A fully biodegradable anti-sun type agricultural and forestry water-retaining agent and a preparation method thereof

Abstract

This invention discloses a fully biodegradable, sun-resistant water-retaining agent for agriculture and forestry, and its preparation method, aiming to solve the problems of insufficient salt tolerance, lack of anti-UV aging performance, uncontrollable degradation rate, and environmental residue risks of existing water-retaining agents. This water-retaining agent forms a three-dimensional network structure through free radical polymerization and cross-linking, consisting of an enzymatically hydrolyzable main chain component, a natural polysaccharide copolymerization reinforcing component, a salt-resistant modified component, a sun-resistant-enhancing synergistic component, and a responsive, controllable degradation component. Its preparation method includes raw material pretreatment, preparation of functionalized graphene, preparation of triple-responsive enzyme-carrying microspheres, polymerization reaction, and purification and drying steps. The water-retaining agent of this invention possesses salt tolerance, anti-UV aging, controllable degradation, and environmental friendliness, meeting the water retention needs of agriculture in saline-alkali land, while also having growth-promoting and soil microecological regulation functions.

Description

Technical Field

[0001] This invention relates to the field of water-retaining agents, specifically to a fully biodegradable, sun-resistant agricultural and forestry water-retaining agent and its preparation method. Background Technology

[0002] Traditional polyacrylic acid water-retaining agents have a high water absorption rate in pure water, but in saline soil environments, the water absorption capacity decreases sharply due to the ion shielding effect (the water absorption rate in 5% NaCl solution is usually <15 g / g). They are also difficult to be degraded by soil microorganisms. Long-term application can easily cause soil compaction, decreased porosity and microplastic pollution, which seriously restricts their application in saline-alkali land agriculture.

[0003] In recent years, polyamino acid materials have become a research hotspot due to their good biocompatibility and potential degradability. Among them, polyaspartic acid-based materials are considered a preferred alternative to polyacrylic acid materials. However, existing polyaspartic acid-based water-retaining agents have three major bottlenecks: First, insufficient salt tolerance, with water absorption rate dropping sharply to below 20 g / g in environments with >0.5% NaCl, failing to meet the water retention needs of saline-alkali land; second, lack of resistance to ultraviolet aging, easily causing main chain breakage under strong sunlight, leading to rapid failure of water retention function; and third, uncontrollable degradation rate, either degrading too quickly to guarantee the water retention needs of crops during their growth period, or degrading too slowly, still posing a risk of environmental residue.

[0004] To solve the above problems, existing technologies have made many attempts, but all of them have obvious defects: (1) Introducing carbon materials such as graphene to improve mechanical properties, but the problem of sun resistance and salt resistance synergy has not been solved. In addition, graphene has poor dispersibility and is easy to agglomerate, resulting in uneven internal structure of the material. At the same time, carbon materials are difficult to biodegrade, posing a risk of long-term environmental accumulation. (2) Using enzyme-controlled degradation strategy, but mostly non-specific enzymes such as lipase and amylase are selected, which are not compatible with the amide bond substrate of polyaspartic acid backbone, resulting in low degradation efficiency. In addition, the enzyme is easily deactivated by soil pH and metal ions. (4) Adding UV stabilizers alone, but inorganic UV stabilizers are difficult to degrade, causing secondary pollution to the environment. In addition, they have poor compatibility with organic gel networks, affecting water absorption performance.

[0005] In summary, existing technologies cannot simultaneously solve the four core problems in the application of saline-alkali land: salt tolerance, anti-aging under strong sunlight, controllable degradation matching crop growth period, and environmental friendliness. There is an urgent need to develop a multifunctional, synergistic, and balanced fully biodegradable water-retaining agent. Summary of the Invention

[0006] To address the problems of existing technologies, this invention provides a fully biodegradable sun-resistant water-retaining agent for agriculture and forestry and its preparation method.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A fully biodegradable, sun-resistant water-retaining agent for agriculture and forestry, wherein the water-retaining agent forms a three-dimensional network structure through free radical polymerization and cross-linking, and is composed of the following components, the proportion of each component being based on the total monomer mass:

[0009] The enzymatically hydrolyzable main chain component is a partially ring-opening polysuccinimide derivative, whose side chain contains carboxyl and secondary amine groups. The secondary amine groups can form Schiff base crosslinks with the aldehyde groups of natural polysaccharides and provide specific hydrolysis sites for proteases.

[0010] The natural polysaccharide copolymerization reinforcing component is corn cob hemicellulose that has undergone alkali extraction-ultrasound-assisted purification treatment, with an aldehyde content of 3.2–4.5 mmol / g after pretreatment. Alkali extraction-ultrasound-assisted purification refers to a process combining alkali extraction and ultrasound-assisted purification. The corn cob raw material is treated with an alkaline solution (such as sodium hydroxide solution). The glycosidic bonds in the hemicellulose molecules are easily broken under alkaline conditions, and components such as cellulose and lignin have low solubility in an alkaline environment, thus achieving preliminary separation of hemicellulose from other components. Ultrasound-assisted purification introduces ultrasonic treatment during the purification stage. Through the cavitation effect of ultrasound (the formation and instantaneous rupture of tiny bubbles in the liquid, generating local high temperature and pressure), the movement of solvent molecules is accelerated, promoting the dissolution of hemicellulose from residual impurities. Simultaneously, it can disrupt the hydrogen bonds between hemicellulose molecules, improving its dispersibility and purity, ultimately obtaining a high-purity high-quality hemicellulose.

[0011] The salt-resistant modified component, namely methacryloyloxyethyl betaine (SBMA), resists salt ion interference through the anti-polyelectrolyte effect;

[0012] The sun protection-enhancing synergistic component is composed of humic acid-lignin complex and 3,5-diaminobenzoic acid-functionalized reduced graphene oxide (DABA-rGO), in which the mass ratio of humic acid to lignin is 1:0.5–2. The two form a full-band UV protection synergistic system, and DABA-rGO can be absorbed by the environment.

[0013] The responsive and controllable degradation component is a carboxylated polylactic acid microsphere encapsulated with a thermophilic protease. The microsphere has a particle size of 1–10 μm and is loaded with polyethylene oxide-polypropylene glycol block copolymer (PEG-PPG-PEG). It can achieve a triple response of pH-temperature-humidity. When the ambient temperature is ≥45℃, the soil pH is ≤6.5 and the relative humidity is ≥60%, it releases a thermophilic protease that can specifically hydrolyze the amide bond of polysuccinimide derivative.

[0014] The crosslinking agent N,N'-methylenebisacrylamide (MBA) and the initiation system, wherein the initiation system is an ammonium persulfate / sodium bisulfite redox initiator pair;

[0015] The optimal ratio of each component of the water-retaining agent was determined by a performance-cost multi-objective optimization model. The model aims to minimize the raw material cost, with the following constraints: water absorption rate of 5% NaCl solution ≥70 g / g, water absorption retention rate after sun protection ≥85%, and degradation rate ≥95% after 28 days. The optimal ratio is 8 wt% methacryloyloxyethyl betaine, 0.1 mol% MBA, 0.2 wt% initiation system, and 3 wt% humic acid-lignin complex.

[0016] The preparation method of the fully biodegradable sun-resistant agricultural and forestry water-retaining agent includes the following steps:

[0017] (1) Raw material pretreatment: extraction and loading of corn cob hemicellulose: corn cob powder was passed through an 80-mesh sieve and extracted using cellulase method. The process parameters were: cellulase dosage 1.2–1.5 wt% (optimal 1.3 wt%), pH 4.8–5.2 (optimal 5.0), reaction temperature 48–52℃ (optimal 50℃), and constant temperature stirring for 3–4 h (optimal 3.5 h). This parameter range can reduce the enzyme preparation cost by 20% while ensuring a hemicellulose extraction rate of ≥85%, and no additional acid-base adjustment reagents are required, simplifying the process. After filtration, the filter residue was washed until neutral, filtered and dried to obtain high-quality hemicellulose. The high-quality hemicellulose was then added to IAA ethanol solution and Bacillus subtilis spore suspension (concentration 1×10⁻⁶). 9 "CFU / mL), IAA ethanol solution" refers to a solution formed by dissolving IAA (indoleacetic acid, a natural plant growth regulator) in ethanol. In this invention, it is used to load IAA onto corn cob hemicellulose. After stirring at room temperature for 2 hours, the mixture is filtered and dried to obtain a high-quality hemicellulose loaded with growth-promoting and microbial-regulating components. The Bacillus subtilis spores are surface-modified with 1% stearic acid ethanol solution to ensure that they are in a dormant state. Preparation of humic acid-lignin complex: Humic acid and alkali lignin are mixed at a mass ratio of 1:0.5–2, deionized water is added, and the mixture is ultrasonically dispersed at 300 W for 30 min. The pH is adjusted to 7.0, and the mixture is concentrated under reduced pressure to a solid content of 20% to obtain a humic acid-lignin complex dispersion.

[0018] (2) Preparation of 3,5-diaminobenzoic acid functionalized reduced graphene oxide (DABA-rGO): Graphene oxide was dispersed in deionized water at a preferred concentration of 0.5 mg / mL, and 3,5-diaminobenzoic acid (the mass ratio of graphene oxide to 3,5-diaminobenzoic acid was 1:5) was added. The mixture was stirred at room temperature for 12 h under EDC / NHS catalysis. In this scheme, "EDC / NHS" specifically refers to the condensation catalytic system composed of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS), which is the reagent combination used to promote the formation of covalent bonds in this invention. Then, ascorbic acid (twice the mass of graphene oxide) was added and reduced at 80°C for 2 h. After centrifugation and washing, the mixture was ultrasonically dispersed in deionized water to obtain an aqueous dispersion of 3,5-diaminobenzoic acid functionalized reduced graphene oxide (DABA-rGO) with a concentration of 0.5 mg / mL.

[0019] (3) Preparation of triple-response enzyme-carrying microspheres: Polylactic acid was dissolved in dichloromethane, maleic anhydride and PEG-PPG-PEG were added, and the mixture was stirred at 70℃ for 1 h. After cooling, thermophilic protease solution was added and ultrasonically emulsified to form an oil-in-water emulsion. The concentration of thermophilic protease solution was 10 mg / mL, and a total of 2 mL was added. The mixture was ultrasonically emulsified for 10 min (power 200 W) to form an oil-in-water emulsion. Then, 1% PVA solution (50 mL) was slowly added dropwise and stirred at room temperature for 4 h to volatilize the dichloromethane. The microspheres were collected by centrifugation and dispersed in 0.1 M NaOH solution. The mixture was stirred at 60℃ for 2 h to achieve ring-opening carboxylation of maleic anhydride. After adjusting the pH to 7.0, the microspheres were freeze-dried to obtain carboxylated modified enzyme-carrying PLA microspheres.

[0020] (4) Polymerization reaction: Mix partially open-ring polysuccinimide derivatives, hemicellulose concentrate loaded with growth-promoting and microbial regulation components, methacryloyloxyethyl betaine, humic acid-lignin composite dispersion, 3,5-diaminobenzoic acid functionalized reduced graphene oxide aqueous dispersion, triple-response enzyme-carrying microspheres, and N,N'-methylenebisacrylamide. After stirring evenly, purge with nitrogen for 30 min to remove oxygen. Add ammonium persulfate and sodium bisulfite, and react at 60℃ for 4 h to obtain a gel precursor. The hemicellulose concentrate loaded with growth-promoting and microbial regulation components specifically refers to corn cob hemicellulose material that has been extracted, purified, and loaded with plant growth regulators and functional microorganisms. It is the functionalized product of the "natural polysaccharide copolymerization reinforcing component" in this scheme. The concentrate is a functionalized natural polysaccharide material based on corn cob hemicellulose, loaded with growth-promoting components (IAA) and microbial regulation components (Bacillus subtilis spores) through a specific process. It accounts for 5-15% of the total monomer mass in the water-retaining agent. The wt% component mainly plays a role in enhancing network structure, synergistically promoting growth, and regulating soil microecology. The specific implementation method for this step is as follows: Using SBMA dosage (8 wt%, 14 wt%, 20 wt%), MBA dosage (0.05 mol%, 0.15 mol%, 0.3 mol%), initiation system dosage (0.2 wt%, 0.35 wt%, 0.5 wt%), and humic acid-lignin complex dosage (3 wt%, 6.5 wt%, 10 wt%) as factors, three levels were set for each. An orthogonal array was used for the experiment. The objective function was "Minimize Cost, constraints: 5% NaCl solution water absorption ≥70 g / g, water absorption retention rate after sun protection ≥85%, degradation rate ≥95% after 28 days". The optimal ratio was selected as SBMA 8 wt%, MBA 0.1 mol%, initiation system 0.2 wt%, and humic acid-lignin complex 3 wt%. Based on the optimal ratio selected by the orthogonal experiment, PSI (10 g), hemicellulose concentrate loaded with growth-promoting and microbial regulation components (1.2 g), and SBMA (0.8 g, 8 wt%) were dissolved in deionized water (60 mL) and stirred until completely dissolved. Humic acid-lignin complex dispersion (2 mL, 3 wt%), DABA-rGO dispersion (10 mL, containing 5 mg DABA-rGO, 0.05 wt%), triple-response enzyme-carrying PLA microspheres (0.3 g), and MBA (0.013 g, 0.1 mol%) were added. After stirring evenly, the mixture was transferred to a reaction vessel and purged with nitrogen for 30 min to remove oxygen. Ammonium persulfate (0.027 g) and sodium bisulfite (0.013 g) were added, with a total amount of 0.2 wt%. The mixture was reacted at 60℃ for 4 h to obtain the gel precursor.

[0021] In order to obtain a high-purity, structurally stable, and performance-compliant fully biodegradable sun-resistant agricultural and forestry water-retaining agent, this scheme adds a purification and drying step. The above purpose is achieved through the synergistic effect of "purification-drying". Specifically, (5) Purification and drying: The gel precursor is cut into small pieces of 1 cm × 1 cm × 1 cm and placed in a dialysis bag with a molecular weight cutoff of 8000–14000 Da for dialysis for 72 h (the deionized water is changed every 6 h). After dialysis, it is washed 3 times with deionized water and freeze-dried for 24 h under conditions of -50℃ and vacuum degree ≤10 Pa to obtain the finished product. The core purpose of the "purification and drying" step is to remove reaction residues and stabilize the three-dimensional network structure of the water-retaining agent. Specifically, it can be divided into the following two aspects:

[0022] First, purification is used to remove small molecule impurities and improve product purity. Dialysis removes unreacted components: using dialysis bags with a molecular weight cutoff of 8000–14000 Da, small molecules that did not participate in cross-linking during the polymerization reaction can be separated, such as residual monomers (e.g., SBMA, hemicellulose oligomers), initiators (ammonium persulfate / sodium bisulfite), unreacted cross-linking agents (MBA), and byproducts. Deionized water is replaced every 6 hours, and a concentration gradient is used to promote impurity diffusion, ensuring that soluble impurities are fully removed within 72 hours. Further purification through washing: After dialysis, the gel is washed three times with deionized water to physically remove trace impurities adhering to the gel surface, preventing residual substances from affecting the water absorption or biodegradability of the water-retaining agent. Secondly, drying: This fixes the network structure, resulting in a stable finished product. Freeze-drying prevents structural collapse: Under conditions of -50℃ low temperature and ≤10 Pa high vacuum, water sublimates directly from the solid state, avoiding gel network shrinkage and pore collapse caused by conventional heating and drying. This preserves the three-dimensional porous structure of the water-retaining agent, ensuring its high water absorption rate (≥70 g / g in 5% NaCl solution). Long-term storage stability: The dried finished product has extremely low water content, preventing microbial growth and component hydrolysis, facilitating long-term storage and transportation, while maintaining functional stability such as sun resistance and salt tolerance.

[0023] Compared with existing technologies, the beneficial effects of the invention are: the raw materials are widely available and have high industrialization feasibility, and the cost controllability is significantly improved: the raw materials such as corn cob hemicellulose and humic acid are all agricultural waste or natural minerals, which are abundant and inexpensive; the preparation process is simple, the room temperature polymerization has low energy consumption, and it is easy to carry out large-scale production and promotion.

[0024] Excellent salt tolerance and water absorption with controllable cost: The equilibrium water absorption rate in a 5% NaCl solution reaches 70–85 g / g (measured value 78–82 g / g). Even when the SBMA dosage is reduced to 8 wt%, the water absorption rate remains above 70 g / g, significantly superior to traditional polyacrylic acid water-retaining agents (<15 g / g) and existing polyaspartic acid-based water-retaining agents (20–35 g / g). In simulated saline-alkali soil leachate (containing Na⁺, Ca²⁺, Mg²⁺), the water absorption rate remains at 65–75 g / g, meeting the long-term water retention requirements of saline-alkali land. The minimum effective dosage of each component was determined through a performance-cost optimization model, reducing raw material costs by 15–20%.

[0025] Strong resistance to UV aging across the entire spectrum: simulated strong sunlight (1000) in a xenon lamp aging chamber. After 72 hours (equivalent to 30 days of natural sunlight), the water absorption rate remained ≥85% (measured value 85.4–88.2%), and the gel structure remained intact without breakage; while the control group (containing only humic acid or DABA-rGO) without the addition of sun-protective synergistic components had a water absorption rate of <60%, and traditional polyacrylic acid water-retaining agents only reached 40–45%;

[0026] Triple-response controlled degradation, precisely adapting to the natural environmental cycle: Through a triple-response mechanism of pH, temperature, and humidity, it achieves the regulatory goal of "stable growth period - precise degradation during rainfall." At 25℃, pH=7.0, and relative humidity <40% (drought environment), the degradation rate is <15% after 90 days, ensuring water retention throughout the crop's growth period; at 45℃, pH=6.0, and relative humidity ≥60% (post-rainfall environment), the degradation rate is ≥50% after 7 days, and the mineralization rate is ≥98% after 28 days; furthermore, after 90 days of soil burial, the residual amount of DABA-rGO is <0.01 mg / g of soil, achieving environmental absorption; the final degradation products are... It contains small molecule amino acids, which can be metabolized and utilized by soil microorganisms without leaving any environmental residues;

[0027] Balanced mechanical properties: tensile strength reaches 80–120 kPa, and compressive strength after swelling (swelling in 5% NaCl solution for 24 h) is ≥50 kPa, which is 40–60% higher than the control group without DABA-rGO. It can resist the extrusion of agricultural machinery and avoid structural damage.

[0028] It combines environmental friendliness, growth-promoting properties, and microecological regulation functions, achieving an upgrade from a "functional material" to a "soil microecological system regulator": all main components are bio-based or fully degradable materials, free of heavy metals, halogens, or non-degradable synthetic polymers; the loaded... Alternatively, IAA is slowly released through coordination and is protected by a gel network, resulting in excellent stability. This increases wheat seed germination rate by 10–15% and corn seedling height by 8–12%. Detailed Implementation

[0029] The present invention will be further described in detail below through embodiments. These embodiments are only used to illustrate the present invention and do not limit the scope of the present invention.

[0030] Example 1: Preparation of a fully biodegradable sun-resistant agricultural and forestry water-retaining agent. Raw material pretreatment, corn cob hemicellulose extraction: Take 100 g of corn cob powder (passed through an 80-mesh sieve), add cellulase solution (cellulase dosage 1.3 wt%, pH 5.0), stir at 50℃ for 3.5 h, filter to obtain filter residue; wash the filter residue with deionized water until pH=7.0, vacuum dry (60℃, 8 h), to obtain 19.2 g of hemicellulose concentrate, with an extraction rate of 89%; take 5 g of hemicellulose concentrate, add 5 mL of IAA ethanol solution (concentration 2 mg / mL) and 1 mL of Bacillus subtilis spore suspension (… Stirring at room temperature for 2 h, filtering and drying yielded a high-quality hemicellulose product loaded with growth-promoting and microbial-regulated components; Preparation of humic acid-lignin complex: 5 g of humic acid and 5 g of alkali lignin were added to 200 mL of deionized water, ultrasonically dispersed at 300 W for 30 min, the pH was adjusted to 7.0 with 1 M HAc, and concentrated under reduced pressure to a solid content of 20% to obtain a composite dispersion; Orthogonal experimental screening: using... An orthogonal array was used, with SBMA dosage, MBA dosage, initiation system dosage, and humic acid-lignin complex dosage as factors, and 5% NaCl water absorption rate, post-sun exposure retention rate, 28-day degradation rate, and raw material cost as evaluation indicators, to screen out the optimal ratio as 8 wt% SBMA, 0.1 mol% MBA, 0.2 wt% initiation system, and 3 wt% humic acid-lignin complex.

[0031] Preparation of DABA-rGO: Take 100 mg of GO, disperse it in 200 mL of deionized water, and sonicate for 30 min (300 W). Add 500 mg of 3,5-diaminobenzoic acid, stir to dissolve, and then add 600 mg of EDC. Stir and react at room temperature for 12 h. Add 200 mg of ascorbic acid, stir at 80 °C for 2 h, centrifuge (8000 rpm, 10 min) to collect the precipitate, wash it 3 times with deionized water, and sonicate it in 200 mL of deionized water to obtain DABA-rGO aqueous dispersion (0.5 mg / mL).

[0032] Preparation of pH-temperature-humidity triple-responsive enzyme-carrying microspheres: 100 mg PLA was dissolved in 5 mL of dichloromethane, 10 mg maleic anhydride and 8 mg PEG-PPG-PEG were added, and the mixture was stirred at 70 °C for 1 h. After cooling, 2 mL of thermophilic protease solution (10 mg / mL) was added, and the mixture was ultrasonically emulsified at 200 W for 10 min to form an oil-in-water emulsion. The emulsion was slowly added dropwise to 50 mL of 1% PVA solution, stirred at room temperature for 4 h, and the microspheres were collected by centrifugation (5000 rpm, 5 min). The microspheres were dispersed in 50 mL of 0.1 M NaOH solution, stirred at 60 °C for 2 h, and the pH was adjusted to 7.0 with 1 M HCl. The microspheres were then freeze-dried to obtain 115 mg of carboxylated modified PLA enzyme-carrying microspheres.

[0033] Polymerization reaction: 10 g PSI, 1.2 g hemicellulose concentrate loaded with growth-promoting and microbial-regulated components, and 0.8 g SBMA were dissolved in 60 mL deionized water and stirred until completely dissolved; 2 mL humic acid-lignin composite dispersion, 10 mL DABA-rGO dispersion, 0.3 g triple-responsive enzyme-carrying PLA microspheres, and 0.013 g MBA were added, stirred evenly, and then transferred to a 500 mL reactor. Nitrogen gas was purged for 30 min to remove oxygen; 0.027 g ammonium persulfate and 0.013 g sodium bisulfite were added, and the reaction was carried out at 60 °C for 4 h to obtain the gel precursor;

[0034] Purification and drying: The gel precursor was cut into 1 cm × 1 cm × 1 cm pieces and placed in a dialysis bag (molecular weight cutoff 8000–14000 Da) for dialysis for 72 h (with deionized water changed every 6 h); after dialysis, it was washed 3 times with deionized water and freeze-dried at -50℃ and vacuum degree ≤10 Pa for 24 h to obtain 12.5 g of fully biodegradable sun-resistant agricultural and forestry water-retaining agent.

[0035] This scheme uses a humic acid-lignin complex and a low amount of DABA-rGO to form a full-band UV-resistant synergistic system, solving the aging problem under strong sunlight. The zwitterionic SBMA and the carboxyl groups of polyaspartic acid derivatives form a salt-resistant synergistic effect, which improves salt resistance through anti-polyelectrolyte effect and ion repulsion effect. Thermosensitive PLA microspheres are modified with carboxylation and loaded with humidity-sensitive components. Combined with substrate matching design of specific thermophilic proteases, they realize a degradation "smart switch" that accurately links drought / rainfall cycles to achieve "water retention in drought and degradation in rain".

[0036] Example 2: Performance Testing

[0037] 1. Salt tolerance and water absorption rate test: According to GB / T 21620-2008 standard, tests were conducted in deionized water, 5% NaCl solution, and simulated saline-alkali soil extract (containing 0.5% NaCl). 0.1% 0.05% The water absorption rate of the samples was tested; the raw material cost per unit mass of the product was also calculated, and the results are shown in Table 1 below:

[0038] Table 1

[0039]

[0040] 2. UV aging resistance test: According to GB / T 16422.2-1999 standard, a xenon lamp aging chamber was used to simulate a strong solar radiation environment (1000 W / m², 72 h). The water absorption rate in 5% NaCl solution before and after aging was tested, and the retention rate was calculated. Control group 1 (without humic acid-lignin complex), control group 2 (without DABA-rGO), and control group 3 (traditional polyacrylic acid water-retaining agent) were set up. The results are shown in Table 2 below:

[0041] Table 2

[0042]

[0043] 3. Triple-response controllable degradation performance test: Soil degradation experiments were conducted according to ISO 17556-2003 standard. Three environmental gradients were set: 25℃ / pH=7.0 / 30% relative humidity, 45℃ / pH=7.0 / 60% relative humidity, and 45℃ / pH=6.0 / 60% relative humidity. The mass loss rate and DABA-rGO residue of samples at different time points were tested. The results are shown in Table 3 below:

[0044] Table 3

[0045]

[0046] 4. Mechanical property testing: The tensile strength of the samples was tested using a universal testing machine (model: CMT6104). The compressive strength was tested after swelling (swelling in 5% NaCl solution for 24 h). The results showed that the tensile strength was 102 kPa and the compressive strength after swelling was 60 kPa, which were 50% and 46% higher than the control group without DABA-rGO, respectively.

[0047] 5. Inorganic residue, ecotoxicity, and microecological regulation testing: 1) Inorganic residue: In the finished product, ICP-MS (model: Agilent 7900) was used for testing. Plasma content, the results show: Residual amount 3.0 ppm, Residual amount 1.7 ppm, 1) Residual amount: 2.3 ppm, all below the environmental standard of 10 ppm; 2) Ecotoxicity: Acute toxicity test of earthworms was conducted according to GB / T 31270.23-2014, with a 7-day survival rate of 98%; Soil microbial diversity test was conducted according to GB / T 4284-2018, and there was no significant difference in the Shannon index of the microbial community compared with the blank control group (P>0.05); 3) Microecological regulation: After 30 days of soil culture, the soil microbial community structure was analyzed using metagenomic sequencing technology (Illumina NovaSeq 6000 platform). The results showed that the colonization of Bacillus subtilis in the soil of the sample group of this invention reached 2.5×10⁻⁶. 6 CFU / g, the abundance of beneficial bacteria (nitrogen-fixing bacteria and phosphate-solubilizing bacteria) was significantly increased compared with the blank control group, with nitrogen-fixing bacteria abundance increasing by 45% and phosphate-solubilizing bacteria abundance increasing by 42%, while the abundance of harmful salt-tolerant bacteria (such as Halomonas) decreased by 30%; soil microbial community function prediction showed that the expression levels of functional genes related to nitrogen cycling and phosphorus cycling increased by 38% and 35%, respectively; 4) absorption of degradation products: wheat pot experiment showed that small molecule amino acids produced by degradation can be absorbed by wheat roots, and the nitrogen content in leaves increased by 6.2%.

[0048] 6. Growth-promoting performance test: Wheat was used as the test crop. The sample group of this invention (water-retaining agent to soil mass ratio 1:100), the water-retaining agent group without growth-promoting-microbial regulation component, and the blank control group were set up. The germination rate and plant height were measured 20 days after sowing. The results are shown in Table 4 below.

[0049] Table 4

[0050]

[0051] 7. Field trial data: A one-year field trial of maize planting was conducted in a plain saline-alkali land (soil EC value 8.5 mS / cm). The sample group of this invention (soil application before sowing, dosage 20 kg / mu), the traditional polyacrylic acid water-retaining agent group, and the blank control group were set up. The yield and soil EC value changes were measured. The results are shown in Table 5 below.

[0052] Table 5

[0053]

[0054] Example 3: Comparative Experiment (Creative Verification)

[0055] The following comparative groups were set up. Except for the difference in the specified components, the preparation methods were the same as those in Example 1. The water absorption rate in 5% NaCl solution, the water absorption rate retention rate after sun protection, the degradation rate after 28 days (45℃ / pH=6.0 / 60% humidity) and the wheat germination rate were tested. The results are shown in Table 6 below.

[0056] Table 6

[0057]

Claims

1. A fully biodegradable, sun-resistant, water-retaining agent for agriculture and forestry, characterized in that, The water-retaining agent forms a three-dimensional network structure through free radical polymerization and crosslinking, and is composed of the following components: Enzymatic hydrolysis of the main chain components; The natural polysaccharide copolymerization reinforcing component is corn cob hemicellulose that has undergone alkali extraction-ultrasound-assisted purification treatment. Salt-resistant modified component, wherein the salt-resistant modified component is methacryloyloxyethyl betaine, which resists salt ion interference through anti-polyelectrolyte effect; Humic acid-lignin complex and 3,5-diaminobenzoic acid functionalized reduced graphite oxide A synergistic anti-sunshine component composed of olefins; Response to controllable degradation components.

2. The fully biodegradable, sun-resistant, water-retaining agricultural and forestry agent according to claim 1, characterized in that, The mass ratio of humic acid to lignin in the humic acid-lignin complex is 1:0.5–2.

3. The fully biodegradable, sun-resistant, water-retaining agricultural and forestry agent according to claim 2, characterized in that, The responsive and controllable degradation component is a carboxylated polylactic acid microsphere containing a thermophilic protease.

4. A method for preparing a fully biodegradable, sun-resistant, water-retaining agricultural and forestry agent as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Raw material pretreatment includes: corn cob hemicellulose extraction and loading; preparation of humic acid-lignin complex; (2) Preparation of 3,5-diaminobenzoic acid functionalized reduced graphene oxide: Graphene oxide was dispersed in deionized water, 3,5-diaminobenzoic acid was added, the mixture was stirred at room temperature, ascorbic acid was added, and after centrifugation and washing, it was ultrasonically dispersed in deionized water to obtain an aqueous dispersion of 3,5-diaminobenzoic acid functionalized reduced graphene oxide. (3) Preparation of triple-response enzyme-carrying microspheres: Polylactic acid was dissolved in dichloromethane, maleic anhydride and PEG-PPG-PEG were added, and the mixture was stirred at 70°C for 1 h. After cooling, thermophilic protease solution was added and ultrasonically emulsified to form an oil-in-water emulsion. Then, 1% PVA solution was slowly added and stirred at room temperature for 4 h to volatilize the dichloromethane. The microspheres were collected by centrifugation and dispersed in 0.1 M NaOH solution. The mixture was stirred at 60°C for 2 h to achieve ring-opening carboxylation of maleic anhydride. After adjusting the pH to 7.0, the microspheres were freeze-dried. (4) Polymerization reaction: Mix partially open-ring polysuccinimide derivatives, hemicellulose loaded with growth-promoting and microbial regulation components, methacryloyloxyethyl betaine, humic acid-lignin composite dispersion, 3,5-diaminobenzoic acid functionalized reduced graphene oxide aqueous dispersion, triple-response enzyme-carrying microspheres and N,N'-methylenebisacrylamide, stir evenly, then purge with nitrogen for 30 min to remove oxygen, add ammonium persulfate and sodium bisulfite, and react at 60℃ for 4 h to obtain gel precursor; (5) Purification and drying: Cut the gel precursor into small pieces of 1 cm × 1 cm × 1 cm, place them in a dialysis bag with a molecular weight cutoff of 8000–14000 Da and dialyze for 72 h. After dialysis, wash with deionized water 3 times and freeze dry for 24 h at -50℃ and vacuum degree ≤10 Pa to obtain the finished product.

5. The preparation method of the fully biodegradable sun-resistant agricultural and forestry water-retaining agent according to claim 4, characterized in that, In step (1), corn cob powder is passed through an 80-mesh sieve and extracted using cellulase. After filtration, the residue is washed until neutral and then filtered and dried to obtain a high-quality hemicellulose. The high-quality hemicellulose is then taken, and IAA ethanol solution and Bacillus subtilis spore suspension are added. The mixture is stirred at room temperature, filtered, and dried to obtain a high-quality hemicellulose loaded with growth-promoting and microbial regulation components.

6. The preparation method of the fully biodegradable sun-resistant agricultural and forestry water-retaining agent according to claim 5, characterized in that, In step (1), humic acid and alkali lignin are mixed at a mass ratio of 1:0.5–2, deionized water is added, and ultrasonic dispersion is performed at 300 W for 30 min. The pH is adjusted to 7.0, and the mixture is concentrated by vacuum distillation to a solid content of 20% to obtain a humic acid-lignin composite dispersion.

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