A modified lignin-based slow-release pesticide formulation and a preparation method thereof

Abstract

This invention discloses a modified lignin-based slow-release pesticide formulation and its preparation method, belonging to the field of pesticide formulation technology. First, sulfonated lignin is prepared through hydrogen peroxide-free radical graft copolymerization. Then, it is reacted with chitosan via a complex coagulation reaction to prepare chlorfenapyr microcapsules. Simultaneously, modified biochar is impregnated with sodium carboxymethyl cellulose. Finally, the chlorfenapyr microcapsules are compounded with modified biochar, dispersants, wetting agents, antifreeze stabilizers, and other adjuvants to obtain the modified lignin-based slow-release pesticide formulation. This invention, through the encapsulation of pesticides in sulfonated lignin / chitosan microcapsules and the synergistic loading effect of modified biochar, achieves synergistic optimization of the pesticide formulation's suspension stability, storage stability, long-lasting slow-release effect, and salt-alkali tolerance. It effectively solves the problems of traditional pesticides being prone to failure and having a short duration of effect under saline-alkali conditions, making it suitable for long-term control of crop diseases and pests in saline-alkali land.

Description

Technical Field

[0001] This invention belongs to the field of pesticide formulation technology, specifically a modified lignin-based slow-release pesticide formulation and its preparation method. Background Technology

[0002] Slow-release pesticide formulations are a key technology for achieving reduced pesticide dosage, increased efficacy, extended duration of action, and reduced environmental pollution. Their core lies in regulating the release rate of active pesticide ingredients through carrier materials, reducing pesticide leaching, volatilization, and photodegradation losses in the field, thereby improving pesticide utilization and application safety. This is an important direction for the development of green agriculture.

[0003] Lignin, a major byproduct of the pulp and paper industry, boasts advantages such as wide availability, renewability, good biocompatibility, and low cost. Its molecular structure contains active groups such as phenolic and alcoholic hydroxyl groups, providing a structural basis for pesticide loading and sustained release, making it a highly promising green sustained-release carrier material. However, natural lignin suffers from drawbacks such as strong structural heterogeneity, poor pesticide compatibility, and insufficient sustained-release performance, limiting its application in sustained-release pesticide formulations.

[0004] Chinese patent application CN119325980A discloses a sustained-release compound formulation based on difenoconazole and its preparation method. This scheme introduces ester functional monomer molecules into the basic structure of lignin to construct a modified lignin coating solvent, thereby achieving the encapsulation and sustained release of difenoconazole. At the same time, by utilizing the antioxidant and photodegradation resistance properties of lignin, the stability and duration of action of the pesticide formulation are improved to a certain extent, providing a feasible path for the development of lignin-based sustained-release pesticides.

[0005] However, the ester-modified lignin carrier of this scheme has significant technical limitations in high pH environments: the pH of saline-alkali soils in my country is generally above 8.5, and the ester-modified groups introduced in the scheme are prone to rapid hydrolysis in high pH environments, leading to premature rupture of the lignin coating, explosive release of pesticide active ingredients, and a significant shortening of the controlled-release period, making it impossible to maintain a long-term stable controlled-release effect. At the same time, the high salt ion environment in saline-alkali soils will exacerbate the structural instability and aggregation of the carrier, further damaging the controlled-release performance of the formulation, making it difficult to meet the core requirements of long-term controlled-release and stable control efficacy of pesticide formulations in saline-alkali soil scenarios. Summary of the Invention

[0006] The purpose of this invention is to provide a modified lignin-based slow-release pesticide formulation and its preparation method. By encapsulating the pesticide in sulfonated lignin / chitosan microcapsules and synergistically using modified biochar for loading, the pesticide formulation achieves synergistic optimization of suspension stability, storage stability, slow-release long-term effect, and salt and alkali resistance. This effectively solves the problem of traditional pesticides being prone to failure under saline and alkali conditions and is suitable for long-term control of crop diseases and pests in saline and alkali land.

[0007] The objective of this invention can be achieved through the following technical solutions: This invention provides a modified lignin-based slow-release pesticide formulation, which is prepared by mixing modified biochar, sodium lignin sulfonate, sodium dodecylbenzene sulfonate, ethylene glycol, xanthan gum, deionized water and chlorfenapyr microcapsule powder.

[0008] This invention also provides a method for preparing a modified lignin-based slow-release pesticide formulation, comprising the following steps: Step 1: Using lignin as raw material, it is first activated by hydrogen peroxide, and then subjected to free radical graft copolymerization with sodium allyl sulfonate under the action of an initiator to obtain sulfonated lignin.

[0009] Furthermore, the specific preparation steps of sulfonated lignin are as follows: Lignin, dioxane, and deionized water were added to a reaction vessel and stirred at 55-65℃ and 250-350 r / min until dissolved. The pH of the solution was slowly adjusted to 3.5-4.5 with dilute hydrochloric acid. Hydrogen peroxide with a mass fraction of 30% was slowly added to the vessel, and the reaction was maintained at the same temperature for 0.8-1.2 h. The temperature was then raised to 80-90℃, and sodium allyl sulfonate aqueous solution with a concentration of 1 mol / L was added dropwise at a uniform rate over 1.5 h through a constant pressure dropping funnel. A mixed solution of potassium persulfate and sodium bisulfite was added dropwise simultaneously over 1 h. After the addition was completed, the reaction was maintained at the same temperature for another 0.8-1.2 h. After the reaction was completed, the mixture was cooled to room temperature, and the pH of the system was adjusted to 8-9 with dilute sodium hydroxide. The mixture was filtered to remove impurities, and the filtrate was concentrated under reduced pressure to 1 / 3 of its original volume. The concentrate was then slowly poured into 5 times its volume of anhydrous ethanol, allowed to stand for 2-4 h, filtered to collect the precipitate, washed, and dried to obtain sulfonated lignin.

[0010] The ratio of lignin, dioxane, deionized water, 30% hydrogen peroxide, 1 mol / L sodium allyl sulfonate aqueous solution, and potassium persulfate-sodium bisulfite mixed solution is 6-9 g: 60-90 mL: 60-90 mL: 6-9 g: 60-90 mL: 40-50 mL.

[0011] The potassium persulfate-sodium bisulfite mixed solution is prepared by mixing potassium persulfate, sodium bisulfite and deionized water in a ratio of 1-1.5g:0.4-0.5g:40-50mL.

[0012] Step 2: Using sulfonated lignin and chitosan as wall materials and chlorfenapyr as the core, chlorfenapyr microcapsule powder is obtained through emulsification dispersion, electrostatic re-coagulation and glutaraldehyde cross-linking and curing.

[0013] Furthermore, the specific preparation steps of the chlorfenapyr microcapsule powder are as follows: Chitosan and a 1% (w / w) aqueous acetic acid solution were added to a reaction vessel and stirred at 35-45℃ and 250-350 rpm until dissolved. The pH was adjusted to 4.5-5 with dilute sodium hydroxide solution, and stirring was continued. The chlorfenapyr oil phase solution and emulsifier Tween-80 were slowly added to the vessel in sequence. After the addition was complete, emulsification was carried out at 700-900 rpm for 20-30 min. Then, sulfonated lignin solution was added dropwise to the vessel within 15-20 min. The reaction was stirred at 35-45℃ and 250-350 rpm for 10-20 min. A 25% (w / w) glutaraldehyde solution was added to the vessel, and the pH of the system was adjusted to 6-6.5 with dilute sodium hydroxide solution. The reaction was stirred at the same temperature and speed for 1.5-2 h. After cooling to room temperature, the precipitate was collected by centrifugation, washed, and dried to obtain chlorfenapyr microcapsule powder.

[0014] The ratio of chitosan, 1% acetic acid aqueous solution, chlorfenapyr oil phase solution, emulsifier Tween-80, sulfonated lignin solution and 25% glutaraldehyde solution is 6-10g: 1.2-2L: 150-170mL: 3-5g: 600-1000mL: 14-23mL.

[0015] The sulfonated lignin solution is prepared by mixing sulfonated lignin and deionized water in a ratio of 12-20g:600-1000mL.

[0016] The chlorfenapyr oil phase solution is prepared by mixing chlorfenapyr technical and solvent oil S-150 at a ratio of 6-10g:150-170mL.

[0017] Step 3: Mix and disperse the modified biochar with chlorfenapyr microcapsule powder, sodium lignosulfonate, sodium dodecylbenzenesulfonate, ethylene glycol, xanthan gum and deionized water to prepare a modified lignin-based slow-release pesticide formulation.

[0018] The ratio of modified biochar, sodium lignosulfonate, sodium dodecylbenzenesulfonate, ethylene glycol, xanthan gum, deionized water, and chlorfenapyr microcapsule powder is 8-12g: 1.5-2.5g: 0.8-1.2g: 4-6g: 0.4-0.6g: 40-60mL: 25-35g.

[0019] Furthermore, the specific preparation steps of modified biochar are as follows: Sodium carboxymethyl cellulose and deionized water were added to a reactor and stirred at 55-65℃ and 250-350 r / min until dissolved. Pretreated biochar was added to the reactor and stirred for 6 h to allow CMC molecules to diffuse and adsorb fully. Then, the mixture was allowed to stand for 0.8-1.2 h to allow unloaded CMC molecules to settle and age fully. The mixture was then filtered, washed, and dried to obtain modified biochar.

[0020] The ratio of sodium carboxymethyl cellulose, deionized water, and pretreated biochar is 2.5-3.4g: 180-220mL: 35-45g.

[0021] Pretreated biochar was prepared by passing 40-60g of corn stalk biochar through a 60-mesh sieve to remove impurities and drying it at 105℃ for 20-28h.

[0022] The beneficial effects of this invention are: 1. This invention effectively improves the shortcomings of traditional pesticide formulations, such as easy flocculation and failure and short duration of effect under saline-alkali conditions, through the synergistic effect of sulfonated lignin / chitosan microcapsule encapsulation and modified biochar loading. It achieves simultaneous improvement in suspension stability, storage stability and slow-release long-term effect in saline-alkali environment, which can meet the actual needs of long-term prevention and control of crop diseases and pests in saline-alkali land.

[0023] 2. The chlorfenapyr microcapsule powder prepared by this invention has multiple advantages: First, the sulfonic acid groups and amino groups contained in its capsule wall can form a dense electrostatic cross-linking structure, giving the microcapsules excellent alkali resistance and stability, making them less prone to swelling and rupture in high saline-alkali environments, and able to stably encapsulate the active ingredients; Second, the microcapsule encapsulation structure can act as a physical barrier to protect chlorfenapyr, reducing its rapid degradation and loss due to light and moisture during application, while achieving slow and controllable release, significantly prolonging the duration of efficacy; Third, the hydrophilic groups on the surface of the capsule wall can form good compatibility with water-based systems, improving the dispersibility of the microcapsules, and can also synergistically work with the polar groups on the surface of modified biochar to further enhance the suspension stability of the formulation.

[0024] 3. The modified biochar of the present invention, on the one hand, after being modified by impregnation with sodium carboxymethyl cellulose, has a surface rich in polar groups, which can form a good interfacial bond with chlorfenapyr microcapsules, effectively dispersing and fixing the microcapsules and reducing the sedimentation and stratification of the formulation during storage; on the other hand, its porous structure can provide support for the microcapsules, reducing the possibility of mutual compression and aggregation of microcapsules during long-term storage, and can also synergize with excipients to further improve the suspension and cold and hot storage stability of the formulation; in addition, the modified biochar can also regulate the release behavior of microcapsules through adsorption, helping to prolong the drug release cycle and improving the long-term stability of the formulation. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1: A modified lignin-based slow-release pesticide formulation, prepared by the following steps: S1: Weigh 1.2g of potassium persulfate and 0.45g of sodium bisulfite and dissolve them in 45mL of deionized water. Stir until dissolved to obtain a potassium persulfate-sodium bisulfite mixed solution. Add 7.5g of lignin, 75mL of dioxane, and 75mL of deionized water to the reaction vessel. Stir for 1 hour at 60℃ and 300r / min until dissolved. Slowly adjust the pH of the solution to 4 with dilute hydrochloric acid. Slowly add 7.5g of 30% hydrogen peroxide to the vessel. Keep the reaction at the same temperature for 1 hour. Raise the temperature to 85℃ and pass the solution through a constant pressure dropping funnel. 75 mL of 1 mol / L sodium allyl sulfonate aqueous solution was added dropwise at a uniform rate over 1.5 hours, and 45 mL of potassium persulfate-sodium bisulfite mixed solution was added dropwise simultaneously over 1 hour. After the addition was complete, the reaction was continued at the temperature for 1 hour. After the reaction was completed, the mixture was cooled to room temperature, and the pH of the system was adjusted to 8 with dilute sodium hydroxide. Insoluble impurities were removed by filtration. The filtrate was concentrated to 1 / 3 of its original volume under reduced pressure, and the concentrate was slowly poured into 5 times its volume of anhydrous ethanol. The mixture was allowed to stand for 3 hours, and the solid precipitate was collected by filtration. The precipitate was washed three times with 80% ethanol and dried under vacuum at 40°C to constant weight to obtain sulfonated lignin.

[0027] A two-step method of hydrogen peroxide-hydroxylation and free radical graft copolymerization was adopted, using lignin as the natural polymer backbone. In a dioxane / water mixed solvent, the phenolic hydroxyl groups in the lignin molecule were first selectively oxidized to quinone structures by hydrogen peroxide under weakly acidic conditions, increasing the reactivity of the lignin molecule and improving its hydrophilicity. Subsequently, under the action of a potassium persulfate-sodium bisulfite redox initiation system, free radical active centers were generated, causing the sodium allyl sulfonate monomer to undergo a free radical graft copolymerization reaction with the lignin backbone. This introduced polymer side chains containing sulfonic acid groups onto the lignin backbone, achieving sulfonation modification of lignin and obtaining sulfonated lignin.

[0028] S2: Add 16g of sulfonated lignin to 800mL of deionized water, stir at 40℃ and 300r / min, slowly add a small amount of dilute sodium hydroxide solution to adjust the pH to 9, and continue stirring until completely dissolved to obtain a sulfonated lignin solution; add 8g of chlorfenapyr technical to 160mL of solvent oil S-150, stir magnetically at 45℃ until dissolved, and cool to room temperature to obtain a chlorfenapyr oil phase solution.

[0029] Add 8g of chitosan and 1.6L of 1% acetic acid aqueous solution to the reactor. Stir until completely dissolved at 40℃ and 300 rpm. Adjust the pH to 5 with dilute sodium hydroxide solution and continue stirring. Slowly add 160mL of chlorfenapyr oil phase solution and 4g of emulsifier Tween-80 to the reactor sequentially. After the addition is complete, emulsify for 25 minutes at 800 rpm. Then, add 800mL of [amount missing] dropwise to the reactor over 20 minutes. The sulfonated lignin solution was stirred for 15 min at 40℃ and 300 r / min. 18 mL of 25% glutaraldehyde solution was added to the reaction vessel, and the pH of the system was adjusted to 6 with dilute sodium hydroxide solution. The reaction was stirred for 1.5 h at the same temperature and speed. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was collected by centrifugation. The precipitate was washed 5 times with deionized water and acetone / ethanol mixed solution, and then dried under vacuum at 40℃ to constant weight to obtain chlorfenapyr microcapsule powder.

[0030] Using a complex coagulation-crosslinking method, with chlorfenapyr as the core, a composite capsule wall is generated in situ at the interface of an oil-in-water emulsion formed by electrostatic interaction between the amino groups of chitosan and the sulfonate groups of sulfonated wood (wall material). The capsule wall is then crosslinked and cured with glutaraldehyde to obtain chlorfenapyr microcapsules with a uniform particle size distribution (1-10 μm). The sustained-release mechanism of the microcapsules is mainly diffusion-controlled release, that is, the crosslinked composite capsule wall forms a semi-permeable membrane structure, and the active ingredient molecules are slowly released through the micropores of the wall material by diffusion. The release rate is regulated by the crosslinking density of the wall material, the micropore size, and the external osmotic pressure.

[0031] S3: 50g of corn stalk biochar was passed through a 60-mesh sieve to remove impurities and dried in an oven at 105℃ for 24h to obtain pretreated biochar. 3g of sodium carboxymethyl cellulose (CMC) and 200mL of deionized water were added to a reaction vessel and stirred at 60℃ and 300r / min until completely dissolved. 40g of pretreated biochar was added to the vessel and stirred at the same temperature and speed for 6h to allow CMC molecules to fully diffuse and adsorb onto the outer surface and mesopores of the biochar. The mixture was then allowed to stand for 1h to allow unloaded CMC molecules to fully settle and age. The residue was collected by filtration and washed with deionized water until the final filtrate was neutral. The residue was then dried at 75℃ to constant weight to obtain modified biochar.

[0032] Using an impregnation adsorption method with biochar as a carrier, the polar molecules of sodium carboxymethyl cellulose (CMC) undergo physical adsorption with the outer surface and mesopores (2-50 nm) of biochar, and are then stabilized by aging. This yields modified biochar with a surface rich in carboxyl and hydroxyl groups. The corn straw biochar used was prepared by pyrolysis at 600℃ and has abundant mesoporous and macroporous structures, providing sufficient adsorption sites for CMC molecules.

[0033] S4: 10g of modified biochar, 2g of sodium lignosulfonate as a dispersant, 1g of sodium dodecylbenzenesulfonate as a wetting agent, 5g of ethylene glycol as an antifreeze stabilizer, 0.5g of xanthan gum as a thickener, and 50mL of deionized water were added to a reaction vessel. The mixture was subjected to high-speed shearing at 800r / min for 20min. Then, 30g of chlorfenapyr microcapsule powder was slowly added to the vessel at 40℃ and 200r / min. The mixture was stirred at a constant temperature for 30min to ensure uniform dispersion of the components. After standing for 1.5h to defoam, the modified lignin-based slow-release pesticide formulation was obtained.

[0034] Example 2: A modified lignin-based slow-release pesticide formulation, prepared by the following steps: S1: Weigh 1g of potassium persulfate and 0.4g of sodium bisulfite and dissolve them in 40mL of deionized water. Stir until dissolved to obtain a potassium persulfate-sodium bisulfite mixed solution. Add 6g of lignin, 60mL of dioxane, and 60mL of deionized water to the reaction vessel. Stir for 1h at 55℃ and 250r / min until dissolved. Slowly adjust the pH of the solution to 3.5 with dilute hydrochloric acid. Slowly add 6g of 30% hydrogen peroxide to the vessel. Keep the reaction at the same temperature for 0.8h. Raise the temperature to 80℃ and drop the solution through a constant pressure funnel. 60 mL of 1 mol / L sodium allyl sulfonate solution was added dropwise at a uniform rate over 0.5 h, and 40 mL of potassium persulfate-sodium bisulfite mixed solution was added dropwise simultaneously over 1 h. After the addition was complete, the reaction was kept at the same temperature for 0.8 h. After the reaction was completed, the mixture was cooled to room temperature, and the pH of the system was adjusted to 8 with dilute sodium hydroxide. Insoluble impurities were removed by filtration. The filtrate was concentrated under reduced pressure to 1 / 3 of its original volume. The concentrate was then slowly poured into 5 times its volume of anhydrous ethanol, allowed to stand for 2 h, and the solid precipitate was collected by filtration. The precipitate was washed three times with 80% ethanol and dried under vacuum at 40 °C to constant weight to obtain sulfonated lignin.

[0035] S2: Add 12g of sulfonated lignin to 600mL of deionized water, stir at 35℃ and 250r / min, slowly add a small amount of dilute sodium hydroxide solution to adjust the pH to 8, and continue stirring until completely dissolved to obtain a sulfonated lignin solution; add 6g of chlorfenapyr technical to 150mL of solvent oil S-150, stir magnetically at 40℃ until dissolved, and cool to room temperature to obtain a chlorfenapyr oil phase solution.

[0036] Add 6g of chitosan and 1.2L of 1% acetic acid aqueous solution to the reactor. Stir until completely dissolved at 35℃ and 250r / min. Adjust the pH to 4.5 with dilute sodium hydroxide solution and continue stirring. Slowly add 150mL of chlorfenapyr oil phase solution and 3g of emulsifier Tween-80 to the reactor sequentially. After the addition is complete, emulsify for 20min at 700r / min. Then, add 600mL of chitosan dropwise to the reactor over 15min. L of sulfonated lignin solution was stirred for 10 min at 35℃ and 250 r / min. 14 mL of 25% glutaraldehyde solution was added to the reaction vessel, and the pH of the system was adjusted to 6 with dilute sodium hydroxide solution. The reaction was stirred for 1.5 h at the same temperature and speed. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was collected by centrifugation. The precipitate was washed 5 times with deionized water and acetone / ethanol mixed solution, and dried under vacuum at 40℃ to constant weight to obtain chlorfenapyr microcapsule powder.

[0037] S3: 40g of corn stalk biochar was passed through a 60-mesh sieve to remove impurities and dried in an oven at 105℃ for 20h to obtain pretreated biochar. 2.5g of sodium carboxymethyl cellulose (CMC) and 180mL of deionized water were added to a reaction vessel and stirred at 55℃ and 250r / min until completely dissolved. 35g of pretreated biochar was added to the vessel and stirred at the same temperature and speed for 6h to allow CMC molecules to fully diffuse and adsorb onto the surface and pores of the biochar. The mixture was then allowed to stand for 0.8h to allow unloaded CMC molecules to fully settle and age. The residue was collected by filtration and washed with deionized water until the final filtrate was neutral. The residue was then dried at 75℃ to constant weight to obtain modified biochar.

[0038] S4: 8g of modified biochar, 1.5g of sodium lignosulfonate as a dispersant, 0.8g of sodium dodecylbenzenesulfonate as a wetting agent, 4g of ethylene glycol as an antifreeze stabilizer, 0.4g of xanthan gum as a thickener, and 40mL of deionized water were added to a reaction vessel. The mixture was sheared at high speed for 15min at a speed of 700r / min. Then, 25g of chlorfenapyr microcapsule powder was slowly added to the vessel at a temperature of 35℃ and a speed of 150r / min. The mixture was stirred at a constant temperature for 25min to ensure uniform dispersion of the components. After standing for 1h to remove foam, the modified lignin-based slow-release pesticide formulation was obtained.

[0039] Example 3: A modified lignin-based slow-release pesticide formulation, prepared by the following steps: S1: Weigh 1.5g of potassium persulfate and 0.5g of sodium bisulfite and dissolve them in 50mL of deionized water. Stir until dissolved to obtain a potassium persulfate-sodium bisulfite mixed solution. Add 9g of lignin, 90mL of dioxane, and 90mL of deionized water to the reaction vessel. Stir for 1 hour at 65℃ and 350r / min until dissolved. Slowly adjust the pH of the solution to 4.5 with dilute hydrochloric acid. Slowly add 9g of 30% hydrogen peroxide to the vessel. Keep the reaction at the same temperature for 1.2 hours. Raise the temperature to 90℃ and pass the solution through a constant pressure dropping funnel. 90 mL of 1 mol / L sodium allyl sulfonate aqueous solution was added dropwise at a uniform rate over 1.5 h, and 50 mL of potassium persulfate-sodium bisulfite mixed solution was added dropwise simultaneously over 1 h. After the addition was complete, the reaction was continued at the temperature for 1.2 h. After the reaction was completed, the mixture was cooled to room temperature, and the pH of the system was adjusted to 9 with dilute sodium hydroxide. Insoluble impurities were removed by filtration. The filtrate was concentrated under reduced pressure to 1 / 3 of its original volume, and the concentrate was slowly poured into 5 times its volume of anhydrous ethanol. The mixture was allowed to stand for 4 h, and the solid precipitate was collected by filtration. The precipitate was washed three times with 80% ethanol and dried under vacuum at 40 °C to constant weight to obtain sulfonated lignin.

[0040] S2: Add 20g of sulfonated lignin to 1000mL of deionized water, stir at 45℃ and 350r / min, slowly add a small amount of dilute sodium hydroxide solution to adjust the pH to 9, and continue stirring until completely dissolved to obtain a sulfonated lignin solution; add 10g of chlorfenapyr technical to 170mL of solvent oil S-150, stir magnetically at 50℃ until dissolved, and cool to room temperature to obtain a chlorfenapyr oil phase solution.

[0041] Add 10g of chitosan and 2L of 1% acetic acid aqueous solution to the reactor. Stir until completely dissolved at 45℃ and 350r / min. Adjust the pH to 5 with dilute sodium hydroxide solution and continue stirring. Slowly add 170mL of chlorfenapyr oil phase solution and 5g of emulsifier Tween-80 to the reactor sequentially. After the addition is complete, emulsify for 20-30min at 900r / min. Then, add 1000ml of [unspecified solution] dropwise to the reactor over 20min. L of sulfonated lignin solution was stirred for 20 min at 45℃ and 350 r / min. 23 mL of 25% glutaraldehyde solution was added to the reaction vessel, and the pH of the system was adjusted to 6.5 with dilute sodium hydroxide solution. The reaction was stirred for 2 h at the same temperature and speed. After the reaction was completed, the mixture was cooled to room temperature, and the precipitate was collected by centrifugation. The precipitate was washed 5 times with deionized water and acetone / ethanol mixed solution, and then dried under vacuum at 40℃ to constant weight to obtain chlorfenapyr microcapsule powder.

[0042] S3: 60g of corn stalk biochar was passed through a 60-mesh sieve to remove impurities and dried in an oven at 105℃ for 28h to obtain pretreated biochar. 3.4g of sodium carboxymethyl cellulose (CMC) and 220mL of deionized water were added to a reaction vessel and stirred at 65℃ and 350r / min until completely dissolved. 45g of pretreated biochar was added to the vessel and stirred at the same temperature and speed for 6h to allow CMC molecules to fully diffuse and adsorb onto the surface and pores of the biochar. The mixture was then allowed to stand for 1.2h to allow unloaded CMC molecules to settle and age. The residue was collected by filtration and washed with deionized water until the final filtrate was neutral. The residue was then dried at 75℃ to constant weight to obtain modified biochar.

[0043] S4: 12g of modified biochar, 2.5g of sodium lignosulfonate as a dispersant, 1.2g of sodium dodecylbenzenesulfonate as a wetting agent, 6g of ethylene glycol as an antifreeze stabilizer, 0.6g of xanthan gum as a thickener, and 60mL of deionized water were added to a reaction vessel. The mixture was subjected to high-speed shearing at 900r / min for 25min. Then, 35g of chlorfenapyr microcapsule powder was slowly added to the vessel at 45℃ and 250r / min. The mixture was stirred at a constant temperature for 35min to ensure uniform dispersion of the components. After standing for 2h to remove foam, the modified lignin-based slow-release pesticide formulation was obtained.

[0044] The raw materials used in Examples 1-3 of this application are all commercially available products. Sodium bisulfite (purity ≥99.99%), dioxane (purity ≥99%, CAS: 123-91-1), sodium allyl sulfonate (purity ≥90%), ethylene glycol (purity ≥99%), xanthan gum, and lignin were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; chitosan (degree of deacetylation ≥95%, molecular weight 50,000-60,000), sodium lignin sulfonate (molecular weight 5,000-10,000), sodium carboxymethyl cellulose (viscosity: 300-800 mPa·s), and sodium dodecylbenzene sulfonate (purity 95%) were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; potassium persulfate (purity 99.5%) was purchased from Nanjing Chemical Reagent Co., Ltd. The technical grade chlorfenapyr was purchased from Jiangsu Yiheng Pharmaceutical Co., Ltd.; the corn stalk biochar (pyrolyzed at 600℃) was purchased from Guangzhou Zuoke Biotechnology Development Co., Ltd.

[0045] Comparative Example 1: Based on Example 1, step S2, the preparation of chlorfenapyr microcapsule powder, was omitted. In step S4, an equal amount of sulfonated lignin powder and chlorfenapyr technical were directly added, while other steps and parameters remained unchanged, to obtain a slow-release pesticide formulation.

[0046] Comparative Example 2: Based on Example 1, step S1, the preparation of sulfonated lignin, was omitted. In step S2, an equal amount of unmodified lignin was used to replace sulfonated lignin to prepare microcapsules. Other steps and parameters remained unchanged to obtain a slow-release pesticide formulation.

[0047] Comparative Example 3: Based on Example 1, step S3, the preparation of modified biochar, was omitted. In step S4, an equal amount of unmodified corn straw biochar was used to replace the modified biochar, while other steps and parameters remained unchanged, resulting in a slow-release pesticide formulation.

[0048] The performance of the slow-release pesticide formulations prepared in Examples 1-3 and Comparative Examples 1-3 was tested. The suspension rate was tested according to GB / T 14825-2023 standard using the graduated cylinder sedimentation method. 5g of the slow-release pesticide formulations prepared in the examples and comparative examples were placed in a graduated cylinder, diluted with standard hard water and brought to a volume of 250mL. After shaking, the mixture was allowed to stand at 25℃ for 30min. The upper 200mL of suspension was removed, and the content of the active ingredient in the bottom 50mL of precipitate was separated and determined. The suspension rate was calculated. A higher suspension rate indicates better suspension stability of the particles in the formulation and less susceptibility to sedimentation and stratification.

[0049] Storage stability testing includes thermal storage stability testing and cold storage stability testing. Thermal storage stability testing refers to GB / T19136-2021 standard, where each formulation is sealed in an ampoule and stored at a constant temperature of 54℃ for 14 days. Cold storage stability testing refers to GB / T 19137-2003 standard, where each formulation is sealed in an ampoule and stored at a low temperature of 0℃ for 7 days. After storage, the uniformity of the formulation's appearance, pourability, and presence of stratification, crystallization, or precipitation are observed, and the change in suspension rate is measured according to the suspension rate test method described above.

[0050] The controlled-release performance and field efficacy tests were conducted in accordance with GB / T 17980.13-2000 "Guidelines for Field Efficacy Tests of Pesticides". Chinese cabbage was used as the test crop. The controlled-release pesticide formulations prepared in the examples and comparative examples were applied to saline-alkali plots. A water blank control was set up. The pest control effect was investigated at 7, 15, 30 and 45 days after application. The controlled-release and long-lasting efficacy of the formulations were evaluated by observing the efficacy retention at different time points.

[0051] Salt and alkali resistance tests were conducted in a high-salt, high-alkali simulated environment. The slow-release pesticide formulations prepared in the examples and comparative examples were dispersed in simulated saline-alkali water with pH=9.0 and a salt content of 1.5% to prepare a solution with an active ingredient concentration of chlorfenapyr of 50 mg / L. After shaking, the solution was allowed to stand at 25°C for 72 h, and the presence of flocculation or precipitation was observed. If there was no obvious flocculation or precipitation, it indicated that the formulation had good salt and alkali resistance stability.

[0052] Table 1 Performance test results of various slow-release pesticide formulations The performance test results show that the modified lignin-based slow-release pesticide formulations prepared in Examples 1-3 of this invention achieve synergistic optimization of suspension stability, storage stability, slow-release effect, and salt and alkali resistance through a synergistic system of sulfonated lignin modification, microencapsulation, and modified biochar loading. This system effectively improves the application reliability of the formulation in saline-alkali environments while ensuring stable dispersion of the active ingredients, achieving a balance between slow-release and controlled-release and environmental adaptability, and solving the problems of easy failure and short duration of effect of traditional pesticide formulations under saline-alkali conditions.

[0053] Comparative Example 1, which prepared the formulation by directly mixing the active ingredient with the carrier, showed significantly inferior suspension stability, storage stability, and field efficacy compared to the embodiments of this invention. This is because the lack of a microcapsule encapsulation structure resulted in uneven dispersion of the active ingredient in the system, making it prone to crystallization and sedimentation under cold and hot storage conditions. Furthermore, the protective effect of the capsule wall material on the active ingredient was lost, leading to rapid release and loss after field application, resulting in rapid efficacy attenuation. This result demonstrates that the microcapsule encapsulation process employed in this invention plays a crucial supporting role in simultaneously improving the suspension stability and sustained-release long-term efficacy of the formulation.

[0054] Comparative Example 2 omitted the preparation of sulfonated lignin and only used unmodified lignin in the preparation of microcapsules. Its salt and alkali resistance and field efficacy were significantly inferior to those of the Example. This result proves that the anti-alkali interface and electrostatic stabilization provided by sulfonated lignin are important components of the protective system of this invention. Sulfonated lignin modification can not only improve the alkali resistance of the capsule wall and avoid flocculation and destruction in saline-alkali water, but also optimize the interfacial charge characteristics of the microcapsules to form a synergistic dispersion effect with the biochar carrier.

[0055] Comparative Example 3 omitted the modified biochar preparation step and directly used unmodified corn straw biochar to prepare the formulation. Its suspension stability, storage stability and field efficacy persistence were all lower than those of the Example. This indicates that sodium carboxymethyl cellulose modification treatment can not only improve the dispersibility of biochar in water-based systems, but also optimize the interfacial binding effect between microcapsules and carriers, which has a positive effect on improving the suspension stability, storage stability and field sustained release persistence of the formulation.

[0056] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0057] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a modified lignin-based slow-release pesticide formulation, characterized in that, Includes the following steps: Step 1: Using lignin as raw material, it is first activated by hydrogen peroxide, and then subjected to free radical graft copolymerization with sodium allyl sulfonate under the action of an initiator to obtain sulfonated lignin; Step 2: Using sulfonated lignin and chitosan as wall materials and chlorfenapyr as the core, chlorfenapyr microcapsule powder is obtained through emulsification dispersion, electrostatic re-coagulation and glutaraldehyde cross-linking and curing. Step 3: Mix and disperse the modified biochar with chlorfenapyr microcapsule powder, sodium lignosulfonate, sodium dodecylbenzenesulfonate, ethylene glycol, xanthan gum and deionized water to prepare a modified lignin-based slow-release pesticide formulation.

2. The method for preparing a modified lignin-based slow-release pesticide formulation according to claim 1, characterized in that, The ratio of modified biochar, sodium lignosulfonate, sodium dodecylbenzenesulfonate, ethylene glycol, xanthan gum, deionized water, and chlorfenapyr microcapsule powder is 8-12g: 1.5-2.5g: 0.8-1.2g: 4-6g: 0.4-0.6g: 40-60mL: 25-35g.

3. The method for preparing a modified lignin-based slow-release pesticide formulation according to claim 1, characterized in that, The specific preparation steps of the acaricide microcapsule powder are as follows: Chitosan and a 1% (w / w) aqueous acetic acid solution were added to a reaction vessel and stirred at 35-45℃ and 250-350 rpm until dissolved. The pH was adjusted to 4.5-5 with dilute sodium hydroxide solution, and stirring was continued. The chlorfenapyr oil phase solution and emulsifier Tween-80 were slowly added to the vessel in sequence. After the addition was complete, emulsification was carried out at 700-900 rpm for 20-30 min. Then, sulfonated lignin solution was added dropwise to the vessel within 15-20 min. The reaction was stirred at 35-45℃ and 250-350 rpm for 10-20 min. A 25% (w / w) glutaraldehyde solution was added to the vessel, and the pH of the system was adjusted to 6-6.5 with dilute sodium hydroxide solution. The reaction was stirred at the same temperature and speed for 1.5-2 h. After cooling to room temperature, the precipitate was collected by centrifugation, washed, and dried to obtain chlorfenapyr microcapsule powder.

4. The method for preparing a modified lignin-based slow-release pesticide formulation according to claim 3, characterized in that, The ratio of chitosan, acetic acid aqueous solution, chlorfenapyr oil phase solution, emulsifier Tween-80, sulfonated lignin solution and 25% glutaraldehyde solution is 6-10g: 1.2-2L: 150-170mL: 3-5g: 600-1000mL: 14-23mL.

5. The method for preparing a modified lignin-based slow-release pesticide formulation according to claim 3, characterized in that, The sulfonated lignin solution is prepared by mixing sulfonated lignin and deionized water at a ratio of 12-20g:600-1000mL; the chlorfenapyr oil phase solution is prepared by mixing chlorfenapyr technical and solvent oil S-150 at a ratio of 6-10g:150-170mL.

6. The method for preparing a modified lignin-based slow-release pesticide formulation according to claim 3, characterized in that, The specific preparation steps of the sulfonated lignin are as follows: Lignin, dioxane, and deionized water were added to a reaction vessel and stirred at 55-65℃ and 250-350 r / min until dissolved. The pH of the solution was slowly adjusted to 3.5-4.5 with dilute hydrochloric acid. Hydrogen peroxide with a mass fraction of 30% was slowly added to the vessel and the reaction was maintained at the same temperature for 0.8-1.2 h. The temperature was raised to 80-90℃, and sodium allyl sulfonate aqueous solution with a concentration of 1 mol / L was added dropwise at a uniform rate over 1.5 h through a constant pressure dropping funnel. A potassium persulfate-sodium bisulfite mixed solution was added dropwise simultaneously over 1 h. After the addition was completed, the reaction was maintained at the same temperature for 0.8-1.2 h. After the reaction was completed, the mixture was cooled to room temperature, and the pH of the system was adjusted to 8-9 with dilute sodium hydroxide. The mixture was filtered to remove impurities, and the filtrate was concentrated under reduced pressure to 1 / 3 of its original volume. The concentrate was then slowly poured into 5 times its volume of anhydrous ethanol and allowed to stand for 2-4 h. The precipitate was collected by filtration, washed, and dried to obtain sulfonated lignin. The ratio of lignin, dioxane, deionized water, 30% hydrogen peroxide, 1 mol / L sodium allyl sulfonate aqueous solution, and potassium persulfate-sodium bisulfite mixed solution is 6-9 g: 60-90 mL: 60-90 mL: 6-9 g: 60-90 mL: 40-50 mL.

7. The method for preparing a modified lignin-based slow-release pesticide formulation according to claim 6, characterized in that, The potassium persulfate-sodium bisulfite mixed solution is prepared by mixing potassium persulfate, sodium bisulfite and deionized water in a ratio of 1-1.5g:0.4-0.5g:40-50mL.

8. The method for preparing a modified lignin-based slow-release pesticide formulation according to claim 1, characterized in that, The specific preparation steps of the modified biochar are as follows: Sodium carboxymethyl cellulose and deionized water were added to a reaction vessel and stirred at 55-65℃ and 250-350 r / min until dissolved. Pretreated biochar was then added to the vessel and stirred for 6 hours. The mixture was then allowed to stand for 0.8-1.2 hours, filtered, washed, and dried to obtain modified biochar. The ratio of sodium carboxymethyl cellulose, deionized water, and pretreated biochar is 2.5-3.4g: 180-220mL: 35-45g.

9. The method for preparing a modified lignin-based slow-release pesticide formulation according to claim 8, characterized in that, The pretreated biochar was prepared by passing 40-60g of corn stalk biochar through a 60-mesh sieve to remove impurities and drying it at 105℃ for 20-28h.

10. A modified lignin-based slow-release pesticide formulation, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.

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