Green preparation process of soybean straw-based multifunctional degradable water-retaining agent

Abstract

The application discloses a green preparation process of a soybean straw-based multifunctional degradable water-retaining agent, and belongs to the technical field of agricultural and forestry waste resource utilization and water-retaining agent preparation. The application takes waste soybean straw as a core renewable raw material, and the multifunctional degradable water-retaining agent is prepared through the following procedures: pretreatment, green activation modification by using low-concentration dilute alkali, acrylic acid-acrylamide graft polymerization, green crosslinking, functional compounding of humic acid potassium and bentonite, drying, crushing and forming. The preparation process is green and pollution-free, the reaction condition is mild, the energy consumption is low, and the process is simple, so that efficient resource utilization of soybean straw waste can be realized, and the technical pain points, such as pollution and waste in traditional straw treatment, difficulty in degradation of chemical water-retaining agents, secondary soil pollution caused by the chemical water-retaining agents, and single function, are solved.

Description

Technical Field

[0001] This invention belongs to the field of agricultural and forestry waste resource utilization and polymer water-retaining agent preparation technology, specifically involving a green preparation process of a soybean straw-based multifunctional biodegradable water-retaining agent. Background Technology

[0002] Soybeans are a major grain and oil crop in my country, with a vast annual planting area, resulting in a massive amount of soybean straw waste. Traditional disposal methods mainly involve on-site burning, indiscriminate dumping, or simple landfilling, which not only causes serious waste of agricultural and forestry biomass resources but also leads to air pollution, soil compaction, and other environmental problems, which are inconsistent with the development concepts of green agriculture and circular economy.

[0003] Water-retaining agents are a class of highly absorbent polymer materials widely used in agricultural drought resistance, landscaping, soil improvement, and ecological restoration. Currently, most mainstream water-retaining agents on the market are chemically synthesized polyacrylate products, which have drawbacks such as poor biodegradability, easy secondary pollution caused by residues in the soil, non-renewable raw materials, and high production costs. Long-term use can damage the soil microbial environment, affect crop growth, and restrict the sustainable development of ecological agriculture.

[0004] Existing technologies for preparing agricultural and forestry straw-based water-retaining agents often suffer from problems such as complex processes, low modification efficiency, poor water absorption and retention performance, limited functionality, the need for large amounts of chemical reagents in the preparation process, and potential pollution risks. Most processes only achieve a single water absorption function, lacking multi-functional properties such as soil improvement, fertilizer retention, and slow release. Furthermore, the utilization rate of straw resources is low, and the finished product exhibits poor salt tolerance and repeated water absorption performance, failing to meet the demands of modern agriculture for refined, green, and multi-functional applications. Therefore, developing a simple, green, and pollution-free process for preparing soybean straw-based water-retaining agents that achieves high straw utilization, and whose finished product possesses multiple multi-functional properties including high water absorption and retention, complete biodegradability, and fertilizer retention and soil improvement, has significant practical importance and application value. Summary of the Invention

[0005] Purpose of the invention

[0006] This invention aims to overcome the shortcomings of existing technologies and provide a green preparation process for a soybean straw-based multifunctional biodegradable water-retaining agent. Using waste soybean straw as the core raw material, the multifunctional water-retaining agent is prepared through green modification, graft polymerization, and cross-linking curing processes, realizing the efficient resource utilization of agricultural and forestry waste. At the same time, it solves the technical problems of traditional chemical water-retaining agents, such as being difficult to degrade, easy to pollute, having single functions, and low cost-effectiveness. The prepared water-retaining agent has multiple properties, including ultra-high water absorption and retention, salt and alkali resistance, biodegradability, slow-release fertilizer retention, and soil improvement. The entire preparation process is green and pollution-free, simple, and low-cost.

[0007] Technical solution

[0008] To achieve the above objectives, the present invention employs the following green preparation process, the specific steps of which are as follows:

[0009] 1. Raw material pretreatment: Select dry soybean straw that is free from mold and rot, remove surface impurities and mud, crush and pass through a 40-80 mesh sieve to obtain straw powder; place the straw powder in a constant temperature drying oven and dry at 60-70℃ for 4-6 hours to remove free moisture, and cool to room temperature for later use.

[0010] 2. Green Alkali Modification: Pretreated straw powder is mixed with deionized water at a solid-liquid ratio of 1:8-1:12 (g / mL) and stirred until a suspension is formed. A low-concentration sodium hydroxide solution is slowly added to the suspension to adjust the pH to 10-11. The mixture is stirred at room temperature for 1.5-2.5 hours to activate and modify the straw cellulose and hemicellulose. After the reaction, the mixture is filtered, and the filter residue is washed with deionized water until neutral. The residue is then dried at 60℃ to obtain modified soybean straw powder. This step uses a low-concentration alkali solution for gentle modification, without high-temperature or high-pressure reactions, and without the addition of any toxic reagents, making it green and environmentally friendly.

[0011] 3. Graft polymerization reaction: Add modified soybean straw powder to a reaction vessel, add an appropriate amount of deionized water and stir to disperse, then heat in a water bath to 50-60℃; slowly add acrylic acid monomer and acrylamide monomer in sequence, the total mass of monomers being 2-4 times the mass of modified straw powder, and the mass ratio of acrylic acid to acrylamide being 2:1; after stirring evenly, add a composite initiator, which is a compound system of potassium persulfate and sodium bisulfite, and the addition amount is 0.3%-0.8% of the total mass of monomers; stir at a constant temperature for 2-3 hours to achieve efficient graft polymerization of monomers and straw cellulose molecules.

[0012] 4. Crosslinking Modification and Functional Compounding: After the grafting reaction is completed, the temperature is raised to 65-75℃, and a small amount of green crosslinking agent N,N'-methylenebisacrylamide is added. The amount added is 0.05%-0.15% of the total mass of the monomers, and the crosslinking reaction is carried out for 30-45 minutes. Then, potassium humate and bentonite ultrafine powder are added for functional compounding. The amount of potassium humate added is 8%-15% of the mass of the modified straw, and the amount of bentonite added is 5%-10%. The mixture is stirred evenly and kept at the temperature for 20 minutes to give the finished product the functions of fertilizer retention, soil improvement and salt and alkali resistance.

[0013] 5. Post-processing and molding: Cool the reaction mixture to room temperature, discharge it and place it in an oven, dry it at a constant temperature of 70-80℃ to constant weight, then crush it and pass it through a 60-mesh sieve to obtain the finished product of powdered soybean straw-based multifunctional biodegradable water-retaining agent.

[0014] Preferably, the sodium hydroxide solution in step 2 has a mass concentration of 2%-4%, which gently activates the straw biomass components, avoids excessive damage to the straw fiber structure, and reduces reagent residue while ensuring the modification effect.

[0015] Preferably, in step 3, the water bath heating rate is controlled at 2℃ / min, and the stirring speed is 300-400r / min to ensure uniform material dispersion and improve graft polymerization efficiency.

[0016] Preferably, the mass ratio of potassium persulfate to sodium bisulfite in the composite initiator is 3:1, which results in high initiation efficiency, few side reactions, and can significantly improve the water absorption ratio of the water-retaining agent.

[0017] Beneficial effects

[0018] Compared with the prior art, the present invention has the following significant advantages:

[0019] 1. Green and renewable raw materials with high resource utilization rate: This invention uses agricultural waste soybean straw as the core raw material, turning waste into treasure, effectively solving the straw pollution problem, reducing the production cost of water-retaining agents, realizing the recycling of agricultural and forestry waste, and meeting the needs of green agriculture and circular economy development.

[0020] 2. The preparation process is green and environmentally friendly: the whole process adopts mild reaction conditions, without high temperature and high pressure, without the addition of toxic and harmful reagents, the alkalization modification uses low concentration dilute alkali, the subsequent water washing has no residual pollution, the reaction by-products are harmless, the process is simple, energy consumption is low, and operation is convenient, making it suitable for large-scale industrial production.

[0021] 3. Excellent product performance and multiple functions: The water-retaining agent prepared by this invention has a water absorption ratio of 300-500 times, and a water absorption ratio of physiological saline of ≥80 times. It has excellent salt and alkali resistance and stable repeated water absorption performance. At the same time, it has multiple functions such as biodegradability, slow release of fertilizer, loosening of soil, and improvement of soil aggregate structure. Potassium humate can supplement soil organic matter, and bentonite can improve soil moisture retention capacity, solving the problems of single function and poor applicability of traditional water-retaining agents in saline-alkali land.

[0022] 4. Completely biodegradable with no secondary pollution: The finished product uses natural straw cellulose as the skeleton and is combined with green modified components. It can be naturally degraded in the soil. The degradation products are organic matter and inorganic salts, which can be directly absorbed and utilized by crops. It completely solves the problem of soil residual pollution caused by traditional chemical water-retaining agents and is suitable for green applications in multiple scenarios such as ecological farmland, landscaping, and desert restoration.

[0023] 5. High cost performance and wide applicability: Compared with commercially available chemical water-retaining agents, the raw material cost of this invention is low, the preparation process is simplified, and the overall production cost is reduced by more than 30%. It can be widely used in many fields such as drought resistance and water retention in farmland, seedling cultivation, slope greening, desert ecological restoration, and potted plant maintenance, and has extremely high market promotion value. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. The following embodiments are only used to explain the present invention and are not intended to limit the scope of protection of the present invention.

[0025] Example 1

[0026] A green preparation process for a soybean straw-based multifunctional biodegradable water-retaining agent includes the following steps:

[0027] 1. Raw material pretreatment: Select dry, mold-free soybean straw, remove impurities, crush it, pass it through a 60-mesh sieve, dry it in a 65℃ drying oven for 5 hours, and then cool it for later use.

[0028] 2. Green alkalization modification: Mix straw powder with deionized water at a solid-liquid ratio of 1:10 (g / mL), add 3% sodium hydroxide solution to adjust the pH to 10.5, stir at room temperature for 2 hours, filter, wash with water until neutral, and dry at 60℃ to obtain modified straw powder.

[0029] 3. Graft polymerization reaction: Take 10g of modified straw powder, add 100mL of deionized water and stir to disperse, heat the water bath to 55℃; add 20g of acrylic acid and 10g of acrylamide, stir evenly and then add 0.15g of composite initiator (0.1125g of potassium persulfate + 0.0375g of sodium bisulfite), and stir at a constant temperature for 2.5h.

[0030] 4. Crosslinking modification and functional compounding: Heat to 70℃, add 0.03g N,N'-methylenebisacrylamide, and crosslink reaction for 40min; then add 1.2g potassium humate and 0.8g bentonite, keep warm and stir for 20min to complete functional compounding.

[0031] 5. Post-processing and molding: Cool to room temperature, dry at 75℃ to constant weight, pulverize and pass through a 60-mesh sieve to obtain the multifunctional biodegradable water-retaining agent product.

[0032] In this embodiment, the finished product has a water absorption rate of 420 times for pure water and 92 times for physiological saline. It can be completely biodegraded in soil within 180 days and has good water retention, fertilizer retention and soil improvement properties.

[0033] Example 2

[0034] A green preparation process for a soybean straw-based multifunctional biodegradable water-retaining agent includes the following steps:

[0035] 1. Raw material pretreatment: Select dry, mold-free soybean straw, crush it through a 40-mesh sieve, dry it at 60℃ for 6 hours, and cool it for later use.

[0036] 2. Green alkalization modification: solid-liquid ratio 1:8 (g / mL), add 2% sodium hydroxide solution to adjust pH to 10, react at room temperature for 2.5h, wash with water to neutralize, and then dry.

[0037] 3. Graft polymerization reaction: 10g of modified straw powder was added to 80mL of deionized water and placed in a 50℃ water bath; 15g of acrylic acid and 7.5g of acrylamide were added, along with 0.07g of composite initiator, and the reaction was carried out for 3 hours.

[0038] 4. Crosslinking modification and functional compounding: Add 0.018g of crosslinking agent at 65℃ and crosslink for 30min; add 0.8g of potassium humate and 0.5g of bentonite for compounding modification.

[0039] 5. Post-processing and molding: Dry at 70℃, crush and sieve to obtain the finished product.

[0040] The finished product in this embodiment has a water absorption rate of 310 times for pure water and 81 times for physiological saline, with a biodegradation period of 165 days, making it suitable for water conservation applications in ordinary farmland.

[0041] Example 3

[0042] A green preparation process for a soybean straw-based multifunctional biodegradable water-retaining agent includes the following steps:

[0043] 1. Raw material pretreatment: Crush soybean straw through an 80-mesh sieve and dry it at 70℃ for 4 hours for later use.

[0044] 2. Green alkalization modification: solid-liquid ratio 1:12 (g / mL), pH adjusted to 11 with 4% sodium hydroxide solution, reacted at room temperature for 1.5 h, washed with water and dried.

[0045] 3. Graft polymerization reaction: 10g modified straw powder, 120mL deionized water, 60℃ water bath; add 25g acrylic acid, 12.5g acrylamide, and 0.3g composite initiator, and react for 2h.

[0046] 4. Crosslinking modification and functional compounding: Add 0.056g of crosslinking agent at 75℃ and crosslink for 45min; add 1.5g of potassium humate and 1.0g of bentonite for compounding modification.

[0047] 5. Post-processing and molding: Dry and pulverize at 80℃ to obtain the finished product.

[0048] The finished product in this embodiment has a water absorption rate of 485 times for pure water and 98 times for physiological saline. It has excellent salt and alkali resistance, a degradation cycle of 200 days, and is suitable for ecological restoration of saline-alkali land and desert.

Claims

1. A green preparation process for a soybean straw-based multifunctional biodegradable water-retaining agent, characterized in that, Includes the following steps: (1) Raw material pretreatment: Select dry soybean straw without mold, remove impurities, crush and pass through a 40-80 mesh sieve, dry at a constant temperature of 60-70℃ for 4-6 hours, and cool for later use; (2) Green alkalization modification: The pretreated straw powder is mixed with deionized water at a solid-liquid ratio of 1:8-1:12 (g / mL) to form a suspension. The pH value of the system is adjusted to 10-11 using a low concentration of sodium hydroxide solution. The mixture is stirred at room temperature for 1.5-2.5 h. After the reaction, the mixture is filtered, washed with water until neutral, and dried at 60℃ to obtain modified soybean straw powder. (3) Graft polymerization reaction: The modified soybean straw powder is dispersed in deionized water, heated to 50-60℃ in a water bath, and mixed monomers of acrylic acid and acrylamide are added. Then, a composite initiator is added, and the graft polymerization reaction is carried out at a constant temperature and stirred for 2-3 hours. (4) Crosslinking modification and functional compounding: Heat to 65-75℃, add N,N'-methylenebisacrylamide for crosslinking reaction for 30-45 min, then add potassium humate and bentonite for functional compounding, keep warm and stir for 20 min; (5) Post-processing molding: The reaction system is cooled to room temperature, dried at 70-80℃ to constant weight, crushed and sieved to obtain the soybean straw-based multifunctional biodegradable water-retaining agent.

2. The green preparation process of a soybean straw-based multifunctional biodegradable water-retaining agent according to claim 1, characterized in that: The mass concentration of the sodium hydroxide solution mentioned in step (2) is 2%-4%.

3. The green preparation process of a soybean straw-based multifunctional biodegradable water-retaining agent according to claim 1, characterized in that: The mass ratio of acrylic acid to acrylamide in step (3) is 2:1, and the total mass of the monomers is 2-4 times the mass of the modified soybean straw powder.

4. The green preparation process of a soybean straw-based multifunctional biodegradable water-retaining agent according to claim 1, characterized in that: The composite initiator mentioned in step (3) is a compound system of potassium persulfate and sodium bisulfite with a mass ratio of 3:

1. The total amount of initiator added is 0.3%-0.8% of the total mass of the monomer.

5. The green preparation process of a soybean straw-based multifunctional biodegradable water-retaining agent according to claim 1, characterized in that: The amount of N,N'-methylenebisacrylamide added in step (4) is 0.05%-0.15% of the total mass of the monomer.

6. The green preparation process of a soybean straw-based multifunctional biodegradable water-retaining agent according to claim 1, characterized in that: The amount of potassium humate added in step (4) is 8%-15% of the mass of the modified soybean straw powder, and the amount of bentonite added is 5%-10% of the mass of the modified soybean straw powder.

7. The green preparation process of a soybean straw-based multifunctional biodegradable water-retaining agent according to claim 1, characterized in that: In step (3), the water bath heating rate is 2℃ / min, and the stirring speed is controlled at 300-400r / min.

8. The soybean straw-based multifunctional biodegradable water-retaining agent prepared according to the process described in claim 1, characterized in that: The water-retaining agent has a water absorption rate of 300-500 times in pure water and ≥80 times in physiological saline. It can be completely biodegraded in soil within 160-200 days and has multiple functions including water retention, salt and alkali resistance, fertilizer retention, and soil improvement.