of NIPAAm-lignin carboxylate sodium, 2.5 grams of hydroxypropyl cellulose, and 4 grams of sodium alginate were mixed, then deionized water was added to a total weight of 100 g, and stirred and mixed uniformly. Then 5 ml of a 5% calcium chloride solution was uniformly sprayed on the surface. After standing for 2 hours, it was freeze-dried into an air water harvesting hydrogel.

[0052] The film-shaped air water harvesting hydrogel prepared in this example with a thickness of about 0.4 cm has a maximum water harvesting capacity of 16.5 g (143%) per unit hour in an atmosphere with a humidity of 30%. Under direct sunlight at noon in autumn, it can desorb and collect 14.6 g of water within 30 minutes.

[0053] Example 3

[0054] (1) The kraft black liquor with a concentration of 8% was filtered using a 0.45 μm microporous filter membrane, and the filtrate was collected and continuously stirred, and 5% dilute hydrochloric acid was added dropwise until the pH of the black liquor was reduced to about 3.5. It was filtered using a 0.45 μm microporous filter membrane and washed with deionized water to obtain pure lignin particles.

[0055] (2) 5 g (absolute dry mass) of lignin particles were taken and added to 50 ml of a sodium hydroxide solution with a pH of 12-13, 15 g of chloroacetic acid was added, and the water bath was heated to 70°C, and the reaction was continuously stirred for 4 hours. After the reaction was completed and cooled, 150 ml of deionized water was added and the pH was adjusted to 3-4 with dilute hydrochloric acid, 200 ml of ethanol was added, and the solution was stirred until it became turbid, and the modified lignin precipitate was centrifuged. The precipitate was washed 3 times with 70% ethanol aqueous solution by centrifugation to obtain pure lignin carboxylate sodium.

[0056] (3) 5 grams (absolute dry mass) of lignin carboxylate sodium were dispersed in 400 milliliters of deionized water and stirred at 60°C until completely dissolved, then nitrogen was introduced for 30 minutes to continuously bubble to remove oxygen in the system. Under nitrogen protection, 20 grams of NIPAAm was added and stirred until completely dissolved. Then 0.25 grams of APS was dissolved in 5 milliliters of deionized water and added dropwise to the reaction system within 10 minutes. The reaction system was heated to 70°C and reacted at constant temperature for 8 hours. After the reaction was completed, the system was cooled, 400 milliliters of ethanol was added and stirred until the solution became turbid, then centrifuged to obtain the modified lignin precipitate. Finally, the precipitate was washed 3 times with 70% ethanol aqueous solution by centrifugation to obtain pure NIPAAm-lignin carboxylate sodium.

[0057] (4) 9 grams (absolute dry mass) of NIPAAm-lignin carboxylate sodium, 2.5 grams of hydroxypropyl cellulose, and 4 grams of sodium alginate were mixed, then deionized water was added to a total weight of 100 g, and stirred to mix uniformly, then 5 ml of a 5% calcium chloride solution was uniformly sprayed on the surface. After standing for 2 hours, freeze-drying was performed to obtain an air water harvesting hydrogel.

[0058] The film-shaped air water harvesting hydrogel prepared in this example with a thickness of about 0.4 cm has a maximum water harvesting capacity of 21.3 g (1.52%) per unit hour in an atmosphere with a humidity of 30%. Under direct sunlight at noon in autumn, 20.21 g of water can be collected within 30 minutes.

[0059] Comparative Example 1

[0060] The difference from Example 1 is that in step (4), no hydroxypropyl cellulose is added.

[0061] The air water harvesting hydrogel prepared in this example has poor strength and is not suitable for air water harvesting and water desorption.

[0062] Comparative Example 2

[0063] The difference from Example 2 is that in step (4), NIPAAm-lignin carboxylate sodium is not added.

[0064] The air water collection hydrogel prepared in this example has a maximum water collection capacity of 3.05 g (29.9%) per hour in an atmosphere with a humidity of 30%. Under direct sunlight at noon in autumn, 1.72 g of water can be collected within 30 minutes.

[0065] Comparative Example 3

[0066] The difference from Example 2 is that in step (4), NIPAAm-lignin carboxylate sodium is not added.

[0067] The air water collection hydrogel prepared in this example has a maximum water collection capacity of 14.62 g (131%) per hour in an atmosphere with a humidity of 30%. Under direct sunlight at noon in autumn, 7.25 g of water can be collected within 30 minutes, and the aggregation strength is significantly poorer, and the hydrogel cannot be reused multiple times.

[0068] Comparative Example 4

[0069] The difference from Example 2 is that steps (1) and (2) are omitted, and in step (3), sodium carboxylate is used instead of lignin carboxylate sodium to prepare NIPAAm-sodium carboxylate.

[0070] The air water collection hydrogel prepared in this example has a maximum water collection capacity of 2.8 g (23.3%) per hour in an atmosphere with a humidity of 30%. Under direct sunlight at noon in autumn, 1.23 g of water can be collected within 30 minutes.

[0071] From the comparison of Example 2 and Comparative Example 2, it can be seen that the addition of NIPAAm-lignin carboxylate sodium significantly improves the water absorption capacity and controllable dehydration capacity of the air water collection hydrogel.

[0072] From the comparison of Example 2 and Comparative Examples 3 and 4, it can be seen that the absence of NIPAAm or lignin units significantly reduces the water absorption and controllable dehydration capacity of the air water collection hydrogel.

[0073] The above only describes preferred embodiments of the present application and is not intended to limit the present application. Those skilled in the art can make various modifications and changes to the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a biomass-based air-collecting hydrogel, characterized in that, include: In an anaerobic environment, N-isopropylacrylamide was added to a sodium lignin carboxylate solution, followed by an initiator. The temperature was raised to carry out a grafting modification reaction. After the reaction was completed, the reaction solution was collected, cooled, diluted, and anhydrous ethanol was added. The solution was stirred until it became turbid. Solid-liquid separation was performed, the precipitate was collected, washed, and NIPAAm-sodium lignin carboxylate was obtained. The NIPAAm-lignin carboxylate sodium, hydroxypropyl cellulose, and sodium alginate are mixed evenly, poured into a mold, and a calcium salt solution is sprayed on the surface to carry out the reaction. After the reaction is completed, the mixture is freeze-dried to obtain the final product. The mass ratio of NIPAAm-sodium lignincarboxylate, hydroxypropyl cellulose, and sodium alginate is 4~9:1~3:2~6.

2. The method for preparing biomass-based air-collecting hydrogel as described in claim 1, characterized in that, Sodium lignin carboxylate was prepared using purified lignin as a raw material. The method for preparing the purified lignin included: The sulfate pulp black liquor was diluted with water and filtered to obtain a preliminarily purified black liquor. It was then stirred and dispersed, and a dilute acid solution was added to precipitate lignin. After washing and purification, purified lignin was obtained.

3. The method for preparing biomass-based air-collecting hydrogel as described in claim 2, characterized in that, The weight-volume concentration of the diluted sulfate pulp black liquor is 5-10%. Alternatively, add a dilute acid solution to adjust the pH of the black liquor to 3-4.

4. The method for preparing biomass-based air-collecting hydrogel as described in claim 2, characterized in that, The method for preparing sodium lignin carboxylate includes: adding alkali to make the purified lignin alkaline, adding chloroacetic acid, and heating to carry out a grafting reaction; after the reaction is completed, cooling and diluting the reaction solution, adjusting the pH value, adding anhydrous ethanol, stirring until the solution is turbid, separating the solid and liquid, and collecting the precipitate; washing the precipitate to obtain sodium lignin carboxylate.

5. The method for preparing biomass-based air-collecting hydrogel as described in claim 4, characterized in that, Add alkali to adjust the pH of the purified lignin to 12-13; Alternatively, the mass ratio of lignin to chloroacetic acid is 1:2 to 1:4; Alternatively, the grafting reaction temperature is 60-70℃, and the reaction time is 4-6 hours; Alternatively, after the grafting reaction is completed, the pH of the reaction solution is adjusted to 3-4; the volume ratio of the reaction solution to anhydrous ethanol is 1:0.5-1:

2.

6. The method for preparing biomass-based air-collecting hydrogel as described in claim 1, characterized in that, The ratio of sodium lignin carboxylate to N-isopropylacrylamide is 1:3-1:5; Alternatively, the initiator may be ammonium persulfate; Alternatively, the amount of the initiator is 0.5-2.5 wt% of the total mass of sodium lignin carboxylate and N-isopropylacrylamide.

7. The method for preparing biomass-based air-collecting hydrogel as described in claim 1, characterized in that, The volume ratio of the reaction solution to anhydrous ethanol is 1:0.5-1:

2.

8. The method for preparing biomass-based air-collecting hydrogel as described in claim 1, characterized in that, The concentration of the calcium salt solution is 3-6 wt%.

9. The biomass-based air-collecting hydrogel prepared by the method according to any one of claims 1-8.

10. The application of the biomass-based air-collecting gel according to claim 9 in the preparation of a water collector.