A biomimetic lignin-based saline-alkali soil improvement material and a preparation method thereof

Abstract

The application discloses a kind of bionic lignin-based saline-alkali land improvement materials and preparation method, belong to polymer material and soil improvement technical field.The saline-alkali land improvement material of the present application uses lignin or its derivative as skeleton, simulates the charge distribution of wheat glutelin and the sodium ion response function of dynamic disulfide bond, and through step-by-step activation and alternating copolymerization in aqueous solution polymerization reaction system, the sequence and proportion of sulfonic acid group and quaternary ammonium salt group segment are accurately controlled, so that positive and negative charges form more uniform sequence distribution, realize the amphiphilicity of lignin compound;Then introduce thiol group using click chemistry and realize the linear regulation of material viscosity and water-soluble using the chain transfer characteristics of multi-thiol functional group, to meet the needs of different saline-alkali land application scenarios.The present application breaks through the limitation of traditional lignin product single function, realizes the efficient use of lignin, and develops high stability, pH and Na + The application discloses a kind of bionic lignin-based saline-alkali land improvement materials and preparation method, belong to polymer material and soil improvement technical field.The saline-alkali land improvement material of the present application uses lignin or its derivative as skeleton, simulates the charge distribution of wheat glutelin and the sodium ion response function of dynamic disulfide bond, and through step-by-step activation and alternating copolymerization in aqueous solution polymerization reaction system, the sequence and proportion of sulfonic acid group and quaternary ammonium salt group segment are accurately controlled, so that positive and negative charges form more uniform sequence distribution, realize the amphiphilicity of lignin compound;Then introduce thiol group using click chemistry and realize the linear regulation of material viscosity and water-soluble using the chain transfer characteristics of multi-thiol functional group, to meet the needs of different saline-alkali land application scenarios.The present application breaks through the limitation of traditional lignin product single function, realizes the efficient use of lignin, and develops high stability, pH and Na + Multiple environment response integrated intelligent saline-alkali soil improvement material.

Description

Technical Field

[0001] This invention relates to the fields of polymer materials and soil improvement technology, specifically to a biomimetic lignin-based saline-alkali land improvement material and its preparation method. Background Technology

[0002] Soil salinization is a significant manifestation of soil degradation, posing serious threats to agricultural production, ecological security, and human health. The core challenge in improving saline-alkali soils lies in excessive sodium ions and high pH levels. These conditions easily lead to soil compaction, reduced aeration and permeability, nutrient imbalance, and ion toxicity and osmotic stress on plant growth.

[0003] In high-salt environments, a large number of cations can shield the electrostatic interaction between polymeric soil conditioners and soil particles, significantly reducing their charge neutralization and bridging capabilities. High pH conditions inhibit the ionization of some functional groups, reducing their effective radius of action and rendering them ineffective. Simultaneously, saline-alkali land commonly experiences alternating wet and dry processes of "drought-induced salinization" and "rainy season leaching." Water-retaining agents such as polyvinyl alcohol cannot inhibit water evaporation during droughts, leading to salt accumulation on the surface. While some desalination-type polymeric conditioners, such as carboxyl-grafted natural polysaccharides, can adsorb sodium ions through ion exchange, they are easily leached away by rainwater during the rainy season, resulting in "salinization after desalination."

[0004] To overcome this bottleneck, a smart saline-alkali land improvement material is needed that combines high stability under saline-alkali conditions with environmental responsiveness. Natural polymers, due to their wide availability, ease of functional modification, and biodegradability, have become rational substrates. Lignin, as a natural three-dimensional polymer with abundant reserves and low cost, suffers from structural heterogeneity and inhomogeneity, low reactivity and complex functional groups, and poor solubility and compatibility, limiting its efficient utilization. Currently, lignin modification methods for water-retaining agents, flocculants, and soil conditioners mostly employ simple mixed copolymerization methods. For example, patent (CN115772267A) reacts lignin sulfonate with quaternary ammonium salts and then crosslinks it with polyvinyl alcohol to obtain a zwitterionic emulsion, whose main functions are water retention and sand particle adhesion. Patent (CN112537989A) prepares a hydrophilic resin by copolymerizing lignin sulfonate with anionic acrylic acid, humic acid, etc.; the polymerization reaction is a mixed polymerization, and the material itself is insoluble in water. Both methods focus on water retention and have a single charge type, making it difficult to achieve charge neutralization and metal ion exchange in saline-alkali soil through the synergistic effect of high-density positive and negative charges. Another patent (CN113831480A) modifies lignin with itaconic acid and quaternary ammonium salt cations, utilizing their charge neutralization effect as a demulsifier for crude oil wastewater. However, itaconic acid contains two carboxyl groups in its molecular structure, which easily form steric hindrance, reducing its grafting efficiency onto lignin. Furthermore, the carboxylic acid groups are easily affected by Cl in the high-salt environment of saline-alkali soil. - SO42- The iso-ion effect inhibits dissociation, leading to a decrease in charge neutralization capacity. Furthermore, the aforementioned materials cannot precisely control polymer polarity through molecular regulation and lack sodium ion responsiveness, making them unsuitable for saline-alkali land improvement. Patent (CN120459954A) describes a gel formed by crosslinking lignin modified with acetic acid-hydrogen peroxide with acrylic acid for use as an adsorbent for sodium ions in saline-alkali land. However, this material cannot sense dynamic changes in soil sodium ion concentration, lacks responsiveness, and affects the precision and sustainability of its adsorption. Moreover, this gel primarily focuses on sodium ion removal, failing to simultaneously improve soil aggregates and structure, resulting in a limited function that is insufficient to meet the comprehensive improvement needs of saline-alkali land. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a biomimetic lignin-based saline-alkali land improvement material and its preparation method. This invention innovatively mimics the balanced positive and negative charge distribution of glutenin and the self-repairing function of sodium ions in disulfide bonds, developing a saline-alkali land improvement material that integrates lignin's pH and sodium ion environmental response with a synergistic repair mechanism.

[0006] This invention first provides a method for preparing lignin-based saline-alkali land improvement materials, which includes the following steps:

[0007] Lignin and / or lignin derivatives are modified by aqueous solution polymerization with sulfonic acid anionic monomers and quaternary ammonium salt cationic monomers to obtain an amphiphilic anionic-cationic lignin composite system solution. By introducing polythiol monomers using click chemistry, lignin-based saline-alkali soil improvement materials are prepared.

[0008] In the above preparation method, the lignin derivative is at least one of calcium lignin sulfonate, sodium lignin sulfonate, magnesium lignin sulfonate, potassium lignin sulfonate, ammonium lignin sulfonate, alkali lignin, sulfate lignin, groundwood lignin, alkylated lignin, aminoated lignin, hydroxymethylated lignin, acetylated lignin, and oxidized lignin.

[0009] The sulfonic acid anionic monomer is at least one of 2-acrylamido-2-methylpropanesulfonic acid, acrylamide tert-butylsulfonic acid, 2-(methacryloyloxy)ethyldimethyl-(3-sulfopropyl)ammonium hydroxide, sulfopropyl methacrylate, sodium methpropylene sulfonate, sodium propylene sulfonate, sodium 3-allyloxy-2-hydroxypropanesulfonate, potassium 3-sulfopropyl acrylate, potassium sulfopropyl methacrylate, sodium vinyl sulfonate, and sodium p-styrene sulfonate.

[0010] The quaternary ammonium salt cationic monomer is at least one of the following: methacryloyloxyethyltrimethylammonium chloride, dimethyl diallyl ammonium chloride, acryloyloxyethyltrimethylammonium chloride, methacrylamidopropyltrimethylammonium chloride, benzylvinyltrimethylammonium chloride, methacryloyloxyethyldimethylbenzylammonium chloride, N-decyl-N,N-dimethylbenzylammonium chloride, 2-acrylamidoethyldimethyldodecylammonium bromide, allyltrimethylammonium chloride, and hydroxypropyltrimethylammonium chloride chitosan;

[0011] The polythiol monomer is at least one of trimethylolpropane tris(3-mercaptopropionic acid), pentaerythritol tetra(3-mercaptopropionic acid) ester, ethylene glycol di(3-mercaptopropionate), trimethylolpropane tris(2-mercaptoacetate), pentaerythritol tetramercaptoacetate, and dipentaerythritol hexa(3-mercaptopropionate).

[0012] The preparation method specifically includes the following steps: S1, adjusting the pH value of the lignin and / or lignin derivative solution and heating; dividing the quaternary ammonium salt cationic monomer solution into two equal parts by volume, and adding one part to the lignin and / or lignin derivative solution; dividing the oxidant and reducing agent solutions into three equal parts by weight, adding one part of the oxidant solution to the above solution, and then adding one part of the reducing agent solution, and reacting;

[0013] S2. Divide the sulfonic acid anion monomer solution into two equal parts by volume. Add one part of the sulfonic acid anion monomer solution to the system obtained in S1 and react. Then add the other part of the quaternary ammonium salt cationic monomer solution, add one part of the oxidant solution, add one part of the reducing agent solution, and finally add the other part of the sulfonic acid anion monomer solution and react. The resulting anion-cationic lignin composite system solution is obtained.

[0014] S3. Mix the multi-thiol monomer solution and the anion-cationic lignin composite system solution, add one part of oxidant solution and then one part of reducing agent solution, react, and after drying, obtain the lignin-based saline-alkali land improvement material.

[0015] In the above preparation method, the mass percentage concentration of the lignin and / or lignin derivative is 5%-35%;

[0016] The solvent for the lignin and / or lignin derivatives is water;

[0017] The quaternary ammonium salt cationic monomer solution has a mass percentage concentration of 60%-80%; the solvent for the quaternary ammonium salt cationic monomer solution is water.

[0018] The oxidant is at least one of ammonium persulfate, potassium persulfate, sodium persulfate, and hydrogen peroxide;

[0019] The reducing agent is at least one of ascorbic acid, sodium bisulfite, sodium sulfite, and sodium thiosulfate;

[0020] The mass percentage concentration of the oxidant and reducing agent solution is 3%-15%; preferably 5%-10%.

[0021] The sulfonic acid anion monomer solution has a mass percentage concentration of 30%-65%; the solvent for the sulfonic acid anion monomer solution is water.

[0022] The mass percentage concentration of the polythiol monomer solution is 3.5%-30%; the solvent of the polythiol monomer solution is an ethanol solution.

[0023] The ratio of the total mass of the sulfonic acid anionic monomer and the quaternary ammonium salt cationic monomer to the mass of the lignin and / or lignin derivative is 2-16:1;

[0024] The mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is 1:8 to 8:1;

[0025] The total mass of the oxidizing agent and reducing agent is 0.5%-5% of the total mass of the lignin and / or lignin derivatives, quaternary ammonium cationic monomers, sulfonic acid anionic monomers, and polythiol monomers; preferably 1%-2%.

[0026] The mass ratio of the oxidant to the reducing agent is 1:1-1.5;

[0027] The mass ratio of lignin and / or lignin derivatives to polythiol monomers is 5-15:1.

[0028] In the above preparation method, when the mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is in different ranges, the lignin-based saline-alkali soil improvement material exhibits drastically different macroscopic physical states:

[0029] When the mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is 1:1.5 to 1.5:1, the lignin-based saline-alkali soil improvement material forms a stretchable gel state.

[0030] When the mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is between 1:1.5 and 1:8 (excluding 1:1.5), the lignin-based saline-alkali soil improvement material forms a high-viscosity aqueous solution.

[0031] When the mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is between 1.5:1 and 8:1 (excluding 1.5:1), the lignin-based saline-alkali soil improvement material forms a low-viscosity aqueous solution.

[0032] In the above preparation method, in step S1, the pH of the lignin and / or lignin derivative solution is adjusted to 10-12 using KOH solution;

[0033] The heating temperature is 35-50℃; preferably 40℃-45℃.

[0034] The reaction time is 1-2 hours;

[0035] In step S2, a portion of sulfonic acid anionic monomer solution is added to the system obtained in S1, and the reaction time is 1-2 hours.

[0036] After adding another portion of the sulfonic acid anion monomer solution, the reaction time is 1-2 hours.

[0037] In step S3, the reaction time is 2-4 hours.

[0038] In the above preparation method, in steps S1, S2 and S3, the oxidant solution is added dropwise for 30 minutes and then the reducing agent solution is added dropwise.

[0039] In step S3, the multi-thiol monomer solution is added dropwise to the anion-cation lignin composite system solution at a flow rate of 0.5-15 mL / min.

[0040] The present invention also provides lignin-based saline-alkali land improvement materials prepared by the above preparation method.

[0041] The application of the aforementioned lignin-based saline-alkali soil amendment materials in improving saline-alkali soils also falls within the scope of protection of this invention.

[0042] Specifically, the saline-alkali soil has one or more of the following properties:

[0043] (1) High pH value: The soil pH value is usually greater than 8.5, and can even reach 9.0 or above, which is strongly alkaline;

[0044] (2) High exchangeable sodium content: The proportion of sodium ions adsorbed on soil colloids is relatively high, and the sodium adsorption ratio is usually greater than 13, which leads to the dispersion of soil particles.

[0045] (3) Deterioration of soil structure: Due to the dispersing effect of sodium ions, the soil aggregate structure is destroyed, resulting in compaction and poor water permeability and air permeability.

[0046] (4) Ion poisoning and nutrient imbalance: Excessive sodium ions, chloride ions, carbonate / bicarbonate ions in the soil solution directly poison the plant roots and inhibit the absorption of essential nutrients such as calcium and potassium.

[0047] In the above applications, based on the different mass ratios of the sulfonic acid anionic monomer and the quaternary ammonium salt cationic monomer, and the lignin-based saline-alkali soil improvement material obtained after reaction with the polythiol monomer, the following application methods and dosages are adopted:

[0048] 1) When the mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is 1:1.5 to 1.5:1, it can be applied directly to the soil as a soil conditioner or used as a coating material; wherein, the application rate of the soil conditioner is 40-200 kg / mu, and the application rate of the coating material is 3%-20% of the total mass of the coating fertilizer.

[0049] 2) When the mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is 1:8 to 1:1.5, the resulting material is prepared as an aqueous solution for foliar spraying or drip irrigation; for foliar spraying, the concentration is prepared at 0.5%-2% and the dosage is 20-50 kg / mu, and for drip irrigation, the concentration is prepared at 0.01-2% and the dosage is 20-150 kg / mu.

[0050] 3) When the mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is between 1.5:1 and 3:1, the resulting material is used as a root-dipping agent for seedlings. When using it, dilute it to a mass concentration of 0.1% to 0.3%, soak the crop roots in the solution for 5 minutes, and then plant it.

[0051] The biomimetic lignin-based saline-alkali land improvement material of this invention has the following innovative design:

[0052] (1) In the aqueous polymerization reaction system, the sequence and ratio of sulfonic acid groups and quaternary ammonium salt groups are precisely controlled by step activation and alternating copolymerization to make the positive and negative charges form a more uniform sequence distribution, and an amphiphilic ionic polymer with adjustable anion and cation ratio is prepared.

[0053] (2) By leveraging the regulatory effect of anions and cations on the polarity of lignin, thiol groups are encouraged to achieve confinement and regular arrangement, thereby efficiently completing the thiol-alkene click chemical reaction and introducing multifunctional thiol monomers; at the same time, the chain transfer characteristics of multi-thiol functional groups are used to adjust the degree of crosslinking of materials to meet the needs of different application scenarios.

[0054] (3) Polythiol groups can shield the surface charge of materials under high sodium ion concentration, reduce electrostatic repulsion, allow chains to approach and oxidize to generate dynamic disulfide bonds, initiate polymer cross-linking to fix sodium ions, and reduce soil salinity;

[0055] (4) The sulfonic acid group maintains a stable negative charge to adsorb ions in the soil, and the quaternary ammonium salt group can effectively flocculate negatively charged clay particles. In a high saline-alkali environment, it maintains excellent charge neutralization and bridging ability and can achieve a significant and reversible conformational change response behavior of the material in the pH range of 5 to 11.

[0056] In summary, the innovation of this invention lies in the design and preparation of a lignin-based material that possesses pH and Na+ properties. + A smart, biomimetic saline-alkali land improvement material with dual-response capabilities. This design ultimately translates into two key applications, achieving synergistic improvement. Specifically, the advantages of this invention are as follows: the quaternary ammonium salt groups can efficiently neutralize and flocculate negatively charged soil clay particles, and the sulfonic acid groups, through Na... + The displacement process reduces soil salinity, while the long polymer chains act as bridging agents, linking fine particles into stable, larger particles. This "neutralization-bridging" process effectively promotes the formation of soil aggregates, breaks up compaction, fundamentally improves soil physical structure, and accelerates soil salt leaching and alkalinity removal; in high Na+ soils... + Under certain conditions, the oxidation of polythiol groups generates dynamic disulfide bonds, which not only crosslink and fix free Na+, but also... + It reduces soluble salt content in soil and promotes the formation of large aggregates through bridging networks. The material exhibits reversible conformational changes in the pH range of 5-11 and can intelligently regulate charge exposure and cross-linking behavior according to changes in the microenvironment of saline-alkali land, ensuring that it can continuously play the role of aggregate construction and salt regulation in areas with different salinity intensities. Attached Figure Description

[0057] Figure 1 The synthesis process of CaLS-AMPS / DMC / TMPMP prepared in Example 1.

[0058] Figure 2 The dynamic disulfide bond formation principle of CaLS-AMPS / DMC / TMPMP prepared in Example 1.

[0059] Figure 3 The image shows the pH and sodium ion response morphology changes of the CaLS-AMPS / DMC / TMPMP prepared in Example 1.

[0060] Figure 4 Macroscopic and SEM images of the CaLS-AMPS / DMC / TMPMP prepared in Examples 1-3.

[0061] Figure 5 Infrared spectra of CaLS, DMC and CaLS-AMPS / DMC / TMPMP prepared in Example 1.

[0062] Figure 6 The image shows the pH-responsive macroscopic morphology of CaLS-AMPS / DMC / TMPMP prepared in Examples 1-2.

[0063] Figure 7 The images show the macroscopic morphology of the sodium ion responsive CaLS-AMPS / DMC / TMPMP prepared in Examples 1-2.

[0064] Figure 8 The images show the soil flocculation effect of the saline-alkali land improvement materials prepared in Examples 1-3 and Comparative Examples 1-5.

[0065] Figure 9 This is a comparison chart of the leaching volume and infiltration time of soil columns under different treatment conditions.

[0066] Figure 10 The effects of lignin-based saline-alkali soil amendments on the properties of potted soil. Detailed Implementation

[0067] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0068] Unless otherwise specified, the experimental methods described in the following examples are conventional methods.

[0069] Unless otherwise specified, the quantitative experiments in the following examples are all repeated three times, and the results are averaged.

[0070] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0071] Example 1

[0072] Prepare 500 mL of a 10% (w / w) calcium lignosulfonate (CaLS) solution (deionized water as solvent), then transfer it to a reactor. Adjust the pH of the calcium lignosulfonate solution to 10.3 with 1M KOH solution, heat to 45°C, and continuously purge with nitrogen for 30 min. Add 67 mL of 75 wt% DMC solution (methacryloyloxyethyltrimethylammonium chloride, water as solvent) dropwise to the reaction system. Dissolve 1.6 g of ammonium persulfate (oxidant) and 1.6 g of ascorbic acid (reducing agent) in 30 mL of deionized water, and divide each solution into three equal portions. First, add one portion of the ammonium persulfate solution dropwise to the reactor. After 30 min, add one portion of the ascorbic acid solution. React for 1.5 h. Add 50 g of... 2-Acrylamido-2-methylpropanesulfonic acid (AMPS) was dissolved in 100 mL of deionized water. 50% of the total volume of the prepared AMPS solution was added to the reactor, and the reaction was allowed to proceed for 1.5 h. 67 mL of 75 wt% DMC solution (methacryloyloxyethyltrimethylammonium chloride, water as solvent) was added to the system, followed by dropwise addition of one part of ammonium persulfate solution. After 30 min, one part of ascorbic acid solution was added dropwise, and the remaining AMPS solution was added to the system. The reaction was allowed to proceed for 1.5 h to obtain an anionic-cationic lignin composite system solution. 5 g of trimethylolpropane tris(3-mercaptopropionic acid) was dissolved in 70 mL of 95% (v / v) ethanol solution to obtain a trimethylolpropane tris(3-mercaptopropionic acid) solution. Then, the solution was reacted at a flow rate of 2... The solution of trimethylolpropane tris(3-mercaptopropionic acid) was added dropwise at a rate of mL / min to the above solution, followed by the addition of the remaining ammonium persulfate solution. After 30 min, the remaining ascorbic acid solution was added dropwise, and the experiment was terminated after 2.5 h of reaction. The mixture after the above reaction was cooled to room temperature and dried in an oven at 60 °C to obtain the biomimetic lignin-based saline-alkali soil improvement material (CaLS-AMPS / DMC / TMPMP).

[0073] Example 2

[0074] The preparation method is the same as in Example 1, except that "67 mL of 75 wt% DMC solution" in Example 1 is replaced with "34 mL of 75 wt% DMC solution", "50 g AMPS" is replaced with "100 g AMPS", "70 mL of 95% anhydrous ethanol" is replaced with "20 mL of 95% anhydrous ethanol", and "added dropwise to the above solution at a flow rate of 2 mL / min" is replaced with "added dropwise to the above solution at a flow rate of 0.7 mL / min".

[0075] Example 3

[0076] The preparation method is the same as in Example 1, except that "67 mL of 75 wt% DMC solution" in Example 1 is replaced with "62.5 mL of 80 wt% DAC solution (acryloyloxyethyltrimethylammonium chloride, solvent is water)"; "50 g AMPS" is replaced with "100 g AMPS"; "70 mL of 95% anhydrous ethanol" is replaced with "45 mL of 95% anhydrous ethanol"; and "added dropwise to the above solution at a flow rate of 2 mL / min" is replaced with "added dropwise to the above solution at a flow rate of 1.5 mL / min".

[0077] Comparative Example 1

[0078] The comparative example uses the same types and qualities of raw materials as Example 1, with the main difference being that alternating copolymerization is not performed. At the start of the reaction, CLS, AMPS, and DMC are simultaneously added to the reactor. The oxidant and reductant are added to the reaction system in three separate additions, each 1.5 hours apart.

[0079] The specific preparation method is as follows:

[0080] Prepare 500 mL of a 10% (w / w) calcium lignosulfonate (CaLS) solution and transfer it to a reactor. Adjust the pH of the calcium lignosulfonate solution to 10.3 with 1M KOH solution, heat to 45°C, and continuously purge with nitrogen for 30 min. Add 134 mL of a 75 wt% DMC solution (methacryloyloxyethyltrimethylammonium chloride, water as solvent) dropwise to the reaction system, and then add 50 g of... 2-Acrylamido-2-methylpropanesulfonic acid (AMPS) was dissolved in 100 mL of deionized water and added to the above reaction system. 1.6 g of oxidant ammonium persulfate and 1.6 g of reducing agent ascorbic acid were dissolved in 30 mL of deionized water, and divided into three equal portions by weight. One portion of the ammonium persulfate solution was added dropwise to the reactor, followed by one portion of the ascorbic acid solution after 30 min, and the reaction was allowed to proceed for 1.5 h. Another portion of the ammonium persulfate solution was added dropwise, followed by one portion of the ascorbic acid solution after 30 min, and the reaction was allowed to proceed for 1.5 h, yielding an anionic-cationic lignin composite system solution. 5 g of trimethylolpropane tris(3-mercaptopropionic acid) ester was dissolved in 70 mL of 95% (v / v) ethanol solution to obtain a trimethylolpropane tris(3-mercaptopropionic acid) ester solution, which was then reacted at a flow rate of 2... The solution of trimethylolpropane tris(3-mercaptopropionic acid) was added dropwise at a rate of ml / min to the above solution, followed by the addition of the remaining ammonium persulfate solution. After 30 min, the remaining ascorbic acid solution was added dropwise, and the experiment was terminated after 2.5 h of reaction. The mixture after the above reaction was cooled to room temperature and dried in an oven at 60 °C to obtain lignin-based saline-alkali soil improvement material.

[0081] Comparative Example 2

[0082] The comparative example uses the same types and qualities of raw materials as Example 1. The main difference in process is that stepwise activation is not performed. When the temperature in the initial reaction system is raised to 45°C, ammonium persulfate (oxidant) and ascorbic acid (reducing agent) are added directly.

[0083] The specific preparation method is as follows:

[0084] Prepare 500 mL of a 10% calcium lignosulfonate (CaLS) solution and transfer it to a reactor. Adjust the pH of the calcium lignosulfonate solution to 10.3 with 1M KOH solution. Heat to 45°C and continuously purge with nitrogen for 30 min. Add 67 mL of 75 wt% DMC solution (methacryloyloxyethyltrimethylammonium chloride, water as solvent) dropwise to the reaction system. Dissolve 1.6 g of ammonium persulfate (oxidant) and 1.6 g of ascorbic acid (reducing agent) in 30 mL of deionized water. First, add the ammonium persulfate solution dropwise to the reactor, followed by the ascorbic acid solution after 30 min. React for 1.5 h. Dissolve 50 g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) in 100 mL of deionized water. Measure 50% of the total volume of the prepared AMPS solution and add it to the reactor. React for 1.5 h. Add 67 mL of 75 wt% DMC solution to the system. The DMC solution (methacryloyloxyethyltrimethylammonium chloride, solvent: water) was then added to the system, followed by the addition of the remaining AMPS solution. The reaction was carried out for 1.5 h to obtain an anionic-cationic lignin composite system solution. 5 g of trimethylolpropane tris(3-mercaptopropionic acid) ester was dissolved in 70 mL of 95% (v / v) ethanol solution to obtain a trimethylolpropane tris(3-mercaptopropionic acid) ester solution. The trimethylolpropane tris(3-mercaptopropionic acid) ester solution was then added dropwise to the above solution at a flow rate of 2 mL / min. The reaction was carried out for 2.5 h to end the experiment. The mixture after the above reaction was cooled to room temperature and dried in a 60 °C oven to obtain lignin-based saline-alkali soil improvement material.

[0085] Comparative Example 3

[0086] The difference between this comparative example and Example 1 is that AMPS was replaced with the same mass of itaconic acid. Other preparation methods and raw materials are the same as in Example 1.

[0087] Comparative Example 4

[0088] The difference between this comparative example and Example 1 is that the sulfonic acid group anionic monomer solution is not introduced, but only the quaternary ammonium salt cationic monomer solution is introduced.

[0089] The specific preparation steps are as follows:

[0090] Prepare 500 mL of a 10% calcium lignosulfonate (CaLS) solution and transfer it to a reactor. Adjust the pH of the mixture to 10.3 with 1M KOH solution, heat to 45°C, and continuously purge with nitrogen for 30 min. Add 134 mL of 75 wt% DMC solution (methacryloyloxyethyltrimethylammonium chloride, water as solvent) dropwise to the reaction system. Dissolve 1.6 g of ammonium persulfate and 1.6 g of ascorbic acid, the reducing agent, in 30 mL of deionized water, and divide each solution into three equal portions. First, add one portion of the ammonium persulfate solution dropwise to the reactor. After 30 min, add the other portion of the ascorbic acid solution. React for 1.5 h. Add 134 mL of 75 wt% DMC solution to the system. DMC solution (methacryloyloxyethyltrimethylammonium chloride, solvent: water) was added dropwise with one part of ammonium persulfate solution. After 30 min, one part of ascorbic acid solution was added dropwise, and the reaction was carried out for 1.5 h to obtain a lignin copolymer system solution. 5 g of trimethylolpropane tris(3-mercaptopropionic acid) ester was dissolved in 70 mL of 95% ethanol solution to obtain a trimethylolpropane tris(3-mercaptopropionic acid) ester solution. Then, the trimethylolpropane tris(3-mercaptopropionic acid) ester solution was added dropwise to the above lignin copolymer system solution, followed by the addition of the remaining ammonium persulfate solution. After 30 min, the remaining ascorbic acid solution was added dropwise, and the reaction was carried out for 2.5 h to end the experiment. The mixture after the above reaction was cooled to room temperature and dried in an oven at 60 °C to obtain a lignin-based saline-alkali soil improvement material.

[0091] Comparative Example 5

[0092] The difference between this comparative example and Example 1 is that a quaternary ammonium salt cationic monomer solution is not introduced; only a sulfonic acid anionic monomer solution is introduced.

[0093] The specific preparation steps are as follows:

[0094] Prepare 500 mL of a 10% (w / w) calcium lignosulfonate (CaLS) solution, then transfer it to the reactor. Adjust the pH of the mixture to 11 with 1M KOH solution, heat to 45°C, and continuously purge with nitrogen for 30 min. Add 100 g of... 2-Acrylamido-2-methylpropanesulfonic acid (AMPS) was dissolved in 200 mL of deionized water. A 50 wt% AMPS solution was added to the reactor. 1.6 g of ammonium persulfate (oxidant) and 1.6 g of ascorbic acid (reducing agent) were dissolved in 30 mL of deionized water, and divided into three equal portions. One portion of the ammonium persulfate solution was added dropwise to the reactor, followed by the addition of the ascorbic acid solution after 30 min. The reaction was allowed to proceed for 1.5 h. The remaining 50 wt% AMPS solution was then added to the system, followed by the addition of the ammonium persulfate solution, and then the addition of the ascorbic acid solution after 30 min. The reaction was allowed to proceed for 1.5 h to obtain a lignin polymer solution. 5 g of trimethylolpropane tris(3-mercaptopropionic acid) ester was dissolved in 70 mL of deionized water. A solution of trimethylolpropane tris(3-mercaptopropionic acid) was obtained by dissolving the trimethylolpropane tris(3-mercaptopropionic acid) in 95% ethanol solution. The trimethylolpropane tris(3-mercaptopropionic acid) solution was then slowly added dropwise to the above lignin copolymer system solution. The remaining ammonium persulfate solution was added dropwise, and the remaining ascorbic acid solution was added dropwise after 30 min. The experiment was ended after 2.5 h of reaction. The mixture after the above reaction was cooled to room temperature and dried in an oven at 60 °C to obtain lignin-based saline-alkali soil improvement material.

[0095] Example 4

[0096] I. Material Synthesis Mechanism

[0097] Figure 1 The synthesis process of CaLS-AMPS / DMC / TMPMP prepared in Example 1 is described. The synthesis mechanism of this material mainly consists of two core steps: anionic and cationic modification of lignin and click chemistry introduction of thiol monomers. First, the water-soluble initiator ammonium persulfate (APS) and ascorbic acid undergo a redox reaction to generate highly oxidizing sulfate anion free radicals (SO4•-). -The system first introduces cationic monomer DMC. Free radicals in the system preferentially attack the carbon-carbon double bonds on the DMC molecule, undergoing an addition reaction to generate DMC monomer free radicals. These DMC free radicals then copolymerize with phenolic radicals generated on the CaLS backbone due to free radical attack, branching DMC branches onto the lignin backbone through chain growth, increasing lignin solubility. Subsequently, anionic monomer AMPS is added. At this point, various free radicals in the system attack the carbon-carbon double bonds of AMPS, generating AMPS monomer free radicals or causing the polymer chain ends to become AMPS units. Finally, through a free radical copolymerization mechanism, DMC and AMPS are co-grafted onto the same lignin molecule, forming a zwitterionic copolymer (CLS-AMPS / DMC) carrying both positive and negative charges. Trimethylolpropane tris(3-mercaptopropionic acid) ester with terminal thiol groups (-SH) was added to the above zwitterionic polymer system. The DMC monomer and AMPS grafted on the polymer chain have unsaturated olefin bonds. Through the polarity regulation of the above materials, the thiol groups are encouraged to achieve confined and regular arrangement. These olefin bonds undergo a highly efficient "thiol-olefin" click chemical reaction with the thiol groups (-S) on the trimethylolpropane tris(3-mercaptopropionic acid) ester. Figure 2 Based on the principle of dynamic disulfide bond formation, the thiol group on poly(trimethylolpropane)tris(3-mercaptopropionic acid) ester can shield the surface charge of the material under high sodium ion concentration, reduce electrostatic repulsion, and allow the chain to approach and oxidize to generate dynamic disulfide bonds (-SS-). Figure 3 The material's responsiveness to pH and sodium ion stimulation was demonstrated. Under high pH conditions, the negatively charged sulfonic acid groups exhibit strong electrostatic attraction with the quaternary ammonium salt cationic groups in the molecular chain, causing the polymer chain to change from an extended conformation to a contracted and coiled state. This conformational change further promotes intermolecular bonding through hydrophobic interactions, enhancing the adsorption and encapsulation capacity of soil particles, thereby promoting the formation of stable soil micro-aggregates. Regarding sodium ion response, the thiol groups introduced into the material can undergo dynamic oxidation in high sodium ion concentration environments through electrostatic shielding, forming disulfide bonds, initiating polymer network aggregation and effectively immobilizing sodium ions.

[0098] II. Material Characterization

[0099] 1. Macroscopic physical state and scanning electron microscopy (SEM)

[0100] Figure 4 Macroscopic images and SEM images of the biomimetic lignin-based saline-alkali land improvement materials prepared in Examples 1-3 are shown. Figure 4 In (1), the macroscopic physical states of materials with different ratios can be observed. Example 1 is a high-viscosity aqueous solution, Example 2 is a low-viscosity aqueous solution, and Example 3 is a stretchable gel. To better observe the surface morphology of the materials, from Figure 4As can be seen from the scanning electron microscope image (2) in Example 1, the biomimetic lignin-based saline-alkali soil improvement material has a dense and continuous three-dimensional network with small and uniform pore size, thick walls, and many cross-linking points, exhibiting a compact structure that reflects high entanglement and high cohesion. Compared with Example 1, Example 2 has a looser structure, larger and unevenly distributed pore size, thin and smooth walls, and fewer cross-linking points; Example 3 forms a three-dimensional porous network structure, which is a typical gel morphology, with thicker pore walls and a coherent structure.

[0101] 2. Fourier transform infrared spectroscopy

[0102] Figure 5 The functional groups of CaLS, DMC, and CaLS-AMPS / DMC / TMPMP prepared in Example 1 were determined by Fourier transform infrared spectroscopy. Compared with the Fourier transform infrared spectrum of CaLS, the functional groups of CaLS-AMPS / DMC / TMPMP at 2570, 1726, 1640, 1480, and 950 cm⁻¹ were significantly different. -1 A new peak appeared at 2570cm. -1 The stretching vibration peak at 1726 cm⁻¹ corresponds to a thiol group (SH), indicating successful introduction of a surface polythiol monomer. -1 The stretching vibration peak at 1640 cm⁻¹ is due to the introduction of a carbonyl group (C=O) into DMC. -1 The characteristic absorption peak is that of the amide group, belonging to the amide I band, confirming the presence of the amide group; simultaneously, at 1038 cm⁻¹... -1 The enhanced characteristic absorption peaks indicate an increase in the content of sulfonic acid groups. The co-occurrence of these two key characteristic peaks strongly demonstrates that AMPS has been successfully introduced into the copolymer. (1480 and 950 cm⁻¹) -1 The characteristic absorption peak at that location corresponds to the bending vibration of the -CN group adjacent to the quaternary ammonium group in the DMC monomer and the -CH2-N group. + The stretching vibration of (CH3)3, the successful graft copolymerization of quaternary ammonium groups on the surface, the successful construction of zwitterionic polymers on the surface, and the successful introduction of thiol monomers.

[0103] 3. Cationicity, anionicity, and intrinsic viscosity

[0104] The cationicity was measured according to national standard GB / T 31246-2014, and the anionicity and intrinsic viscosity of the material were measured according to national standard GB / T 17514-2017. The results are shown in Table 1 below.

[0105]

[0106] As shown in Table 1, this invention, through stepwise and alternating copolymerization of quaternary ammonium salt monomers and sulfonic acid anionic monomers, ensures that cationic and anionic groups are regularly and efficiently incorporated into the lignin molecular chain, allowing them to be fully exposed and promoting the confinement and regular arrangement of thiol groups, thereby efficiently completing the thiol-alkene click chemistry reaction. In contrast, Comparative Example 1, due to the simultaneous addition of all monomers, resulted in a large amount of copolymerization caused by the competitive polymerization rate, leading to a decrease in grafting rate and molecular weight. Comparative Example 2, due to the simultaneous addition of the initiator, resulted in excessively high free radical concentrations causing random cross-linking between molecules. Both of these significantly reduced the effective ionicity and molecular weight of the material. Comparative Example 3 used itaconic acid instead of AMPS. Itaconic acid has poor water solubility and organic material solubility. Its molecular structure contains two carboxyl groups, and the spatial structure between the two carboxyl groups creates an obstacle. This obstacle becomes more pronounced during polymerization, making it difficult for the carboxyl groups to contact the remaining itaconic acid, resulting in low graft copolymerization efficiency, low anionicity, and low intrinsic viscosity. Comparative Example 4 was a pure cationic monomer polymerization, and Comparative Example 5 was a pure anionic polymer. Both disrupted the charge balance of the material design and lost the advantage of the synergistic effect of anions and cations. Due to the inability to control the polarity of lignin, the multi-thiol reaction efficiency was low.

[0107] III. Material Response Testing

[0108] 1. pH responsiveness test

[0109] To verify whether the lignin-based saline-alkali soil amendments prepared in Examples 1-2 undergo the expected chain conformational transformation under different pH conditions, their pH response behavior was quantitatively characterized by measuring the turbidity of their aqueous solutions. The specific method is as follows: The lignin-based saline-alkali soil amendment was prepared into a 0.01 g / mL solution. Then, the pH value of each sample tube was precisely adjusted using 0.1 M HCl or KOH solution to form a pH gradient. The pH of the solution was adjusted to approximately 4, 6, 8, 10, and 12 to construct experimental gradients under different pH conditions. The changes in the macroscopic morphology of the solution with pH are shown below. Figure 6 As shown. By Figure 6 It can be seen that flocculent precipitates begin to appear in the solutions of lignin-based saline-alkali soil amendments at a pH of around 8. As the pH value further increases, the flocculent matter gradually increases in quantity and size, eventually forming a three-dimensional network gel structure. This phenomenon indicates that the lignin-based saline-alkali soil amendments prepared in Examples 1-2 exhibit significant response characteristics under different acid-base and ionic strength environments.

[0110] 2. Sodium ion response test

[0111] Take 0.5g of the lignin-based saline-alkali soil improvement material prepared in Examples 1-2 and dissolve it in 10mL of deionized water. Add 5mL of NaCl solution with a concentration of 10g / L and observe the sodium ion response behavior.

[0112] Response behavior such as Figure 7 As shown, when NaCl is added to a lignin-based saline-alkali soil material solution, flocculent precipitate can be observed forming in the solution. This is because with the addition of NaCl, Na... + Neutralization and charge repulsion cause a sharp increase in the concentration of sodium ions in the solution, resulting in a high concentration of Na+. + It enters the three-dimensional network structure of the material, making it easier for the material to approach and promoting the formation of disulfide bonds.

[0113] IV. Effects of Saline-Alkali Land Improvement

[0114] 1. Flocculation behavior of severely saline-alkali soil

[0115] To verify the effect of the prepared saline-alkali land amendment material on soil aggregates, we designed a small-tube flocculation and sedimentation experiment. Lower turbidity and faster sedimentation of surface soil particles indicate better soil aggregate flocculation and stronger amendment material performance. Nine treatments were set up: CK (no soil amendment material), Examples 1-3 (addition of 0.1 wt% saline-alkali soil), and Comparative Examples 1-5 (addition of lignin-based saline-alkali land amendment material). 5 g of saline-alkali soil (topsoil (0-15 cm) from Kenli County, Dongying City, Shandong Province (37°70'N, 118°85'E), sieved to 2 mm, air-dried, pH 8.6, EC 9.6 ms / cm, sodium ion content 5.32 mg / g) was added to a 50 mL test tube. Then, 45 mL of deionized water was added, the mixture was vigorously shaken for 90 s, and allowed to stand. The turbidity of the soil supernatant was measured after 5 min. Figure 8 As shown.

[0116] like Figure 8 As shown, the mean turbidity of the supernatant in the control group (CK) was 264.67 NTU, indicating that without the addition of amendments, saline-alkali soil has strong dispersibility in water, making it difficult for soil aggregates to form, resulting in high turbidity of the supernatant. In contrast, the mean turbidity of the supernatant in Examples 1-3 was significantly lower than that in the CK group, with Example 1 showing the best effect, reducing turbidity by 91.96% compared to CK.

[0117] Compared to Comparative Examples 1 and 2, Example 1 employed a distributed activation and alternating copolymerization process, avoiding the chain segment mixing problem that occurred when AMPS and DMC were fed simultaneously due to large differences in their polymerization rates. This resulted in a more uniform alternating copolymerization structure. This structure allows the material to simultaneously adsorb negatively charged clay particles and positively charged iron oxide and humus on the same molecular chain, forming a synergistic effect of both "patch-charge neutralization" and "bridging" mechanisms, effectively solving the problem of highly dispersed particles in saline-alkali soils.

[0118] The difference between Comparative Example 3 and Examples 1-3 is that itaconic acid was used instead of 2-acrylamido-2-methylpropanesulfonic acid (AMPS). The turbidity of its supernatant decreased by only 39.55% compared to the control (CK), which is far lower than the effect of Examples 1-3. This indicates that itaconic acid has a lower polymerization efficiency due to its large steric hindrance, and the effect of the subsequently introduced thiol group is not ideal. At the same time, the hydration radius of the carboxylic acid group is smaller than that of the sulfonic acid group, which affects the flocculation performance of the aggregates.

[0119] Comparative Examples 4 and 5 introduced only anionic or cationic monomers, respectively. Since the synergistic effect of positive and negative charges could not be achieved, the soil flocculation effect was significantly reduced.

[0120] 2. Experiment on structural improvement of severely saline-alkali soil

[0121] This experiment used PVC pipes with a diameter of 5 cm, a height of 20 cm, and a perforated bottom to conduct soil column leaching experiments to verify the improvement effect of the material on soil permeability and sodium ion removal rate. Two layers of gauze were placed at the bottom of each column, and a layer of quartz sand approximately 1 cm thick was laid to prevent soil seepage. A 200 mL beaker was placed below the soil column to collect the leachate. Five treatments were set up: a control group (CK), and treatments with 0.01% (by soil mass) of the lignin-based saline-alkali soil amendment materials prepared in Examples 1, 2, Comparative Examples 1, and 3. Each treatment was repeated three times. Air-dried soil (topsoil (0-15 cm) taken from Kenli County, Dongying City, Shandong Province (37°70'N, 118°85'E), sieved to 2 mm, air-dried, pH 8.81, EC 9.6 ms / cm, and sodium ion content 5.32 mg / g) was passed through a 2 mm sieve and thoroughly mixed with the saline-alkali soil amendment material. A 300g mixed soil sample was placed into a soil column in three portions, each time compacted naturally. The soil was initially irrigated with 90mL of deionized water, and the soil column was left at room temperature for two days to allow the saline-alkali soil amendment material to fully react with the soil. Then, a leaching experiment was conducted using deionized water. Another 90mL of water was added at once, and the time it took for water to flow out from the bottom of the soil column was observed and recorded. The volume of the leachate was measured directly using a graduated cylinder. Leaching was considered complete when no liquid flowed out from the bottom of the soil column within 30 minutes. The total infiltration time was recorded. After leaching, the soil was drained and air-dried, and the soil electrical conductivity (EC) and Na+ content were measured. + concentration.

[0122] Examples 1, 2, Comparative Example 1, and Comparative Example 3 show the following differences in infiltration time and leachate volume: Figure 9As shown in the figure. Compared with the control group (CK), Examples 1 and 2 significantly shortened the soil infiltration time by 39.32% and increased the leachate volume by 3%-8%. This is because the addition of the amendment material improved the soil aggregate structure and increased soil porosity, thereby improving water infiltration efficiency. However, the amendment effects of Comparative Examples 1 and 3 were relatively weak, with no significant reduction in infiltration time or change in leachate volume, indicating that their ability to improve soil permeability and soil structure is limited.

[0123] Table 2 shows the soil EC values ​​and sodium ion content. As can be seen from Table 2, the soil EC values ​​after treatments in Examples 1-2 were significantly reduced, decreasing by 66.11% and 54.27% respectively. The water-soluble Na in the soil... + The concentration decreased by 56%-67.69%, indicating that Examples 1-2 had a significant effect on the removal of sodium ions from saline-alkali soil. In contrast, the EC values ​​of Comparative Example 1 and Comparative Example 3 decreased by 16.92% and 24.42%, respectively. + The concentrations decreased by 32.63% and 18.18%, respectively, indicating a significantly lower improvement effect compared to the example.

[0124]

[0125] 3. Corn pot experiment

[0126] A pot experiment using maize was conducted to verify the effectiveness of the lignin-based soil amendment. Soil samples (0-15 cm) were taken from Kenli County, Dongying City, Shandong Province, sieved to 2 mm, air-dried, with a pH of 8.7 and an EC value of 3.11 ms / cm. Five treatments were set up: a control group (CK), and treatments supplemented with 0.01% (by soil mass) of the lignin-based saline-alkali soil amendment prepared in Examples 1, 2, 1, and 3. Each treatment was repeated three times.

[0127] The lignin-based saline-alkali soil amendment was thoroughly mixed with 1.2 kg of soil. Filter paper was placed at the bottom of the pot, and 1 kg of the soil mixture was added into the pot. Before planting, 480 mL of deionized water was added to each pot to balance the soil. Two days later, three corn seeds (variety "Zhengdan 958", Hebei Maohua Seed Industry Co., Ltd.) were planted in each pot, and the remaining 200 g of mixed soil sample was placed on top of the seeds. After seven days of growth, thinning was carried out, leaving one seedling with relatively uniform growth in each pot. After seed emergence, 100 mL of water was added every three days, and no fertilizer was applied during the entire growth period. After 30 days of cultivation, the seedlings were harvested and relevant indicators were measured. Table 3 shows the effect of the lignin-based saline-alkali soil amendment on the dry weight, fresh weight, and plant height of corn seedlings, and Table 4 shows the effect of the lignin-based saline-alkali soil amendment on the proportion of soil microaggregates.

[0128] As shown in Table 3, the fresh weight, dry weight and plant height of corn in Example 1 were significantly increased compared with those in CK, by 39.19%, 41.52% and 31.36% respectively. This result indicates that the lignin-based conditioner can promote the growth of corn seedlings, reduce soil salinity and create a more suitable environment for corn root elongation.

[0129]

[0130] Further analysis of the soil water-stable aggregate composition was conducted using the wet sieving method, and the results are shown in Table 4. Table 4 shows that, compared to the control (CK), the proportion of aggregates with a particle size greater than 0.25 mm in Examples 1 and 2 significantly increased by 47.91% and 37.3%, respectively. This indicates that the dual-response lignin-based saline-alkali soil amendment material can enhance aggregate stability, effectively improve soil structure, and optimize the soil physical environment.

[0131]

[0132] Figure 10 The effects of lignin-based saline-alkali soil amendments on the properties of potted soil, such as Figure 10 As shown, compared with the control (CK), the soil pH, EC value, and sodium ion concentration in Examples 1 and 2 all decreased. Specifically, the soil pH decreased from 8.44 in the CK to 8.19 and 8.10, respectively; the EC value decreased significantly by 58.81% and 43.29%, respectively; and the sodium ion concentration decreased... + The concentrations also decreased to 43.52% and 33.21%, respectively. This result indicates that lignin-based saline-alkali soil amendments can reduce soil pH, decrease salt accumulation, and reduce Na+. + The enrichment level effectively alleviates the growth inhibition of maize seedlings by salt and alkali stress, thereby promoting the growth of maize seedlings.

[0133] 4. Germination experiment of saline-treated seeds

[0134] A 25 mmol / L NaCl solution was used to simulate salt stress. Three treatments were set up: control (CK), 0.5 wt% of the lignin-based saline-alkali soil amendments from Examples 1 and 2, and a mixed solution was obtained. In the germination experiment, cucumber seeds were disinfected with sodium hypochlorite for 10 min. Ten seeds were placed in a petri dish containing filter paper, and 10 mL of the above mixed solution was transferred onto the filter paper. Four days later, the germination rate (GR) and average shoot length (ABL) of the seeds were measured, and the results are shown in Table 5. As can be seen from Table 5, under simulated salt stress conditions, 0.5 wt% lignin soil amendment significantly improved the germination rate and shoot length of cucumber seeds, effectively alleviating the inhibitory effect of salt on seed germination, and showing a good salt stress relief effect.

[0135] .

Claims

1. A method for preparing a lignin-based saline-alkali land improvement material, characterized in that: The preparation method includes the following steps: Lignin and / or lignin derivatives were modified by aqueous solution polymerization with sulfonic acid anionic monomers and quaternary ammonium salt cationic monomers to obtain an amphiphilic anionic-cationic lignin composite system solution. Then, multi-thiol monomers were introduced by click chemistry to prepare lignin-based saline-alkali soil improvement materials. The preparation method specifically includes the following steps: S1. Adjust the pH of the lignin and / or lignin derivative solution and heat it; divide the quaternary ammonium salt cationic monomer solution into two equal parts by volume, and add one part to the lignin and / or lignin derivative solution; divide the oxidant and reducing agent solutions into three equal parts by weight, add one part of the oxidant solution to the above solution, and then add one part of the reducing agent solution, and react. S2. Divide the sulfonic acid anion monomer solution into two equal parts by volume. Add one part of the sulfonic acid anion monomer solution to the system obtained in S1 and react. Then add the other part of the quaternary ammonium salt cationic monomer solution, add one part of the oxidant solution, add one part of the reducing agent solution, and finally add the other part of the sulfonic acid anion monomer solution and react. The resulting anion-cationic lignin composite system solution is obtained. S3. Mix the multi-thiol monomer solution and the anion-cationic lignin composite system solution, add one part of oxidant solution and then one part of reducing agent solution, react, and after drying, obtain the lignin-based saline-alkali land improvement material. The lignin derivative is at least one of calcium lignin sulfonate, sodium lignin sulfonate, magnesium lignin sulfonate, potassium lignin sulfonate, ammonium lignin sulfonate, alkali lignin, sulfate lignin, groundwood lignin, alkylated lignin, aminoated lignin, hydroxymethylated lignin, acetylated lignin, and oxidized lignin. The sulfonic acid anionic monomer is at least one of 2-acrylamido-2-methylpropanesulfonic acid, acrylamide tert-butylsulfonic acid, 2-(methacryloyloxy)ethyldimethyl-(3-sulfopropyl)ammonium hydroxide, sulfopropyl methacrylate, sodium methpropylene sulfonate, sodium propylene sulfonate, sodium 3-allyloxy-2-hydroxypropanesulfonate, potassium 3-sulfopropyl acrylate, potassium sulfopropyl methacrylate, sodium vinyl sulfonate, and sodium p-styrene sulfonate. The quaternary ammonium salt cationic monomer is at least one selected from methacryloyloxyethyltrimethylammonium chloride, dimethyl diallyl ammonium chloride, acryloyloxyethyltrimethylammonium chloride, methacrylamidopropyltrimethylammonium chloride, benzylvinyltrimethylammonium chloride, methacryloyloxyethyldimethylbenzylammonium chloride, 2-acrylamidoethyldimethyldodecylammonium bromide, and allyltrimethylammonium chloride. The polythiol monomer is at least one of trimethylolpropane tris(3-mercaptopropionic acid), pentaerythritol tetrakis(3-mercaptopropionic acid), ethylene glycol di(3-mercaptopropionic acid), trimethylolpropane tris(2-mercaptoacetate), pentaerythritol tetramercaptoacetate, and hexa(3-mercaptopropionic acid) dipentaerythritol ester. The ratio of the total mass of the sulfonic acid anionic monomer and the quaternary ammonium salt cationic monomer to the mass of the lignin and / or lignin derivative is 2-16:1; The mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is 1:8 to 8:1; The mass ratio of lignin and / or lignin derivatives to polythiol monomers is 5-15:

1.

2. The preparation method according to claim 1, characterized in that: The mass percentage concentration of the lignin and / or lignin derivative is 5%-35%; The quaternary ammonium salt cationic monomer solution has a mass percentage concentration of 60%-80%; the solvent for the quaternary ammonium salt cationic monomer solution is water. The oxidant is at least one of ammonium persulfate, potassium persulfate, sodium persulfate, and hydrogen peroxide; The reducing agent is at least one of ascorbic acid, sodium bisulfite, sodium sulfite, and sodium thiosulfate; The mass percentage concentration of the oxidant and reducing agent solution is 3%-15%; The sulfonic acid anion monomer solution has a mass percentage concentration of 30%-65%; the solvent for the sulfonic acid anion monomer solution is water. The mass percentage concentration of the polythiol monomer solution is 3.5%-30%; the solvent of the polythiol monomer solution is an ethanol solution. The total mass of the oxidizing agent and reducing agent is 0.5%-5% of the total mass of the lignin and / or lignin derivatives, quaternary ammonium cationic monomers, sulfonic acid anionic monomers and polythiol monomers; The mass ratio of the oxidant to the reducing agent is 1:1-1.

5.

3. The preparation method according to claim 2, characterized in that: When the mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is in different ranges, the lignin-based saline-alkali soil improvement material exhibits drastically different macroscopic physical states: When the mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is 1:1.5 to 1.5:1, the lignin-based saline-alkali soil improvement material forms a stretchable gel state. When the mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is between 1:1.5 and 1:8, and does not include 1:1.5, the lignin-based saline-alkali soil improvement material forms a high-viscosity aqueous solution. When the mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is between 1.5:1 and 8:1, but does not include 1.5:1, the lignin-based saline-alkali soil amendment material forms a low-viscosity aqueous solution.

4. The preparation method according to claim 1, characterized in that: In step S1, the pH of the lignin and / or lignin derivative solution is adjusted to 10-12 using KOH solution; The heating temperature is 35-50℃; The reaction time is 1-2 hours; In step S2, a portion of sulfonic acid anionic monomer solution is added to the system obtained in S1, and the reaction time is 1-2 hours. After adding another portion of the sulfonic acid anion monomer solution, the reaction time is 1-2 hours. In step S3, the reaction time is 2-4 hours.

5. The preparation method according to claim 1, characterized in that: In steps S1, S2 and S3, the oxidizing agent solution is added dropwise for 30 minutes, followed by the addition of the reducing agent solution. In step S3, the multi-thiol monomer solution is added dropwise to the anion-cation lignin composite system solution at a flow rate of 0.5-15 mL / min.

6. The lignin-based saline-alkali land improvement material prepared by the preparation method according to any one of claims 1-5.

7. The application of the lignin-based saline-alkali soil amendment material according to claim 6 in the improvement of saline-alkali soil.

8. The application according to claim 7, characterized in that: Based on the different mass ratios of the sulfonic acid anionic monomer and the quaternary ammonium salt cationic monomer, and the lignin-based saline-alkali soil improvement material obtained after reaction with polythiol monomers, the following application methods and dosages are adopted: 1) When the mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is 1:1.5 to 1.5:1, it can be applied directly to the soil as a soil conditioner or used as a coating material; wherein, the application rate of the soil conditioner is 40-200 kg / mu, and the application rate of the coating material is 3%-20% of the total mass of the coating fertilizer; 2) When the mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is between 1:8 and 1:1.5 and does not include 1:1.5, the resulting material is prepared as an aqueous solution for foliar spraying or drip irrigation; for foliar spraying, the concentration is prepared at 0.5%-2% and the dosage is 20-50 kg / mu; for drip irrigation, the concentration is prepared at 0.01-2% and the dosage is 20-150 kg / mu. 3) When the mass ratio of the sulfonic acid anionic monomer to the quaternary ammonium salt cationic monomer is between 1.5:1 and 3:1 and does not include 1.5:1, the resulting material is used as a root-dipping agent for seedlings. When using it, dilute it to a mass concentration of 0.1% to 0.3%, soak the crop roots in the solution for 5 minutes, and then plant it.

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