Straw-based regular molecular weight lignosulfonate fractionation refining method for pesticide dispersant and application

Abstract

The application discloses a straw-based regular molecular weight lignin sulfonate grading refining method for pesticide dispersants and application, and the method is characterized in that: taking wheat straw or corn straw as raw material, crude lignin is extracted and modified to prepare lignin sulfonate, and then a gradient ultrafiltration grading refining process is adopted to accurately separate lignin sulfonate fractions with multiple molecular weight distribution, regular molecular structure and uniform molecular structure, so that the industry pain points of traditional straw lignin sulfonate, such as large molecular weight span, mixed components, unstable performance and poor targeted adaptability, are solved. Through the grading refining, the accurate regulation of the molecular weight of the lignin sulfonate is realized, different molecular weight fractions can adapt to the dispersing requirements of different types of pesticide formulations, and the refined regular lignin sulfonate prepared for the pesticide dispersants has the advantages of high particle dispersion uniformity, excellent leaf wetting property, strong formulation storage stability and the like, and can significantly improve the utilization rate of the pesticide.

Description

Technical Field

[0001] This invention belongs to the technical fields of biomass waste refining and processing, polymer fractionation and separation, and agricultural green adjuvants. Specifically, it relates to a method and application for fractionation and refining of straw-based regular molecular weight lignin sulfonate for pesticide dispersants. Background Technology

[0002] Wheat straw and corn straw are the most abundant agricultural and forestry biomass wastes in my country. Lignin, as one of the core components of straw, is used to prepare lignin sulfonates through sulfonation modification. These lignin sulfonates are a core green raw material that can replace traditional chemical synthetic dispersants and are widely used in the formulation processing of pesticides, such as aqueous suspensions and wettable powders. However, existing straw lignin sulfonate preparation processes can only produce crude products without fine grading. The resulting products suffer from core defects such as extremely wide molecular weight distribution, mixed large and small molecular components, and low molecular regularity.

[0003] In crude straw lignin sulfonates, the ultra-large molecular weight components easily lead to pesticide particle agglomeration and formulation sedimentation and stratification, while the small molecular weight components have insufficient surface activity and poor dispersion stability. The inconsistent molecular weight distribution results in large batch-to-batch variations in product performance, making it impossible to precisely adapt to the dispersion requirements of pesticides with different particle sizes and polarities. This significantly limits the large-scale application of straw lignin in high-end pesticide adjuvants. Currently, industry research on straw lignin sulfonates focuses primarily on modification process optimization, lacking mature and efficient molecular weight fractionation and refining technologies. This makes it difficult to obtain graded products with regular molecular weight and stable performance, hindering the refined and high-value utilization of lignin sulfonates.

[0004] While some literature reports the use of ultrafiltration membranes for lignin fractionation, existing fractionation technologies only focus on separation and purification, failing to establish a targeted correlation between the molecular weight characteristics of the fractionated products and the application requirements of pesticide formulations. The mechanisms of action of lignin sulfonates of different molecular weight fractions in pesticide dispersion systems are drastically different—high molecular weight fractions primarily stabilize particles through steric hindrance, medium molecular weight fractions possess both steric hindrance and surface activity, while low molecular weight fractions mainly rely on electrostatic repulsion and solubilization. Using the wrong fraction in the wrong system not only fails to deliver performance advantages but may even lead to deterioration of formulation performance. This invention, based on the aforementioned understanding of the structure-activity relationship between molecular weight, performance, and application, proposes a technical solution integrating fractionation purification and targeted application.

[0005] To address the gaps and deficiencies in existing technologies, this invention innovatively employs a straw lignin sulfonation modification coupled with gradient ultrafiltration for graded purification. By precisely screening ultrafiltration membranes with different molecular weight cutoffs, and separating and purifying step by step, multiple lignin sulfonate fractions with narrow molecular weight distributions, regular molecular structures, and low impurity content are obtained. Based on the performance differences of different molecular weight components, these fractions can be specifically applied to different pesticide formulation systems, fundamentally solving the problems of unstable dispersion performance and poor compatibility of crude lignin sulfonates, and realizing the refined and high-value utilization of straw lignin resources. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for the graded purification of straw-based regular molecular weight lignin sulfonate for pesticide dispersants and its application.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0008] The core differences between this invention and existing grading technologies are as follows: First, this invention does not simply grade and separate lignin, but rather precisely designs a molecular weight cutoff combination of 10000 / 5000 / 1000 Da three-stage ultrafiltration membranes to meet the specific application requirements of pesticide dispersants. This allows the molecular weight distribution coefficient (PDI) of each fraction to be precisely controlled within the range of 1.1-1.2, achieving a high degree of molecular weight regularization. Second, this invention reveals for the first time the targeted compatibility relationship between different molecular weight fractions of straw-based lignin sulfonate and different types of pesticide formulations, establishing a complete technology chain of "grading-screening-targeted application". Third, this invention discovers that the combination of high molecular weight fractions and medium molecular weight fractions in a specific ratio can produce synergistic effects, while simultaneously improving the storage stability and leaf wetting performance of the formulation. This combination strategy differs from existing technologies that only retain high molecular weight fractions, and also from those that only retain low molecular weight fractions.

[0009] The first objective of this invention is to provide a method for the graded purification of straw-based regular molecular weight lignin sulfonates for pesticide dispersants, comprising the following steps:

[0010] S1. Straw pretreatment and crude lignin extraction: Wheat straw or corn straw is washed, dried, crushed, and sieved to obtain straw powder; the straw powder is mixed with 8%-12% sodium hydroxide solution at a solid-liquid ratio of 1:8-1:12 g / mL, stirred at 80-90℃ for 2-4 hours, filtered to remove residue, and the filtrate is collected; the pH of the filtrate is adjusted to 2.0-3.0, allowed to stand to precipitate, centrifuged, washed, and dried to obtain crude straw lignin;

[0011] S2. Lignin sulfonation modification: Disperse crude lignin from straw in deionized water to prepare an aqueous suspension with a mass fraction of 15%-25%. Adjust the pH to 10.0-11.0, add 37% formaldehyde solution and sodium sulfite, and reflux at 90-105℃ for 3-5 hours to complete the sulfonation modification. Cool and filter to obtain crude lignin sulfonate mother liquor.

[0012] S3. Gradient ultrafiltration and purification: The crude lignin sulfonate mother liquor is diluted to a mass fraction of 3%-5%. Under the conditions of temperature 25-35℃ and pressure 0.2-0.4MPa, a multi-stage gradient ultrafiltration membrane is used to perform gradient ultrafiltration circulation filtration in order of molecular weight from large to small, and three groups of lignin sulfonate intercepted liquids with regular molecular weights of large, medium and small are obtained respectively.

[0013] S4. Post-processing and refining: The three groups of lignin sulfonate intercepting liquids with regular molecular weights are concentrated and spray-dried to obtain high molecular weight lignin sulfonate fractions, medium molecular weight lignin sulfonate fractions, and low molecular weight lignin sulfonate fractions.

[0014] The high molecular weight fraction of lignin sulfonate is used in pesticide suspensions with a solid content of 40%-50%, the medium molecular weight fraction of lignin sulfonate is used in pesticide suspensions with a solid content of 5%-40%, and the low molecular weight fraction of lignin sulfonate is used in pesticide solubles with a viscosity ≤10 mPa·s.

[0015] Preferably, in step S1, the straw drying temperature is 55-65℃, the straw is dried to a moisture content of ≤5%, and after crushing, it is passed through a 40-60 mesh sieve; it is allowed to stand and settle for 4-6 hours, and the centrifugation speed is 8000-10000 r / min, and the centrifugation time is 10-15 min.

[0016] Preferably, in step S2, the mass ratio of lignin, 37% formaldehyde solution, and anhydrous sodium sulfite is 100:8:15-100:12:25; the degree of sulfonation of the crude lignin sulfonate obtained by sulfonation modification is 1.2-2.0 mmol / g.

[0017] Preferably, in step S3, the gradient ultrafiltration cycle is repeated 2-3 times. After multi-stage gradient ultrafiltration, the membrane module is rinsed with deionized water to recover the adsorbed effective components, with a total fraction recovery rate ≥90%. The preparation of the three molecular weight regular lignin sulfonate fractions is as follows:

[0018] S31, High molecular weight fractionation: The mother liquor is retained using a 10000 Da ultrafiltration membrane, and the retained liquor is concentrated to obtain high molecular weight lignin sulfonate with a molecular weight of 10000-30000 Da and a molecular weight distribution coefficient PDI≤1.2.

[0019] S32. Preparation of medium molecular weight fraction: A 5000 Da ultrafiltration membrane was used to retain 10000 Da of the ultrafiltration membrane permeate. The retained solution was concentrated to obtain medium molecular weight lignin sulfonate with a molecular weight of 5000-10000 Da and a molecular weight distribution coefficient PDI≤1.15.

[0020] S33. Preparation of low molecular weight fractions: A 1000 Da ultrafiltration membrane is used to retain the 5000 Da ultrafiltration membrane permeate. The retained solution is concentrated to obtain low molecular weight lignin sulfonates with a molecular weight of 1000-5000 Da and a molecular weight distribution coefficient (PDI) ≤ 1.1.

[0021] A second objective of this invention is to provide a pesticide dispersant composition comprising high molecular weight fractional lignin sulfonate and medium molecular weight fractional lignin sulfonate prepared by the method, wherein the mass ratio of the high molecular weight fractional lignin sulfonate to the medium molecular weight fractional lignin sulfonate is 1:2-3:1.

[0022] Preferably, the mass ratio of the high molecular weight fraction of lignin sulfonate to the medium molecular weight fraction of lignin sulfonate is 2:1.

[0023] Preferably, the total amount of straw-based lignin sulfonate added in the pesticide dispersant composition is 2.0%-4.5% of the total mass of the pesticide dispersant.

[0024] Preferably, the pesticide dispersant composition is used to prepare aqueous suspensions, wettable powders, water-dispersible granules, or soluble concentrates.

[0025] Preferably, the high molecular weight fraction of lignin sulfonate and the medium molecular weight fraction of lignin sulfonate work synergistically to exert a steric stabilization effect and improve leaf wetting and adhesion properties, resulting in a median particle size D50 ≤ 3.2 μm, a particle size distribution span SPAN ≤ 1.1, a suspension rate ≥ 94% after 30 days of storage at room temperature, and a static contact angle of the pesticide solution on crop leaves ≤ 40°.

[0026] A third objective of this invention is to provide the application of the aforementioned pesticide dispersant composition in the preparation of pesticide dispersants.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1. This invention achieves precise control of the molecular structure of lignin sulfonate: For the first time, a specific three-level gradient ultrafiltration membrane combination (10000 / 5000 / 1000 Da) was used to successfully separate straw-derived lignin sulfonate into well-ordered fractions with a molecular weight distribution coefficient (dispersion) as low as about 1.1, which completely overturns the inherent property of disordered molecular weight of traditional products and fills the gap in the field of fine classification.

[0029] 2. This invention reveals the targeted structure-activity relationship of molecular weight, performance, and application, and enables precise application:

[0030] The strong steric hindrance effect of high molecular weight fractions (10,000-30,000 Da) was verified, making them ideal dispersants for preparing high-sustaining and long-term stable aqueous suspensions.

[0031] The optimal hydrophilic-lipophilic balance value for the medium molecular weight fraction (5000-10000 Da) was discovered, which unexpectedly reduced the contact angle of the pesticide solution on the hydrophobic leaf surface to below 40°, solving the global problem of pesticide wetting and spreading on the leaf surface.

[0032] The unparalleled uniform dispersion capability of small molecular weight fractions (1000-5000 Da) in low viscosity, fine particle size systems was confirmed.

[0033] This tiered-targeted application strategy enables the precise design and control of pesticide formulation performance.

[0034] 3. The performance of this invention significantly surpasses that of existing products: Comparative experiments irrefutably demonstrate that the regular fraction of this invention has an overwhelming advantage over ungraded crude products and mainstream commercial products in core performance aspects such as formulation suspension rate (>94% vs. <88%), particle size distribution width (SPAN<1.1 vs. >1.4), and leaf surface wettability (contact angle <40° vs. >50°), and also possesses excellent processing performance such as low foaming and easy redispersibility.

[0035] 4. The process of this invention is green, economical, and highly adaptable to industrialization: it involves physical separation throughout the entire process, with zero chemical additives and zero secondary pollution. The process is modular, with mild and controllable parameters, and a high total product recovery rate. It can be directly integrated into existing lignin processing production lines to achieve large-scale, low-cost, and high-value production. Attached Figure Description

[0036] Figure 1 This is a GPC (gel permeation chromatography) elution curve of the large, medium and small molecular weight regular fractions prepared in Example 1 of the present invention.

[0037] Figure 2 This is a comparison chart of the particle size distribution of 25% imidacloprid aqueous suspension prepared from high molecular weight fraction of Example 1, crude product of Comparative Example 1, and commercially available product of Comparative Example 2.

[0038] Figure 3 a is a static contact angle photograph of the molecular weight fraction on the leaves of different crops (cucumber, cabbage, rice) in Example 2 of this invention.

[0039] Figure 3b is a schematic diagram of the static contact angle of molecular weight fractions on the leaves of different crops (cucumber, cabbage, rice) in Embodiment 2 of the present invention. Detailed Implementation

[0040] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0041] Example 1: Grading and refining of corn straw-derived lignin sulfonate with regular molecular weight and its product indicators.

[0042] S1. Straw pretreatment for lignin extraction: Select dry, mold-free corn straw, dry it at 60℃ to a moisture content of 4%, and crush it through a 50-mesh sieve; take 100g of straw powder, add 1000mL of 10% sodium hydroxide solution (solid-liquid ratio 1:10), stir and react at 85℃ for 3h, filter to remove residue while hot; adjust the pH of the filtrate to 2.5 with 3M dilute hydrochloric acid, let it stand to precipitate for 5h, centrifuge at 9000r / min for 12min, wash the precipitate with deionized water until neutral, and vacuum dry at 50℃ to obtain 29.6g of purified corn straw crude lignin.

[0043] S2. Preparation of crude product by sulfonation modification: Take 100g of crude lignin, prepare a 20% aqueous suspension, adjust the pH to 10.5 with 30% sodium hydroxide solution, add 10g of 37% formaldehyde solution and 20g of anhydrous sodium sulfite, and reflux at 100℃ for 4h. After cooling, remove a small amount of insoluble matter by vacuum filtration with qualitative filter paper to obtain a clear crude lignin sulfonate mother liquor.

[0044] S3. Gradient Ultrafiltration and Purification: Dilute the mother liquor to 4% by mass and perform gradient ultrafiltration at 30℃ and 0.3MPa operating pressure. First, pass the solution through a 10000 Da polyethersulfone (PES) membrane module for three cycles of filtration, collecting retentate A. Then, pass the permeate through a 5000 Da PES membrane for three cycles of filtration, collecting retentate B. Finally, pass the permeate through a 1000 Da PES membrane for three cycles of filtration, collecting retentate C. Before each membrane module switch, rinse the previous stage membrane with deionized water and collect the rinse solution, adding it to the corresponding retentate.

[0045] S4. Post-processing purification: Residues A, B, and C were concentrated under vacuum at 60°C to a solid content of approximately 15%, and then spray-dried at an inlet air temperature of 190°C and an outlet air temperature of 85°C, yielding brown powders of high molecular weight regular fraction (LS-H, 16.3 g), medium molecular weight regular fraction (LS-M, 12.8 g), and low molecular weight regular fraction (LS-L, 9.1 g), respectively. The overall fraction recovery rate was 92.1%.

[0046] Product characterization data:

[0047] LS-H: weight-average molecular weight Mw = 18200 Da, number-average molecular weight Mn = 15420 Da, dispersibility PDI = 1.18, degree of sulfonation 1.52 mmol / g.

[0048] LS-M: weight-average molecular weight Mw = 7150 Da, number-average molecular weight Mn = 6380 Da, dispersibility PDI = 1.12, degree of sulfonation 1.65 mmol / g.

[0049] LS-L: weight-average molecular weight Mw = 2850 Da, number-average molecular weight Mn = 2640 Da, dispersibility PDI = 1.08, degree of sulfonation 1.71 mmol / g.

[0050] Example 2: Grading and refining of wheat straw-derived lignin sulfonate with regular molecular weight.

[0051] S1. Straw Pretreatment and Crude Lignin Extraction: Dry, mold-free wheat straw was selected, soaked and rinsed with water to remove surface dirt, leaves, and other impurities. It was then dried at 60℃ to a moisture content of 4%, pulverized, and passed through a 40-mesh sieve to obtain wheat straw powder. 100g of straw powder was added to 1200mL of a 12% sodium hydroxide solution (solid-liquid ratio 1:12 g / mL), and the mixture was stirred at 80℃ for 4 hours. After the reaction, the mixture was filtered while hot through a 200-mesh nylon filter cloth to remove cellulose and hemicellulose residues, and the black liquor filtrate was collected. The filtrate was slowly adjusted to pH 2.0 with 3M dilute hydrochloric acid under stirring. After standing for 6 hours to precipitate, it was centrifuged at 10000r / min for 10 minutes, the supernatant was discarded, and the precipitate was repeatedly washed with deionized water until the pH of the washing liquid was neutral. The precipitate was then vacuum dried at 50℃ for 24 hours to obtain 28.1g of crude wheat straw lignin.

[0052] S2. Preparation of crude lignin sulfonate by lignin sulfonation modification: Take 100g of the above-mentioned crude lignin from wheat straw, disperse it in deionized water, and prepare a lignin suspension with a mass fraction of 25%. Adjust the pH of the system to 11.0 by adding 30% sodium hydroxide solution while stirring. Then, add 8g of 37% formaldehyde solution and 15g of anhydrous sodium sulfite sequentially, with a mass ratio of lignin, 37% formaldehyde solution, and anhydrous sodium sulfite of 100:8:15. After stirring evenly, heat to 95℃ and reflux for 5 hours to complete the sulfonation modification. After the reaction, cool to room temperature and filter with qualitative filter paper to remove a small amount of insoluble impurities, obtaining an ungraded crude wheat straw lignin sulfonate mother liquor.

[0053] S3. Gradient ultrafiltration staged purification (core purification step): The above crude lignin sulfonate mother liquor is diluted with deionized water to a mass fraction of 3.5%, and after standing at room temperature for 2 hours to remove bubbles, it is pressurized and staged filtered using a multi-stage gradient ultrafiltration membrane module at a temperature of 28℃ and an operating pressure of 0.35MPa.

[0054] S31. High molecular weight regular fractionation: First, a polyethersulfone (PES) ultrafiltration membrane with a molecular weight cutoff of 10,000 Da is used for filtration, and the mixture is circulated and filtered twice. The retentate A is collected. After filtration, the membrane module is rinsed with deionized water, and the rinsing solution is added to the retentate A to obtain a high molecular weight lignin sulfonate solution.

[0055] S32. Medium molecular weight regular fraction: The permeate from the 10000 Da membrane is filtered through a PES ultrafiltration membrane with a molecular weight cutoff of 5000 Da, and the mixture is circulated and filtered twice. The retentate B is collected. After filtration, the membrane module is rinsed with deionized water, and the rinsing solution is added to the retentate B to obtain a medium molecular weight lignin sulfonate solution.

[0056] S33. Low molecular weight regular fraction: The permeate from the 5000 Da membrane is filtered using a PES ultrafiltration membrane with a molecular weight cutoff of 1000 Da. The filtration is repeated twice, and the retentate C is collected. After filtration, the membrane module is rinsed with deionized water, and the rinsing solution is added to the retentate C to obtain a low molecular weight lignin sulfonate solution.

[0057] S4. Post-fractional processing: Retained solutions A, B, and C were concentrated under vacuum at 60°C to a solid content of approximately 15%, and then spray-dried. The inlet air temperature for spray drying was 190°C, and the outlet air temperature was 85°C, yielding brown powders of high molecular weight regular fraction (LS-H, 15.8 g), medium molecular weight regular fraction (LS-M, 12.2 g), and low molecular weight regular fraction (LS-L, 8.9 g), respectively. The total mass of the three fractions was calculated to be 36.9 g. Based on the solid content analysis of an intermediate sample of the crude mother liquor before fractionation, the estimated total solids mass was approximately 40.8 g, resulting in an overall fractionation recovery rate of 90.5%.

[0058] Product characterization data:

[0059] Large molecular weight regular fraction (LS-H): weight average molecular weight Mw = 16800 Da, number average molecular weight Mn = 14118 Da, molecular weight distribution index (PDI) = 1.19, degree of sulfonation 1.48 mmol / g.

[0060] Medium molecular weight regular fraction (LS-M): weight average molecular weight Mw = 7050 Da, number average molecular weight Mn = 6239 Da, molecular weight distribution index (PDI) = 1.13, degree of sulfonation 1.61 mmol / g.

[0061] Small molecular weight regular fraction (LS-L): weight average molecular weight Mw = 2720 Da, number average molecular weight Mn = 2495 Da, molecular weight distribution index (PDI) = 1.09, degree of sulfonation 1.73 mmol / g.

[0062] Example 3: Application of grading and fractionation in the preparation of various pesticide formulations.

[0063] This embodiment demonstrates the targeted adaptation application of the three groups of regular molecular weight fractions (large, medium, and small) prepared in Example 1 in different types of pesticide formulations.

[0064] 3-1, 40% Chlorothalonil aqueous suspension (high solids content (40%-50%), bactericide).

[0065] The high molecular weight regular fraction LS-H from Example 1 was used as a dispersant, and the amount added was 4.0% of the total mass of the formulation.

[0066] Formulation (by mass percentage): Chlorothalonil technical (98% active ingredient content) 40.8%, LS-H dispersant 4.0%, ethylene glycol (antifreeze) 5.0%, xanthan gum (thickener) 0.15%, magnesium aluminum silicate (suspending agent) 0.5%, organosilicon defoamer 0.3%, deionized water to 100%.

[0067] Formulation preparation process: Deionized water, ethylene glycol, LS-H dispersant, and defoamer are mixed and stirred evenly. Chlorothalonil technical grade is added, and the mixture is dispersed by high-speed shearing for 20 minutes. Then, it is transferred to a horizontal sand mill, and zirconia beads (particle size 1.0-1.2 mm) are added. The mill speed is controlled at 2000 r / min, and the mixture is ground until the median particle size D50 ≤ 2.5 μm. After discharge, xanthan gum and magnesium aluminum silicate are added, and the mixture is homogenized by low-speed stirring for 30 minutes to obtain a 40% chlorothalonil aqueous suspension.

[0068] 3-2.5% abamectin salt dispersible granules (WDG, insecticide).

[0069] The medium molecular weight regular fraction LS-M from Example 1 was used as a dispersant, and the amount added was 3.5% of the total mass of the formulation.

[0070] Formulation (by mass percentage): 6.7% (5% by weight) of emamectin benzoate technical grade (75% active ingredient content), 3.5% of LS-M dispersant, 60% of diatomaceous earth (carrier filler), 8% of ammonium sulfate (disintegrant), 1.5% of naphthalenesulfonate formaldehyde condensate (wetting agent), appropriate amount of soluble starch (binder), and kaolin to make up to 100%.

[0071] Formulation preparation process: Weigh all solid materials according to the formula, then mix and pulverize them in an air jet mill until a fineness of ≥98% passes through a 325-mesh sieve. Transfer the pulverized mixture to a kneader, add an appropriate amount of deionized water, and knead until the material forms plastic lumps. Feed the lumps into an extrusion granulator and granulate them through a 0.8mm sieve. The wet granules are then dried in a fluidized bed dryer at 60℃ until the moisture content is ≤2%, and then graded through a 10-40 mesh sieve to obtain 5% abamectin salt dispersible granules.

[0072] 3-3, 1% brassinolide soluble concentrate (SL, plant growth regulator).

[0073] The low molecular weight regular fraction LS-L from Example 1 was used as a solubilizing and dispersing agent, and the amount added was 2.5% of the total mass of the formulation.

[0074] Formulation (by mass percentage): 1.1% (1% by mass) of 24-epibrassinolide technical (92% active ingredient content), 2.5% LS-L solubilizer and dispersant, 15% ethanol (solvent), and deionized water to bring the total to 100%.

[0075] Formulation preparation process: Brassinolide technical grade drug was dissolved in ethanol and stirred until completely dissolved to obtain the oil phase. LS-L was dissolved in deionized water and stirred until completely dissolved to obtain the aqueous phase. Under high-speed shear stirring, the oil phase was slowly added to the aqueous phase, and shearing and homogenization continued for 15 min to obtain a clear and homogeneous 1% brassinolide soluble concentrate.

[0076] Example 4: Graded and graded compound application.

[0077] 30% Pyraclostrobin·Difenoconazole Aqueous Suspension Concentrate (Compound Fungicide)

[0078] This embodiment demonstrates the combined use of high molecular weight fractions and medium molecular weight fractions to achieve optimal overall performance. The high molecular weight regular fraction LS-H and the medium molecular weight regular fraction LS-M from Example 1 are combined at a mass ratio of 2:1 as a dispersant, with a total addition amount of 3.5% of the total mass of the formulation (of which LS-H accounts for 2.33% and LS-M accounts for 1.17%).

[0079] Formulation (by mass percentage): 15.3% (15% of pyraclostrobin technical grade, 98% active ingredient content), 15.5% (15% of difenoconazole technical grade, 97% active ingredient content), 2.33% LS-H dispersant, 1.17% LS-M dispersant, 5.0% ethylene glycol (antifreeze), 0.12% xanthan gum (thickener), 0.4% magnesium aluminum silicate (suspending agent), 0.2% sodium benzoate (preservative), 0.3% silicone defoamer, and deionized water to 100%.

[0080] Formulation preparation process: Deionized water, ethylene glycol, LS-H and LS-M dispersants, and defoamer are mixed and stirred evenly. Pyraclostrobin and difenoconazole technical materials are added, and the mixture is pre-dispersed under high-speed shear for 30 minutes. The pre-dispersed slurry is transferred to a horizontal sand mill, and zirconia beads (particle size 1.0-1.2 mm) are added. The mixture is circulated and ground at 2000 r / min until the median particle size D50 ≤ 2.0 μm. After discharge, xanthan gum, magnesium aluminum silicate, and sodium benzoate are added, and the mixture is homogenized under low-speed stirring for 1 hour to obtain a 30% pyraclostrobin·difenoconazole aqueous suspension.

[0081] This compound formulation aims to synergistically leverage the powerful steric stabilization effect of LS-H and the excellent leaf wetting and spreading properties of LS-M, enabling the formulation to possess both long-term storage stability and excellent wetting and adhesion capabilities during field application.

[0082] Comparative Example 1: Crude lignin sulfonate from ungraded straw.

[0083] The same straw pretreatment, extraction, and sulfonation modification process as in Example 1 was used, but without any ultrafiltration grading and refining treatment, and the ungraded crude lignin sulfonate was obtained by direct drying.

[0084] S1. Straw pretreatment and crude lignin extraction: The steps are exactly the same as in Example 1 S1, and 29.6g of purified corn straw crude lignin is obtained.

[0085] S2. Preparation of crude lignin sulfonate by lignin sulfonation modification: The steps are exactly the same as in Example 1, S2, to obtain crude lignin sulfonate mother liquor. This mother liquor is not subjected to subsequent ultrafiltration fractionation.

[0086] S3. Direct drying: The crude lignin sulfonate mother liquor was directly vacuum concentrated at 60°C to a solid content of about 20%, and then spray dried with an inlet air temperature of 190°C and an outlet air temperature of 85°C to obtain 38.1g of ungraded crude lignin sulfonate brown powder.

[0087] Product characterization data: Weight-average molecular weight (Mw) = 10500 Da, with an extremely wide molecular weight distribution, covering a range of 1000-30000 Da, and a molecular weight distribution index (PDI) of 1.85. The product composition is disordered, containing macromolecular, medium-molecular, and small-molecular components, with an average degree of sulfonation of 1.55 mmol / g.

[0088] This comparative example demonstrates that products obtained without the gradient ultrafiltration fractionation purification process of this invention have a wide molecular weight distribution and mixed components, which contrasts sharply with the regular fractionation of this invention.

[0089] Comparative Example 2: Commercial sodium lignosulfonate dispersant.

[0090] The product uses commercially available VSI type sodium lignosulfonate, manufactured by Shandong Wantu Polymer Materials Co., Ltd. This product is a commercially available, general-purpose sodium lignosulfonate dispersant obtained from papermaking black liquor through sulfonation modification and spray drying. It is not derived from straw and has not undergone molecular weight fractionation refining.

[0091] The product was purchased directly from the supplier and is a brownish-yellow powder. No further processing or grading was performed before use.

[0092] Product specifications: pH value (1% aqueous solution) 8.5-10.0, water-insoluble matter ≤1.5%, sulfate content ≤5.0%, reducing agent content ≤6.0%, water content ≤7.0%. Product weight-average molecular weight range is 8000-15000 Da.

[0093] Measured characterization data: weight-average molecular weight Mw = 11800 Da, molecular weight distribution coefficient (PDI) = 2.35, degree of sulfonation 1.38 mmol / g.

[0094] This comparative example represents the performance level of conventional ungraded lignin sulfonate dispersants currently available on the market, and is used to compare the performance with that of the graded and refined product of this invention.

[0095] Comparative Example 3: Using a single medium molecular weight fraction in a high solids content (40%-50%) system.

[0096] In the 40% chlorothalonil aqueous suspension (high solids content pesticide formulation), the high molecular weight regular fraction LS-H was not used, but the medium molecular weight regular fraction LS-M, in the same amount as in Example 3-1, was used as the dispersant to demonstrate the irreplaceable nature of high molecular weight fractions for high solids content systems.

[0097] The formulation and preparation process were exactly the same as those in Example 3-1, except that the 4.0% LS-H (the high molecular weight fraction of Example 1) in Example 3-1 was replaced with 4.0% LS-M (the medium molecular weight fraction of Example 1).

[0098] Specific formula (by mass percentage): 40.8% chlorothalonil technical (98% active ingredient content), 4.0% LS-M dispersant, 5.0% ethylene glycol (antifreeze), 0.15% xanthan gum (thickener), 0.5% magnesium aluminum silicate (suspending agent), 0.3% silicone defoamer, and deionized water to make up to 100%.

[0099] Preparation process: Deionized water, ethylene glycol, LS-M dispersant, and defoamer are mixed and stirred evenly. Chlorothalonil technical grade is added, and the mixture is dispersed by high-speed shearing for 20 minutes. The mixture is then transferred to a horizontal sand mill, and zirconia beads (particle size 1.0-1.2 mm) are added. The mill is ground at 2000 r / min until the median particle size D50 ≤ 2.5 μm. After discharge, xanthan gum and magnesium aluminum silicate are added, and the mixture is homogenized by low-speed stirring for 30 minutes to obtain a 40% chlorothalonil aqueous suspension.

[0100] This comparative example is used to verify whether medium molecular weight fractions can replace high molecular weight fractions under the same solid content conditions, thereby highlighting the uniqueness and necessity of the strong steric stabilizing effect of high molecular weight fractions in high solid content systems.

[0101] Comparative Example 4: Samples separated using only a 10000 Da membrane in a single stage.

[0102] This comparative example uses only a single-stage ultrafiltration membrane for coarse separation, without multi-stage gradient separation, to demonstrate the necessity of multi-stage gradient ultrafiltration purification for obtaining well-ordered fractions with low dispersion (≤1.2).

[0103] S1. Straw pretreatment and crude lignin extraction: The steps are exactly the same as in Example 1 S1, and 29.6g of purified corn straw crude lignin is obtained.

[0104] S2. Preparation of crude lignin sulfonate by lignin sulfonation modification: The steps are exactly the same as in Example 1 S2, and crude lignin sulfonate mother liquor is obtained.

[0105] S3. Single-stage ultrafiltration separation: The crude lignin sulfonate mother liquor is diluted with deionized water to a mass fraction of 4%. Under conditions of 30°C and 0.3 MPa, separation is achieved solely through a polyethersulfone (PES) ultrafiltration membrane with a molecular weight cutoff of 10000 Da. The process is repeated three times, and the retentate is collected. Subsequent 5000 Da and 1000 Da membrane fractionation is not performed. After filtration, the membrane module is rinsed with deionized water, and the rinsing solution is added to the retentate.

[0106] S4. Post-processing: The retentate was vacuum concentrated at 60°C to a solid content of about 15%, and then spray-dried at an inlet air temperature of 190°C and an outlet air temperature of 85°C to obtain 20.1g of brown powder with a single-stage separation fraction of >10000 Da.

[0107] Product characterization data: weight-average molecular weight Mw = 21500 Da, number-average molecular weight Mn = 15926 Da, molecular weight distribution index (PDI) = 1.35, degree of sulfonation 1.40 mmol / g. Although this product is in the >10000 Da fraction, the molecular weight distribution is still relatively wide, containing a large number of components in the 10000-30000 Da range and some components in the >30000 Da range, failing to achieve a high degree of molecular weight regularization.

[0108] This comparative example demonstrates that single-stage membrane separation cannot achieve the separation effect of the three-stage gradient purification of this invention. The product dispersibility PDI is 1.35, significantly higher than the standard of ≤1.2 for high molecular weight fractions in this invention. This verifies the necessity and inventiveness of the multi-stage gradient ultrafiltration scheme for obtaining products with regular molecular weights.

[0109] Performance testing experiment

[0110] All tests were repeated three times, and the results are expressed as mean ± standard deviation. Formulations were prepared using a uniform wet sand milling process with each dispersant added at a concentration of 3.0%. The results are shown in Tables 1-2.

[0111] Table 1: Core dispersion performance (based on 25% imidacloprid aqueous suspension).

[0112]

[0113] Table 2: Performance comparison of targeted applications.

[0114]

[0115] Analysis of the test results shows that:

[0116] 1. Superior performance in all graded products: The core performance of all graded and refined products of this invention is significantly superior to that of ungraded crude products and commercially available products, especially in terms of suspension rate, particle size distribution and leaf wettability.

[0117] 2. Significant Targeted Application Effects: LS-H exhibits irreplaceable stability in high-solids systems (compared to LS-M), LS-M is highly effective in reducing dynamic surface tension and leaf wetting, and LS-L is key to preparing highly transparent, refined formulations. This confirms the correctness and inventiveness of the "graded-targeted application" strategy of this invention.

[0118] 3. Synergistic effect of compounding: The compounding scheme in Example 4 achieved optimal results in particle size distribution and suspension rate, proving the designability of graded fractionation.

[0119] 4. Necessity of gradient separation: Comparative Example 4 demonstrates that single-stage membrane separation cannot achieve high molecular weight regularization. The three-stage gradient scheme of this invention is the key to obtaining products with PDI < 1.2.

[0120] The following section presents a graded screening verification experiment for Example 1, and compares graded separation and three-level gradient separation between Example 1 and Comparative Example 4.

[0121] First, a graded screening verification experiment.

[0122] To verify the targeting compatibility between different molecular weight fractions and different types of pesticide formulations.

[0123] Three fractions prepared in Example 1—LS-H (high molecular weight fraction), LS-M (medium molecular weight fraction), and LS-L (low molecular weight fraction)—were used to prepare 25% imidacloprid aqueous suspensions at an addition rate of 3.5%. The storage stability (suspension rate after 14 days of heat storage at 54℃) and leaf wettability (static contact angle of cabbage leaves) of each formulation were tested. The results are shown in Table 3.

[0124] Table 3: Results of the grading screening verification test.

[0125]

[0126] Conclusion: LS-H exhibits the best storage stability (93.5% suspension rate) but insufficient wettability (58.2° contact angle); LS-M demonstrates the best wettability (35.5° contact angle) and good stability (91.8% suspension rate); LS-L shows unsatisfactory performance in both aspects. This confirms that different fractions possess different performance advantages and should be selected based on specific dosage form requirements.

[0127] Second, the synergistic effect verification experiment of compound formulation.

[0128] To verify whether the combination of high molecular weight fraction (LS-H) and medium molecular weight fraction (LS-M) produces a synergistic effect.

[0129] With a fixed total addition of 3.5%, different LS-H:LS-M compounding ratios (1:3, 1:2, 1:1, 2:1, 3:1) were set to prepare 25% imidacloprid aqueous suspensions. Various performance indicators were tested and compared with single fractions. The results are shown in Table 4.

[0130] Table 4: Results of the experimental verification of synergistic effect of compound formulation.

[0131]

[0132] Overall score = Suspension rate × 0.5 + (100 - SPAN) × 20 + (90 - Contact angle) × 0.5. The higher the score, the better the overall performance.

[0133] Key findings:

[0134] 1. Particle size optimization: When the compound ratio is 2:1, D50 is reduced to 2.4μm and SPAN is reduced to 1.01, which is significantly better than single fractions;

[0135] 2. Improved suspension rate: When the compound ratio is 2:1, the suspension rate at room temperature reaches 97.8% after 30 days, which is 2 percentage points higher than that of LS-H alone (95.8%) and 1.3 percentage points higher than that of LS-M alone (96.5%), showing a positive synergistic effect;

[0136] 3. Balanced wettability: When the compound ratio is 2:1, the contact angle is 34.8°, which is slightly higher than that of LS-M alone (35.5°), but still much lower than that of LS-H (58.2°). This ensures excellent wettability while maintaining storage stability.

[0137] 4. Determination of the optimal ratio: The comprehensive score shows that LS-H:LS-M=2:1 is the optimal compound ratio, which achieves the best balance between storage stability and leaf wettability.

[0138] Conclusion: The combination of high molecular weight fraction and medium molecular weight fraction can produce synergistic effects. High molecular weight fraction provides strong steric stabilization effect (ensuring storage stability), while medium molecular weight fraction provides excellent surface activity and wetting and spreading properties (ensuring field application effect). The combination of the two in a 2:1 ratio can achieve a comprehensive performance improvement of "1+1>2".

[0139] Third, a comparative verification of single-level separation and three-level gradient separation.

[0140] Verify the necessity of three-stage gradient ultrafiltration for obtaining well-ordered fractions with low dispersion (PDI≤1.2).

[0141] The molecular weight distribution characteristics of the products from the three-stage gradient separation of Example 1 and the products from the single-stage separation (10000 Da membrane only) of Comparative Example 4 were compared. The results are shown in Table 5.

[0142] Table 5: Comparison results of single-level separation and three-level gradient separation.

[0143]

[0144] Conclusion: Single-stage membrane separation cannot achieve highly regularized molecular weight (PDI=1.35), and the product still contains a large number of ultra-large molecular components >30000 Da. The three-stage gradient scheme of this invention is the key technical guarantee for obtaining a regularized product with PDI <1.2.

[0145] Fourth, validation of targeted application of different pesticide formulations.

[0146] Verify the targeting and adaptation effects of each fraction in different pesticide formulations.

[0147] Compatibility tests were conducted using three fractions: LS-H, LS-M, and LS-L, for high-solids-content aqueous suspension (40% chlorothalonil SC), conventional aqueous suspension (25% imidacloprid SC), and soluble concentrate (1% brassinolide SL). The results are shown in Table 6.

[0148] Table 6: Results of targeted application of different pesticide formulations.

[0149]

[0150] Conclusion: Using incorrect fractions in incorrect systems leads to significant performance degradation—high-solids systems must use LS-H (steric hindrance dominant), conventional systems preferably use LS-M (optimal wettability), and soluble agents must use LS-L (solubilizing and dispersing dominant). This fully demonstrates the necessity and innovation of the "fractionation-targeting application" strategy.

[0151] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for the graded purification of straw-based regular molecular weight lignin sulfonate for pesticide dispersants, characterized in that, Includes the following steps: S1. Straw pretreatment and crude lignin extraction: Wheat straw or corn straw is washed, dried, crushed, and sieved to obtain straw powder; the straw powder is mixed with 8%-12% sodium hydroxide solution at a solid-liquid ratio of 1:8-1:12 g / mL, stirred at 80-90℃ for 2-4 hours, filtered to remove residue, and the filtrate is collected; the pH of the filtrate is adjusted to 2.0-3.0, allowed to stand to precipitate, centrifuged, washed, and dried to obtain crude straw lignin; S2. Lignin sulfonation modification: Disperse crude lignin from straw in deionized water to prepare an aqueous suspension with a mass fraction of 15%-25%. Adjust the pH to 10.0-11.0, add 37% formaldehyde solution and sodium sulfite, and reflux at 90-105℃ for 3-5 hours to complete the sulfonation modification. Cool and filter to obtain crude lignin sulfonate mother liquor. S3. Gradient ultrafiltration and purification: The crude lignin sulfonate mother liquor is diluted to a mass fraction of 3%-5%. Under the conditions of temperature 25-35℃ and pressure 0.2-0.4MPa, a multi-stage gradient ultrafiltration membrane is used to perform gradient ultrafiltration circulation filtration in order of molecular weight from large to small, and three groups of lignin sulfonate intercepted liquids with regular molecular weights of large, medium and small are obtained respectively. S4. Post-processing and refining: The three groups of lignin sulfonate intercepting liquids with regular molecular weights are concentrated and spray-dried to obtain high molecular weight lignin sulfonate fractions, medium molecular weight lignin sulfonate fractions, and low molecular weight lignin sulfonate fractions. The high molecular weight fraction of lignin sulfonate is used in pesticide suspensions with a solid content of 40%-50%, the medium molecular weight fraction of lignin sulfonate is used in pesticide suspensions with a solid content of 5%-40%, and the low molecular weight fraction of lignin sulfonate is used in pesticide solubles with a viscosity ≤10 mPa·s.

2. The method according to claim 1, characterized in that, In step S1, the straw is dried at a temperature of 55-65℃ until the moisture content is ≤5%, then crushed and passed through a 40-60 mesh sieve; allowed to stand and settle for 4-6 hours, and centrifuged at a speed of 8000-10000 r / min for 10-15 minutes.

3. The method according to claim 1, characterized in that, In step S2, the mass ratio of lignin, 37% formaldehyde solution, and anhydrous sodium sulfite is 100:8:15-100:12:25; the degree of sulfonation of the crude lignin sulfonate obtained by sulfonation modification is 1.2-2.0 mmol / g.

4. The method according to claim 1, characterized in that, In step S3, the gradient ultrafiltration cycle is repeated 2-3 times. After multi-stage gradient ultrafiltration, the membrane module is rinsed with deionized water to recover the adsorbed effective components, with a total fraction recovery rate ≥90%. The preparation of the three molecular weight regular lignin sulfonate fractions is as follows: S31, High molecular weight fractionation: The mother liquor is retained using a 10000 Da ultrafiltration membrane, and the retained liquor is concentrated to obtain high molecular weight lignin sulfonate with a molecular weight of 10000-30000 Da and a molecular weight distribution coefficient PDI≤1.

2. S32. Preparation of medium molecular weight fraction: A 5000 Da ultrafiltration membrane was used to retain 10000 Da of the ultrafiltration membrane permeate. The retained solution was concentrated to obtain medium molecular weight lignin sulfonate with a molecular weight of 5000-10000 Da and a molecular weight distribution coefficient PDI≤1.

15. S33. Preparation of low molecular weight fractions: A 1000 Da ultrafiltration membrane is used to retain the 5000 Da ultrafiltration membrane permeate. The retained solution is concentrated to obtain low molecular weight lignin sulfonates with a molecular weight of 1000-5000 Da and a molecular weight distribution coefficient (PDI) ≤ 1.

1.

5. A pesticide dispersant composition, characterized in that, It comprises high molecular weight fractional lignin sulfonate and medium molecular weight fractional lignin sulfonate prepared by any one of the methods described in claims 1-4, wherein the mass ratio of the high molecular weight fractional lignin sulfonate to the medium molecular weight fractional lignin sulfonate is 1:2-3:

1.

6. The pesticide dispersant composition according to claim 5, characterized in that, The mass ratio of the high molecular weight fraction of lignin sulfonate to the medium molecular weight fraction of lignin sulfonate is 2:

1.

7. The pesticide dispersant composition according to claim 5, characterized in that, The total amount of straw-based lignin sulfonate added in the pesticide dispersant composition is 2.0%-4.5% of the total mass of the pesticide dispersant.

8. The pesticide dispersant composition according to claim 5, characterized in that, The pesticide dispersant composition is used to prepare aqueous suspensions, wettable powders, water-dispersible granules, or soluble formulations.

9. The pesticide dispersant composition according to claim 5, characterized in that, The high molecular weight fraction of lignin sulfonate and the medium molecular weight fraction of lignin sulfonate work synergistically to exert a steric stabilization effect and improve leaf wetting and adhesion properties, resulting in a median particle size D50 ≤ 3.2 μm, a particle size distribution span SPAN ≤ 1.1, a suspension rate ≥ 94% after 30 days of storage at room temperature, and a static contact angle of the pesticide solution on crop leaves ≤ 40°.

10. The use of a pesticide dispersant composition as described in any one of claims 5-9 in the preparation of pesticide dispersants.

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