Preparation method of straw biomass-based water-retaining agent

Abstract

The invention discloses a preparation method of a straw biomass-based water-retaining agent, and belongs to the technical field of water-retaining agent preparation, crushed straw is used as a raw material and is sequentially treated by sodium hydroxide, hydrogen peroxide and dimethylformamide to obtain a three-stage product with multiple grafting reaction sites, the combination of straw powder and sodium carboxymethyl cellulose is promoted, and the straw biomass-based water-retaining agent is prepared. The water-retaining agent with a stable structure is further prepared; in addition, solid salicylic acid powder is added after the third-stage product is subjected to high-temperature and high-pressure treatment, so that the solid salicylic acid powder enters the expanded straw powder, then the solid salicylic acid powder is heated and decomposed through high-temperature treatment, and part of the decomposed product is moved out in the form of gas to form holes; the residual product is combined with subsequently added adipic acid dihydrazide to generate a molecular chain with good stretching and overturning properties, so that the water absorption expansion performance of the prepared water-retaining agent is further improved, salicylic acid is decomposed to form a porous structure, the water storage performance of the water-retaining agent is further improved, and the water-retaining agent prepared by adopting the method is good in comprehensive performance and can be widely applied to the field of water retaining agents. Good application prospects are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of water-retaining agent preparation, and in particular to a method for preparing a straw biomass-based water-retaining agent. Background Art

[0002] With global climate change and shifts in agricultural production practices, water scarcity has become a significant factor impacting sustainable agricultural development. Soil moisture loss severely restricts crop growth and yield. Therefore, developing highly effective water-retaining agents to enhance soil water retention has become a key area of agricultural research.

[0003] Currently, water-retaining agents on the market are primarily divided into three categories: starch-based, cellulose-based, and synthetic. Starch-based water-retaining agents are made from natural starches such as corn starch, potato starch, and cassava starch through chemical grafting or modification. While starch-based water-retaining agents have a wide range of raw material sources and are relatively low cost, they suffer from poor mold resistance and are easily degraded, resulting in a short service life. Synthetic water-retaining agents are primarily synthesized from petrochemical monomers such as acrylates and acrylamide through chemical reactions. While these agents have excellent water absorption and water retention, they also suffer from poor degradation and environmental pollution. Cellulose-based water-retaining agents are made from natural cellulose such as straw and wood pulp through chemical modifications such as etherification and esterification. Compared to starch-based and synthetic water-retaining agents, cellulose-based water-retaining agents exhibit superior mold resistance and biodegradability, offering promising application prospects. Straw, a byproduct of agricultural production, including corn straw and wheat straw, is produced in significant quantities. Using straw as a raw material for cellulose-based water-retaining agents offers advantages such as a wide raw material source and low cost. Furthermore, the recycling of straw resources is more aligned with the concept of sustainable development. However, the straw cellulose molecular chain is a highly ordered crystalline structure formed by hydrogen bonds, which has strong rigidity. Its highly ordered crystalline structure leads to fewer reactive active sites, and its strong rigidity leads to poor water absorption and swelling properties. Therefore, the prepared water-retaining agent has poor water absorption and swelling properties, which limits its application performance in soil water retention.

[0004] Therefore, there is a need to find a method for preparing a cellulose water-retaining agent using straw as raw material to solve the problem that when using straw as a cellulose raw material to prepare a water-retaining agent, the prepared water-retaining agent has poor water absorption and swelling properties due to the structural limitations of the straw itself, thereby limiting its applicability in soil water retention. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for preparing a straw biomass-based water-retaining agent, so as to solve the problem that when using straw as a cellulose raw material to prepare a water-retaining agent, the water-retaining agent prepared has poor water absorption and swelling properties due to the structural limitations of the straw itself, thereby limiting its applicability in soil water retention.

[0006] The present invention solves the above technical problems through the following technical means:

[0007] A method for preparing a straw biomass-based water-retaining agent, the preparation method is specifically as follows:

[0008] (1) washing and drying the straw and then crushing it into straw powder; adding the straw powder into a sodium hydroxide-ethanol mixture, heating it to 60-80° C. and reacting it for 12-24 hours; filtering and washing it after the reaction is complete to obtain a primary product;

[0009] (2) placing the primary product in a 5-10 wt% hydrogen peroxide solution, heating to 60-80°C for reaction for 12-24 hours, and filtering and washing to obtain a secondary product after the reaction is complete;

[0010] (3) placing the secondary product in a 5 wt% dimethylformamide solution, heating to 60-80°C for reaction for 12-24 hours, and filtering and washing to obtain a tertiary product after the reaction is complete;

[0011] (4) The tertiary product is placed in a reactor, water is added and stirred to disperse, and after high temperature and high pressure treatment, solid salicylic acid powder is added after cooling to room temperature, and the mixture is slowly stirred and mixed for 20 to 30 minutes, and then filtered to remove water. After standing overnight, the surface moisture is dried at 45°C, and then heat-treated at 220°C for 60 minutes to obtain the quaternary product;

[0012] (5) adding the quaternary product into water, stirring and dispersing, adding adipic acid dihydrazide, and then adding p-toluenesulfonic acid, heating to 80-90° C., stirring and reacting for 2-3 hours, filtering and removing the filtrate, and washing to obtain pretreated straw powder;

[0013] (6) Prepare a sodium hydroxide-urea mixture, add pretreated straw powder at -5°C to -12°C, stir continuously and add sodium carboxymethyl cellulose, then add epichlorohydrin and stir to react for 10 to 20 minutes. After the reaction is completed, keep it at -5°C to -12°C and let it stand overnight to obtain a water-retaining agent primary product; wash the water-retaining agent primary product in deionized water, dry the surface moisture, and then dry it in a freeze drying box to obtain a water-retaining agent finished product.

[0014] The present invention sequentially treats straw powder with alkali, hydrogen peroxide and an organic solvent through steps (1) to (3) to destroy the original chemical bonds between molecular chains in the straw powder, thereby destroying the ordered structure and crystallinity thereof, exposing more reactive sites to obtain a tertiary product with more reactive sites; thereby ensuring that the subsequent reaction with sodium carboxymethyl cellulose is sufficient to form a water-retaining agent with a stable three-dimensional network structure.

[0015] In order to better improve the water absorption and swelling properties of the water retaining agent, the present invention performs high-temperature and high-pressure treatment on the tertiary product straw powder in step (4) to fully expand it, and then adds solid salicylic acid powder after cooling to room temperature. The solid salicylic acid powder adheres to the surface of the expanded straw powder and penetrates into the expanded straw powder. Then, the mixture is heat-treated at 220° C. At this temperature, the solid salicylic acid powder decomposes at high temperature to produce phenol and carbon dioxide, wherein the phenolic hydroxyl group increases the water absorption site of the expanded straw powder, and the carbon dioxide escapes in the form of gas to form a pore structure, thereby increasing the water molecule adsorption site and pore structure of the water retaining agent prepared subsequently, thereby improving the water absorption of the water retaining agent;

[0016] The present invention then adds adipic acid dihydrazide to react in step (5), whereby the adipic acid dihydrazide covalently bonds to the phenolic hydroxyl site formed in step (4). The carbon chain structure in the adipic acid dihydrazide has good flipping and stretching properties, thereby allowing the water-retaining agent to swell highly after absorbing water and ensuring that the molecular chains are well connected and not broken, firmly retaining moisture after sufficient water absorption. Pretreated straw powder is obtained through the treatment of steps (1) to (5) of the present invention, and then sodium carboxymethyl cellulose is added to polymerize with the pretreated straw powder to form a stable three-dimensional network structure, thereby preparing a water-retaining agent with good water absorption and swelling properties.

[0017] Furthermore, the sodium hydroxide-ethanol mixed solution in step (1) is obtained by mixing 5-10 wt% sodium hydroxide solution and 5-10 wt% ethanol solution, and the mass ratio of the sodium hydroxide solution to the ethanol solution is 1:1.

[0018] Furthermore, the high temperature and high pressure treatment in step (4) is specifically performed at 180-250° C. and a pressure of 3-5 MPa for 20-40 minutes.

[0019] Furthermore, in the step (4), the mass ratio of the tertiary product to the solid salicylic acid powder is (8-10): (2-3).

[0020] Furthermore, in the step (5), the mass ratio of the quaternary product to adipic acid dihydrazide and p-toluenesulfonic acid is (8-10): (0.8-1): (0.1-0.2).

[0021] Furthermore, in the sodium hydroxide-urea mixed solution in step (6), the mass ratio of sodium hydroxide, urea and water is 7:12:81.

[0022] Furthermore, in step (6), the mass ratio of the sodium hydroxide-urea mixed solution, the pretreated straw powder, sodium carboxymethyl cellulose, and epichlorohydrin is (200-250): (8-10): (8-10): (8.64-10.8).

[0023] Furthermore, the surface moisture drying temperature in step (6) is 50-60°C.

[0024] Furthermore, the freeze-drying temperature in step (6) is -50°C to -80°C.

[0025] Beneficial effects:

[0026] 1. The present invention uses waste straw as raw material to prepare the water-retaining agent, which reduces the problem of waste disposal and promotes the recycling of resources. In addition, the water-retaining agent prepared using straw as raw material has good biodegradability.

[0027] 2. The straw powder is treated by the method of the present invention to obtain pretreated straw powder with more grafting sites, and then a mild and easy-to-control grafting reaction is carried out with sodium carboxymethyl cellulose to prepare a water-retaining agent with good comprehensive performance, which can effectively improve the water retention capacity of the soil and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 : This is a picture of the untreated straw raw material in Example 1 of the present invention;

[0029] Figure 2 : This is a picture of the initial product of the water-retaining agent in Example 1 of the present invention;

[0030] Figure 3 : This is a picture of the cost of the water-retaining agent product of Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below with reference to specific embodiments and accompanying drawings:

[0032] Example 1: Preparation of water-retaining agent

[0033] (1) After washing the straw, drying the surface moisture at 60°C, and then crushing it into straw powder with a particle size of 0.1 to 0.5 cm; mixing 6wt% sodium hydroxide solution and 6wt% ethanol solution in a mass ratio of 1:1 to obtain a sodium hydroxide-ethanol mixture; then adding the straw powder to the sodium hydroxide-ethanol mixture in a mass ratio of 1:5, stirring and mixing evenly, heating to 70°C and reacting for 18 hours; after the reaction is completed, filtering and removing the filtrate, and washing with clean water twice to obtain a primary product;

[0034] (2) The primary product was placed in a 7 wt% hydrogen peroxide solution at a solid-liquid mass ratio of 1:5, heated to 70°C and reacted for 18 h. After the reaction was complete, the filtrate was filtered out and washed twice with clean water to obtain a secondary product;

[0035] (3) The secondary product was placed in a 5 wt% dimethylformamide solution at a solid-liquid mass ratio of 1:5, heated to 70°C and reacted for 18 h. After the reaction was complete, the filtrate was filtered out and washed twice with clean water to obtain a tertiary product;

[0036] (4) 9 g of the tertiary product was placed in a reactor, 450 g of water was added and stirred, and the mixture was treated at 200°C and 4 MPa for 30 min. The mixture was then cooled to room temperature at a rate of 10°C / min and 2.5 g of solid salicylic acid powder was added. The mixture was slowly stirred and mixed for 25 min, and then filtered to remove water. The mixture was allowed to stand overnight, dried at 45°C, and then kept at 220°C for 60 min to obtain a quaternary product.

[0037] (5) 9 g of the fourth-stage product was added to 450 g of water, stirred and dispersed, and then 0.9 g of adipic acid dihydrazide was added, followed by 0.15 g of p-toluenesulfonic acid. The mixture was heated to 85 ° C. and stirred for 2.5 h. After that, the filtrate was filtered out and washed twice with clean water to obtain pretreated straw powder;

[0038] (6) A sodium hydroxide-urea mixture was prepared according to a mass ratio of sodium hydroxide: urea: water = 7:12:81; 225 g of the sodium hydroxide-urea mixture was taken, 9 g of pretreated straw powder was added at -10°C, and 9 g of sodium carboxymethyl cellulose was slowly added while stirring continuously, and then 9.72 g of epichlorohydrin was added and stirred for 15 minutes. After the reaction was completed, the mixture was kept at -10°C and allowed to stand overnight to obtain a water-retaining agent primary product; the water-retaining agent primary product was washed in deionized water, dried at 55°C to remove surface moisture, and then placed in a freeze drying oven and dried at -50°C to obtain a water-retaining agent finished product.

[0039] Example 2: Preparation of water-retaining agent 2

[0040] (1) After washing the straw, drying the surface moisture at 60°C, and then crushing it into straw powder with a particle size of 0.1 to 0.5 cm; mixing 5wt% sodium hydroxide solution and 5wt% ethanol solution in a mass ratio of 1:1 to obtain a sodium hydroxide-ethanol mixture; then adding the straw powder to the sodium hydroxide-ethanol mixture in a mass ratio of 1:5, stirring and mixing evenly, heating to 60°C and reacting for 24 hours; after the reaction is completed, filtering and removing the filtrate, and washing with clean water twice to obtain a primary product;

[0041] (2) The primary product was placed in a 5 wt% hydrogen peroxide solution at a solid-liquid mass ratio of 1:5, heated to 60°C and reacted for 24 h. After the reaction was complete, the filtrate was filtered out and washed twice with clean water to obtain a secondary product;

[0042] (3) The secondary product was placed in a 5 wt% dimethylformamide solution at a solid-liquid mass ratio of 1:5, heated to 60°C and reacted for 24 h. After the reaction was complete, the filtrate was filtered out and washed twice with clean water to obtain a tertiary product;

[0043] (4) 8 g of the tertiary product was placed in a reactor, 400 g of water was added and stirred and dispersed, and the mixture was treated at 180°C and 3 MPa for 40 min. The mixture was then cooled to room temperature at a rate of 10°C / min and 2 g of solid salicylic acid powder was added. The mixture was slowly stirred and mixed for 20 min, and then filtered to remove water. The mixture was allowed to stand overnight, dried at 45°C, and then kept at 220°C for 60 min to obtain a quaternary product.

[0044] (5) 8 g of the fourth-grade product was added to 400 g of water, stirred and dispersed, and then 0.8 g of adipic acid dihydrazide was added, followed by 0.1 g of p-toluenesulfonic acid. The mixture was heated to 80 ° C. and stirred for 2 h. After that, the filtrate was filtered out and washed twice with clean water to obtain pretreated straw powder;

[0045] (6) A sodium hydroxide-urea mixture was prepared according to a mass ratio of sodium hydroxide: urea: water = 7:12:81; 200 g of the sodium hydroxide-urea mixture was added to 8 g of pretreated straw powder at -5°C, and the mixture was stirred continuously and slowly added with 8 g of sodium carboxymethyl cellulose, and then 8.64 g of epichlorohydrin was added and stirred for 10 minutes. After the reaction was completed, the mixture was kept at -5°C and allowed to stand overnight to obtain a water-retaining agent primary product; the water-retaining agent primary product was washed in deionized water, dried at 50°C to remove surface moisture, and then placed in a freeze drying oven and dried at -50°C to obtain a water-retaining agent finished product.

[0046] Example 3: Preparation of water-retaining agent

[0047] (1) After washing the straw, drying the surface moisture at 60°C, and then grinding it into straw powder with a particle size of 0.1 to 0.5 cm; mixing 10 wt% sodium hydroxide solution and 10 wt% ethanol solution in a mass ratio of 1:1 to obtain a sodium hydroxide-ethanol mixture; then adding the straw powder to the sodium hydroxide-ethanol mixture in a mass ratio of 1:5, stirring and mixing evenly, heating to 80°C and reacting for 12 hours; after the reaction is completed, filtering and removing the filtrate, and washing with clean water twice to obtain a primary product;

[0048] (2) The primary product was placed in a 10 wt% hydrogen peroxide solution at a solid-liquid mass ratio of 1:5, heated to 80°C and reacted for 12 h. After the reaction was complete, the filtrate was filtered out and washed twice with clean water to obtain a secondary product;

[0049] (3) The secondary product was placed in a 5 wt% dimethylformamide solution at a solid-liquid mass ratio of 1:5, heated to 80°C and reacted for 12 h. After the reaction was complete, the filtrate was filtered out and washed twice with clean water to obtain a tertiary product;

[0050] (4) 10 g of the tertiary product was placed in a reactor, 500 g of water was added and stirred and dispersed, and the mixture was treated at 250°C and 5 MPa for 20 min. The mixture was then cooled to room temperature at a rate of 10°C / min and 3 g of solid salicylic acid powder was added. The mixture was slowly stirred and mixed for 30 min, and then filtered to remove water. The mixture was allowed to stand overnight and dried at 45°C to dry the surface moisture. The mixture was then kept at 220°C for 60 min to obtain a quaternary product.

[0051] (5) Take 10g of the fourth-grade product and add it to 500g of water, stir and disperse it, then add 1g of adipic acid dihydrazide, and then add 2g of p-toluenesulfonic acid. Heat it to 90°C and stir to react for 2h. After that, filter and remove the filtrate, and wash it with clean water twice to obtain pretreated straw powder;

[0052] (6) A sodium hydroxide-urea mixture was prepared according to a mass ratio of sodium hydroxide: urea: water = 7:12:81; 250 g of the sodium hydroxide-urea mixture was taken, 10 g of pretreated straw powder was added at -12°C, 10 g of sodium carboxymethyl cellulose was slowly added while stirring continuously, and then 10.8 g of epichlorohydrin was added and stirred for 20 minutes. After the reaction was completed, the mixture was kept at -12°C and allowed to stand overnight to obtain a water-retaining agent primary product; the water-retaining agent primary product was washed in deionized water, dried at 60°C to remove surface moisture, and then placed in a freeze drying oven and dried at -50°C to obtain a water-retaining agent finished product.

[0053] Comparative Example 1: Preparation of water-retaining agent

[0054] In contrast to Example 1, the only difference is that in the preparation of the water-retaining agent in Comparative Example 1, the straw powder is not treated with a sodium hydroxide-ethanol mixture in step (1), but is directly treated in water, as shown below:

[0055] (1) After washing the straw, drying the surface moisture at 60°C, and then crushing it into straw powder with a particle size of 0.1 to 0.5 cm; then adding the straw powder to water at a mass ratio of 1:5, stirring and mixing, heating to 70°C and reacting for 18 hours. After the reaction is completed, the filtrate is filtered to remove the filtrate, and washing with clean water twice to obtain the primary product;

[0056] (2) to (6) are the same as in Example 1.

[0057] Comparative Example 2: Preparation of water-retaining agent

[0058] In contrast to Example 1, the only difference is that in the preparation of the water-retaining agent in Comparative Example 2, the primary product straw is not treated with hydrogen peroxide solution in step (2), but is directly treated in water, as shown below:

[0059] (1) Same as Example 1;

[0060] (2) The primary product was placed in water at a solid-liquid mass ratio of 1:5, heated to 70°C and reacted for 18 hours. After the reaction was complete, the filtrate was filtered out and washed twice with clean water to obtain the secondary product;

[0061] (3) to (6) are the same as in Example 1.

[0062] Comparative Example 3: Preparation of water-retaining agent

[0063] In contrast to Example 1, the only difference is that in the preparation of the water-retaining agent in Comparative Example 3, the dimethylformamide solution is not used for treatment in step (3), but the treatment is carried out directly in water, as shown below:

[0064] (1) to (2) are the same as in Example 1;

[0065] (3) The secondary product was placed in water at a solid-liquid mass ratio of 1:5, heated to 70°C and reacted for 18 hours. After the reaction was complete, the filtrate was filtered out and washed twice with clean water to obtain the tertiary product;

[0066] (4) to (6) are the same as in Example 1.

[0067] Comparative Example 4: Preparation of water-retaining agent

[0068] In contrast to Example 1, the only difference is that the high temperature and high pressure treatment is not performed in step (4) when preparing the water-retaining agent in Comparative Example 4, as shown below:

[0069] (1) to (3) are the same as in Example 1;

[0070] (4) 9 g of the third-stage product was placed in a reactor, 450 g of water was added and stirred to disperse, and then 2.5 g of solid salicylic acid powder was added. The mixture was slowly stirred and mixed for 25 min, and then filtered to remove water. After standing overnight, the surface moisture was dried at 45°C and then kept at 220°C for 60 min to obtain the fourth-stage product.

[0071] (5) to (6) are the same as in Example 1.

[0072] Comparative Example 5: Preparation of water-retaining agent

[0073] In contrast to Example 1, the only difference is that solid salicylic acid powder is not added in step (4) when preparing the water-retaining agent in Comparative Example 5, as shown below:

[0074] (1) to (3) are the same as in Example 1;

[0075] (4) 9 g of the tertiary product was placed in a reactor, 450 g of water was added, and the mixture was stirred and dispersed. The mixture was treated at 200°C and 4 MPa for 30 min, and then filtered to remove water. The mixture was allowed to stand overnight and dried at 45°C to dry the surface moisture. The mixture was then kept at 220°C for 60 min to obtain the quaternary product.

[0076] (5) to (6) are the same as in Example 1.

[0077] Comparative Example 6: Preparation of water-retaining agent

[0078] In contrast to Example 1, the only difference is that in the preparation of the water-retaining agent in Comparative Example 6, after drying the surface moisture in step (4), no heat preservation treatment is performed, as shown below:

[0079] (1) to (3) are the same as in Example 1;

[0080] (4) 9 g of the third-stage product was placed in a reactor, 450 g of water was added and stirred, and the mixture was treated at 200°C and 4 MPa for 30 min. The mixture was then cooled to room temperature at a rate of 10°C / min and 2.5 g of solid salicylic acid powder was added. The mixture was slowly stirred and mixed for 25 min, and then filtered to remove water. The mixture was allowed to stand overnight and dried at 45°C to obtain the fourth-stage product.

[0081] (5) to (6) are the same as in Example 1.

[0082] Comparative Example 7: Preparation of water-retaining agent

[0083] In contrast to Example 1, the only difference is that the water-retaining agent in Comparative Example 7 lacks step (5) in the preparation of the water-retaining agent. The pretreated straw powder (quaternary product) obtained by directly treating with steps (1) to (4) is reacted and grafted with sodium carboxymethyl cellulose to obtain the water-retaining agent, as shown below:

[0084] (1) to (4) are the same as in Example 1;

[0085] (5) A sodium hydroxide-urea mixture was prepared according to a mass ratio of sodium hydroxide: urea: water = 7:12:81; 225 g of the sodium hydroxide-urea mixture was added to 9 g of pretreated straw powder (fourth-level product) at -10°C, and the mixture was stirred continuously and slowly added with 9 g of sodium carboxymethyl cellulose, and then 9.72 g of epichlorohydrin was added and stirred for 15 minutes. After the reaction was completed, the mixture was kept at -10°C and allowed to stand overnight to obtain a water-retaining agent primary product; the water-retaining agent primary product was washed in deionized water, dried at 55°C to remove surface moisture, and then placed in a freeze drying oven and dried at -50°C to obtain a water-retaining agent finished product.

[0086] Comparative Example 8: Preparation of water-retaining agent

[0087] In contrast to Example 1, the only difference is that in the preparation of the water-retaining agent in Comparative Example 8, steps (4) and (5) are omitted, and the pretreated straw powder (tertiary product) obtained by directly processing through steps (1) to (3) is reacted with sodium carboxymethyl cellulose, as shown below:

[0088] (1) to (3) are the same as in Example 1

[0089] (4) A sodium hydroxide-urea mixture was prepared according to a mass ratio of sodium hydroxide: urea: water = 7:12:81; 225 g of the sodium hydroxide-urea mixture was added to 9 g of pretreated straw powder (tertiary product) at -10°C, and the mixture was stirred continuously and slowly added with 9 g of sodium carboxymethyl cellulose, and then 9.72 g of epichlorohydrin was added and stirred for 15 minutes. After the reaction was completed, the mixture was kept at -10°C and allowed to stand overnight to obtain a water-retaining agent primary product; the water-retaining agent primary product was washed in deionized water, dried at 55°C to remove surface moisture, and then placed in a freeze drying oven and dried at -50°C to obtain a water-retaining agent finished product.

[0090] Experiment: Water-retaining agent performance test

[0091] The properties of the water-retaining agents prepared in Example 1 and Comparative Examples 1 to 8 were tested, specifically including water absorption capacity, repeated swelling capacity, and water retention capacity. The testing methods are as follows:

[0092] (1) Water absorption test method:

[0093] Weigh 1g of dry water-retaining agent sample and place it in deionized water. Drain the water on the surface of the water-retaining agent every 30 minutes, weigh and record the weight of the water-retaining agent, until the water-retaining agent is fully swollen (weight no longer changes), that is, the maximum water absorption capacity of the water-retaining agent is reached. Weigh the water-retaining agent after water absorption and calculate the water absorption rate of the water-retaining agent: water absorption rate = (weight of water-retaining agent after water absorption - weight of water-retaining agent before water absorption) / weight of water-retaining agent before water absorption;

[0094] (2) Repeated swelling ability test method:

[0095] Weigh 1g of water-retaining agent sample into a beaker, add distilled water, and place it at room temperature for 5 hours to allow the water-retaining agent to completely swell. Then place the completely swollen water-retaining agent in a constant temperature blast drying oven at 60℃ until the sample is completely dry. Then add an equal volume of distilled water to swell it again. Repeat the above process 5 times and calculate the water absorption rate of the water-retaining agent after the fifth swelling.

[0096] (3) Water retention capacity test method:

[0097] Prepare soil samples with an initial moisture content of 70%, mix the soil sample and water retaining agent at a mass ratio of soil: water retaining agent = 10:1, place them at 30℃ to simulate drought stress, and then test the soil moisture content again after 20h and 60h; add a blank control group when testing the water retention capacity (specifically, the soil sample without water retaining agent added is the blank control group).

[0098] The performance of the water-retaining agents of Example 1 and Comparative Examples 1 to 8 was tested by repeating the experiment three times according to the above method, and the average data were shown in Table 1.

[0099] Table 1

[0100] Water absorption Water absorption after 5 swelling times 20h water content (%) 60h water content (%) Example 1 253 206 59.6 26.4 Comparative Example 1 228 172 53.6 18.7 Comparative Example 2 236 174 54.3 19.0 Comparative Example 3 239 180 55.0 19.6 Comparative Example 4 235 168 52.5 17.1 Comparative Example 5 221 155 50.7 14.3 Comparative Example 6 209 148 49.2 13.5 Comparative Example 7 220 140 53.3 17.8 Comparative Example 8 197 109 47.1 11.2 Blank control —— —— 20.3 0.0

[0101] According to the data analysis in Table 1, we can see that:

[0102] (1) The water-retaining agent prepared by the present invention can absorb water up to 253 times, and the water absorption rate reaches 206 times after repeated swelling for 5 times, indicating that the water-retaining agent prepared by the present invention has good water absorption and good swelling performance. The water absorption rate can still reach 206 times after repeated swelling for 5 times; when used for water conservation in soil, it can well absorb and retain moisture in the soil. Under drought stress at 30°C, the soil moisture content is 59.6% after 20 hours and 26.4% after 60 hours, which shows that the water-retaining agent has good application prospects in soil water conservation.

[0103] (2) In comparative example 1, the straw powder was not treated with a sodium hydroxide-ethanol mixture during the preparation of the water-retaining agent. The degree of destruction of the crystalline structure of the straw cellulose was low, resulting in less exposure of active sites such as hydroxyl groups, thereby affecting the subsequent reaction and bonding, and the prepared water-retaining agent had poor performance. In comparative example 2, the primary product straw was not treated with a hydrogen peroxide solution during the preparation of the water-retaining agent. In comparative example 3, the dimethylformamide solution was not used during the preparation of the water-retaining agent. The purity of the straw powder cellulose in comparative examples 2 to 3 was low, the active reaction sites were reduced, and the subsequent reaction was affected, thereby reducing the performance of the water-retaining agent.

[0104] (3) In comparative example 4, the water-retaining agent was not subjected to high-temperature and high-pressure treatment during preparation, and the straw powder failed to fully swell, resulting in obstruction of the solid salicylic acid powder from entering the interior, failure to form a better pore structure and affecting subsequent reactions. The performance of the prepared water-retaining agent was poor. In comparative example 5, solid salicylic acid powder was not added during preparation of the water-retaining agent, and the performance of the water-retaining agent was significantly reduced. In comparative example 6, the water-retaining agent was not subjected to high-temperature insulation treatment after drying the surface moisture during preparation, and the solid salicylic acid powder inside failed to undergo thermal decomposition, which instead reduced the water absorption performance of the water-retaining agent. In comparative example 7, adipic acid dihydrazide was not added during preparation of the water-retaining agent, and the prepared water-retaining agent had poor repeated swelling performance, and the water absorption rate was significantly reduced after swelling 5 times.

[0105] The above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art will appreciate that the technical solutions of the present invention may be modified or replaced with equivalents without departing from the spirit and scope of the technical solutions of the present invention, and such modifications or equivalents shall be encompassed by the claims of the present invention. Any techniques, shapes, and structures not described in detail herein are well known.

Claims

1. A method for preparing a straw biomass-based water-retaining agent, characterized in that: The preparation method is as follows: (1) washing and drying the straw and then crushing it into straw powder; adding the straw powder into a sodium hydroxide-ethanol mixture, heating it to 60-80° C. and reacting it for 12-24 hours; filtering and washing it after the reaction is complete to obtain a primary product; (2) placing the primary product in a 5-10 wt% hydrogen peroxide solution, heating to 60-80°C for reaction for 12-24 hours, and filtering and washing to obtain a secondary product after the reaction is complete; (3) placing the secondary product in a 5 wt% dimethylformamide solution, heating to 60-80°C for 12-24 hours, and filtering and washing to obtain a tertiary product after the reaction is complete; (4) The tertiary product is placed in a reactor, water is added and stirred to disperse, and after high temperature and high pressure treatment, it is cooled to room temperature and solid salicylic acid powder is added, stirred and mixed for 20 to 30 minutes, and then filtered to remove water. After standing overnight, the surface moisture is dried at 45°C, and then heat-treated at 220°C for 60 minutes to obtain the quaternary product; (5) adding the quaternary product into water, stirring and dispersing, adding adipic acid dihydrazide, and then adding p-toluenesulfonic acid, heating to 80-90° C., stirring and reacting for 2-3 hours, filtering and removing the filtrate, and washing to obtain pretreated straw powder; (6) Prepare a sodium hydroxide-urea mixture, add pretreated straw powder at -5°C to -12°C, stir continuously and add sodium carboxymethyl cellulose, then add epichlorohydrin and stir to react for 10 to 20 minutes. After the reaction is completed, keep it at -5°C to -12°C and let it stand overnight to obtain a water-retaining agent primary product; wash the water-retaining agent primary product in deionized water, dry the surface moisture, and then dry it in a freeze drying box to obtain a water-retaining agent finished product.

2. The method for preparing a straw biomass-based water-retaining agent according to claim 1, wherein: The sodium hydroxide-ethanol mixed solution in step (1) is obtained by mixing 5-10 wt% sodium hydroxide solution and 5-10 wt% ethanol solution, and the mass ratio of the sodium hydroxide solution to the ethanol solution is 1:

1.

3. The method for preparing a straw biomass-based water-retaining agent according to claim 2, wherein: The high temperature and high pressure treatment in step (4) is specifically performed at 180-250° C. and a pressure of 3-5 MPa for 20-40 minutes.

4. The method for preparing a straw biomass-based water-retaining agent according to claim 3, wherein: The mass ratio of the tertiary product to the solid salicylic acid powder in the step (4) is (8-10): (2-3).

5. The method for preparing a straw biomass-based water-retaining agent according to claim 4, characterized in that: In the step (5), the mass ratio of the quaternary product to adipic acid dihydrazide and p-toluenesulfonic acid is (8-10): (0.8-1): (0.1-0.2).

6. The method for preparing a straw biomass-based water-retaining agent according to claim 5, characterized in that: In the step (6), the mass ratio of sodium hydroxide, urea and water in the sodium hydroxide-urea mixed solution is 7:12:

81.

7. The method for preparing a straw biomass-based water-retaining agent according to claim 6, characterized in that: In the step (6), the mass ratio of the sodium hydroxide-urea mixed solution, the pretreated straw powder, sodium carboxymethyl cellulose and epichlorohydrin is (200-250): (8-10): (8-10): (8.64-10.8).

8. The method for preparing a straw biomass-based water-retaining agent according to claim 7, characterized in that: The surface moisture drying temperature in step (6) is 50-60°C.

9. The method for preparing a straw biomass water retaining agent according to claim 8, characterized in that: The freeze-drying temperature in step (6) is -50°C to -80°C.

Images