Slow-release pesticide granules and preparation method thereof

Abstract

The invention provides slow-release pesticide granules and a preparation method thereof, relates to the field of pesticides, and aims to realize efficient loading and stable slow release of pesticides by optimizing carrier materials and process conditions. The method comprises the following steps: (1) acidifying attapulgite, and modifying with a silane coupling agent and dialdehyde to prepare modified attapulgite; (2) mixing chitosan with the modified attapulgite, and forming composite microspheres through a cross-linking agent and a reduction reaction; (3) loading cypermethrin and imidacloprid in the composite microspheres to form a drug loading core; and (4) coating by adopting polylactic acid and carboxymethyl cellulose to form an interpenetrating network structure, and finally obtaining the slow-release pesticide granules. Experimental results show that the granules can be continuously released within 30 days, conform to a first-level kinetic model and have no burst release phenomenon. The drug loading efficiency is high, the particle size distribution is uniform, and good monodispersity is shown.

Description

Technical Field

[0001] The present invention relates to the field of pesticides, in particular to a slow-release pesticide granule and a preparation method thereof. Background Art

[0002] In the pesticide field, traditional pesticide formulations often suffer from issues such as short duration of efficacy, susceptibility to environmental factors, and potential harm to non-target organisms. To address these issues, slow-release pesticide granules have emerged as a new formulation. These granules slowly release the active ingredient by loading it into a specific carrier material, thereby extending its duration, reducing pesticide dosage, and minimizing environmental pollution. In recent years, advances in materials science and nanotechnology have led to the application of a variety of novel carrier materials and preparation processes in the development of slow-release pesticide granules, offering new ideas and methods for improving pesticide stability and sustained-release performance.

[0003] In the prior art, attapulgite has been widely studied as a pesticide sustained-release carrier material due to its unique microporous structure and large specific surface area. However, unmodified attapulgite still has deficiencies in drug loading efficiency and sustained-release performance. In addition, chitosan, as a natural polymer material, has also been used to prepare sustained-release pesticide granules due to its good biocompatibility and film-forming properties. However, how to further optimize the performance of the carrier material through chemical modification and composite processes to improve the loading efficiency and sustained-release effect of the drug remains the focus and difficulty of current research. In response to the deficiencies in the prior art, the present invention proposes a composite sustained-release pesticide granule based on modified attapulgite and chitosan and a preparation method thereof, aiming to achieve efficient loading and stable sustained-release of pesticides by optimizing material modification and process conditions. Summary of the Invention

[0004] To achieve the above objectives, the present invention is implemented through the following technical solutions: A method for preparing a sustained-release pesticide granule comprises the following steps: S1: The attapulgite was crushed into 200 mesh and immersed in a 1 mol / L hydrochloric acid solution, stirred at 75°C to 80°C for 2 hours, filtered, washed with water until neutral, and dried at 105°C to obtain acidified attapulgite. The acidified attapulgite was dispersed in a toluene solvent, ultrasonically dispersed for 20 to 30 minutes, and an aminosilane coupling agent was slowly added. The mixture was reacted at 70°C to 80°C for 6 to 8 hours. After the reaction was completed, the solvent was filtered off and vacuum dried to obtain silane coupling agent-modified attapulgite. The silane coupling agent-modified attapulgite was dispersed in a dialdehyde solution, stirred at 30°C to 40°C for 3 to 4 hours, filtered, washed with deionized water several times, and vacuum dried to obtain dialdehyde-modified attapulgite. S2: Chitosan was dissolved in acetic acid solution, a cross-linking agent was added, and the mixture was treated with a high-pressure homogenizer at 15,000 psi for three cycles to obtain a chitosan particle suspension. The chitosan particle suspension was mixed with dialdehyde-modified attapulgite, sodium cyanoborohydride solution and a natural cross-linking agent were added, and the pH value was adjusted to 8-10. The mixture was reduced at room temperature for 10-12 hours and spray-dried to obtain composite microspheres. S3: Dissolve cypermethrin and imidacloprid in an acetone-ethanol mixed solvent, mix the acetone-ethanol solution of cypermethrin and imidacloprid with the composite microspheres prepared in S2, evacuate to -0.09 MPa and maintain for 30 minutes, return to normal pressure, and continue immersing for 2 hours, and dry under reduced pressure at 50°C to constant weight to obtain drug-loaded cores; S4: Dissolve polylactic acid and carboxymethyl cellulose in an ethyl acetate aqueous solution, add citric acid as a pH sensitive agent, and stir evenly to obtain a coating solution. Use a bottom spray gun fluidized bed to fluidize the drug-loaded core prepared in S3, control the inlet air temperature to 40°C, the atomization pressure to 0.3 MPa, and the coating weight gain to 15% to 20% to obtain pesticide-coated particles. Place the pesticide-coated particles in a saturated CaCl2 solution and treat them in the solution steam for 30 minutes to induce the carboxymethyl cellulose and polylactic acid to form an interpenetrating network structure. Vacuum drying is used to obtain sustained-release pesticide granules.

[0005] Preferably, the mass parts of the attapulgite, hydrochloric acid solution, toluene solvent, aminosilane coupling agent and dialdehyde solution are 20-30 parts of attapulgite, 150-200 parts of hydrochloric acid solution, 120-150 parts of toluene solvent, 0.2-0.5 parts of aminosilane coupling agent and 100-150 parts of dialdehyde solution.

[0006] Preferably, the mass proportions of the chitosan, acetic acid solution, crosslinking agent, dialdehyde-modified attapulgite, sodium cyanoborohydride solution and natural crosslinking agent are 10-15 parts of chitosan, 90-120 parts of acetic acid solution, 0.5-1 part of crosslinking agent, 0-30 parts of dialdehyde-modified attapulgite, 8-10 parts of sodium cyanoborohydride solution and 5-7 parts of natural crosslinking agent.

[0007] Preferably, the mass proportions of the cypermethrin, imidacloprid, acetone-ethanol mixed solvent and composite microspheres are 10-15 parts of cypermethrin, 5-8 parts of imidacloprid, 100-150 parts of acetone-ethanol mixed solvent and 30-45 parts of composite microspheres.

[0008] Preferably, the mass proportions of the polylactic acid, carboxymethyl cellulose, ethyl acetate aqueous solution, citric acid, and drug-loaded core are 20-30 parts of polylactic acid, 10-15 parts of carboxymethyl cellulose, 80-120 parts of ethyl acetate aqueous solution, 3-8 parts of citric acid, and 40-65 parts of drug-loaded core.

[0009] Preferably, the aminosilane coupling agent is any one of γ-aminopropyltriethoxysilane and γ-aminopropyltrimethoxysilane.

[0010] Preferably, the dialdehyde consists of glyoxal, glutaraldehyde and water, and the mass ratio of glyoxal, glutaraldehyde and water is 1:1:10.

[0011] Preferably, the mass ratio of acetic acid to water in the acetic acid solution is 99:1.

[0012] Preferably, the cross-linking agent is sodium tripolyphosphate.

[0013] Preferably, the concentration of the sodium cyanoborohydride solution is 0.25 mol / L.

[0014] Preferably, the natural cross-linking agent is genipin.

[0015] Preferably, the mass ratio of ethyl acetate to water is 6:4.

[0016] The present invention provides a slow-release pesticide granule and a preparation method thereof. It has the following beneficial effects: By using attapulgite as the basic carrier material and undergoing acidification, silane coupling agent and dialdehyde modification treatment, the specific surface area and adsorption performance of the material are significantly improved, which can achieve the slow release of drug ingredients and effectively reduce the sudden release of pesticides.

[0017] Chitosan was mixed with dialdehyde-modified attapulgite, and a stable network structure was formed through the reduction reaction of the crosslinker sodium tripolyphosphate and the natural crosslinker genipin, thereby improving the drug loading efficiency and ensuring that more cypermethrin and imidacloprid were effectively encapsulated in the composite microspheres.

[0018] A reduction reaction is carried out under alkaline conditions to reduce the aldehyde groups on the surface of the dialdehyde-modified attapulgite to hydroxyl groups, reducing the irritation of the aldehyde groups, improving the safety and stability of the material, and further optimizing the network structure, making the drug release behavior more controllable.

[0019] By dissolving polylactic acid and carboxymethyl cellulose in an ethyl acetate aqueous solution and adding citric acid as a pH-sensitive agent to form a coating solution, the pesticide-coated particles are treated in a saturated CaCl2 solution using fluidized bed coating technology, inducing the carboxymethyl cellulose and polylactic acid to form an interpenetrating network structure, further enhancing the stability and durability of the sustained-release pesticide granules. DETAILED DESCRIPTION

[0020] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0021] Example 1: A method for preparing a sustained-release pesticide granule, comprising the following steps: S1: 22 parts of attapulgite were crushed to 200 mesh size and immersed in 160 parts of a 1 mol / L hydrochloric acid solution. The mixture was stirred at 78°C for 2 hours. After filtration, the mixture was washed with water until neutral and then dried at 105°C to obtain acidified attapulgite. The acidified attapulgite was dispersed in 135 parts of toluene solvent and ultrasonically dispersed for 25 minutes. 0.35 parts of γ-aminopropyltriethoxysilane was slowly added and the mixture was reacted at 75°C for 7 hours. After the reaction, the solvent was filtered and the mixture was vacuum dried to obtain silane coupling agent-modified attapulgite. Next, the silane coupling agent-modified attapulgite was dispersed in 110 parts of a dialdehyde solution and stirred at 32°C for 3.5 hours. After filtration, the mixture was washed with deionized water several times and vacuum dried to obtain dialdehyde-modified attapulgite.

[0022] S2: Dissolve 11 parts chitosan in 100 parts acetic acid solution, add 0.75 parts sodium tripolyphosphate, and process using a high-pressure homogenizer at 15,000 psi for three cycles to obtain a chitosan particle suspension. This chitosan particle suspension was mixed with 32 parts dialdehyde-modified attapulgite, and 8 parts 0.25 mol / L sodium cyanoborohydride solution and 5 parts genipin were added. The pH was adjusted to 9. Reduction reaction was carried out at room temperature for 11 hours, and composite microspheres were obtained by spray drying.

[0023] S3: Dissolve 11 parts of chlorpyrifos and 6 parts of imidacloprid in 120 parts of an acetone-ethanol mixed solvent, then mix this solution with 32 parts of composite microspheres, evacuate to -0.09 MPa and maintain for 30 minutes. After returning to normal pressure, continue immersing for 2 hours, and dry under reduced pressure at 50°C to constant weight to obtain drug-loaded cores.

[0024] S4: Dissolve 22 parts of polylactic acid and 11 parts of carboxymethyl cellulose in 90 parts of ethyl acetate aqueous solution, add 5 parts of citric acid, and stir to obtain a coating solution. Fifty parts of the drug-loaded cores were fluidized-bed coated using a bottom spray gun fluidized bed, controlling the inlet air temperature to 40°C and the atomization pressure to 0.3 MPa, resulting in an 18% weight gain. The pesticide-coated granules were placed in a saturated CaCl2 solution and treated in the solution vapor for 30 minutes to induce the carboxymethyl cellulose and polylactic acid to form an interpenetrating network structure. Vacuum drying was then performed to obtain a sustained-release pesticide granule.

[0025] Example 2: A method for preparing a sustained-release pesticide granule, comprising the following steps: S1: 25 parts of attapulgite were crushed to 200 mesh size and immersed in 170 parts of a 1 mol / L hydrochloric acid solution. The mixture was stirred at 77°C for 2 hours. After filtration, the mixture was washed with water until neutral and then dried at 105°C to obtain acidified attapulgite. The acidified attapulgite was dispersed in 140 parts of toluene solvent and ultrasonically dispersed for 28 minutes. 0.4 parts of γ-aminopropyltrimethoxysilane was slowly added and the mixture was reacted at 78°C for 6.5 hours. After the reaction, the solvent was filtered and the mixture was vacuum dried to obtain silane coupling agent-modified attapulgite. Next, the silane coupling agent-modified attapulgite was dispersed in 120 parts of a dialdehyde solution and stirred at 38°C for 3 hours. After filtration, the mixture was washed with deionized water several times and vacuum dried to obtain dialdehyde-modified attapulgite.

[0026] Step S2: Dissolve 13 parts of chitosan in 115 parts of acetic acid solution, add 0.8 parts of sodium tripolyphosphate, and use a high-pressure homogenizer at 15,000 psi for three cycles to obtain a chitosan particle suspension. This chitosan particle suspension is then mixed with 38 parts of dialdehyde-modified attapulgite. Add 9.5 parts of a 0.25 mol / L sodium cyanoborohydride solution and 5.5 parts of genipin, and adjust the pH to 9. Reduction reaction is carried out at room temperature for 10.5 hours, and the resulting composite microspheres are then spray-dried.

[0027] S3: Dissolve 12 parts of chlorpyrifos and 7.5 parts of imidacloprid in 135 parts of an acetone-ethanol mixed solvent, then mix this solution with 38 parts of composite microspheres, evacuate to -0.09 MPa and maintain for 30 minutes. After returning to normal pressure, continue immersing for 2.5 hours, and dry under reduced pressure at 50°C to constant weight to obtain drug-loaded cores.

[0028] S4: Dissolve 25 parts of polylactic acid and 13 parts of carboxymethyl cellulose in 95 parts of ethyl acetate aqueous solution, add 6 parts of citric acid, and stir to obtain a coating solution. Fluidize and coat 58 drug-loaded cores using a bottom spray gun fluidized bed, controlling the inlet air temperature to 40°C, the atomization pressure to 0.3 MPa, and the coating weight gain to 20%. Place the pesticide-coated granules in a saturated CaCl2 solution and treat them in the solution vapor for 30 minutes to induce the carboxymethyl cellulose and polylactic acid to form an interpenetrating network structure. Vacuum dry to obtain a sustained-release pesticide granule.

[0029] Example 3: A method for preparing a sustained-release pesticide granule, comprising the following steps: S1: 28 parts of attapulgite were crushed to 200 mesh size and immersed in 180 parts of a 1 mol / L hydrochloric acid solution. The mixture was stirred at 76°C for 2 hours. After filtration, the mixture was washed with water until neutral and then dried at 105°C to obtain acidified attapulgite. The acidified attapulgite was dispersed in 145 parts of toluene solvent and ultrasonically dispersed for 22 minutes. 0.45 parts of γ-aminopropyltriethoxysilane were slowly added and the mixture was reacted at 73°C for 6 hours. After the reaction, the solvent was filtered and the mixture was vacuum dried to obtain silane coupling agent-modified attapulgite. Next, the silane coupling agent-modified attapulgite was dispersed in 130 parts of a dialdehyde solution and stirred at 35°C for 3.8 hours. After filtration, the mixture was washed with deionized water several times and vacuum dried to obtain dialdehyde-modified attapulgite.

[0030] S2: Dissolve 14 parts chitosan in 120 parts acetic acid solution, add 1 part sodium tripolyphosphate, and process using a high-pressure homogenizer at 15,000 psi for three cycles to obtain a chitosan particle suspension. This chitosan particle suspension was then mixed with 40 parts dialdehyde-modified attapulgite. Add 10 parts 0.25 mol / L sodium cyanoborohydride solution and 6 parts genipin, and adjust the pH to 9. Reduction reaction was carried out at room temperature for 12 hours, and the resulting composite microspheres were obtained by spray drying.

[0031] S3: Dissolve 13 parts of chlorpyrifos and 7 parts of imidacloprid in 140 parts of an acetone-ethanol mixed solvent, then mix this solution with 40 parts of the composite microspheres, evacuate to -0.09 MPa and maintain for 30 minutes. After returning to normal pressure, continue immersing for 2.8 hours, and dry under reduced pressure at 50°C to constant weight to obtain the drug-loaded core.

[0032] S4: Dissolve 28 parts of polylactic acid and 14 parts of carboxymethyl cellulose in 100 parts of ethyl acetate aqueous solution, add 6 parts of citric acid, and stir to obtain a coating solution. Fluidize and coat 60 drug-loaded cores using a bottom spray gun fluidized bed, controlling the inlet air temperature to 40°C and the atomization pressure to 0.3 MPa, for a coating weight gain of 16%. Place the pesticide-coated granules in a saturated CaCl2 solution and treat them in the solution vapor for 30 minutes to induce the carboxymethyl cellulose and polylactic acid to form an interpenetrating network structure. Vacuum dry the solution to obtain a sustained-release pesticide granule.

[0033] Example 4: A method for preparing a sustained-release pesticide granule, comprising the following steps: S1: 20 parts of attapulgite were crushed to 200 mesh size and immersed in 150 parts of a 1 mol / L hydrochloric acid solution. The mixture was stirred at 79°C for 2 hours. After filtration, the mixture was washed with water until neutral and then dried at 105°C to obtain acidified attapulgite. The acidified attapulgite was dispersed in 125 parts of toluene solvent and ultrasonically dispersed for 20 minutes. 0.3 parts of γ-aminopropyltrimethoxysilane was slowly added and the mixture was reacted at 72°C for 6 hours. After the reaction, the solvent was filtered and the mixture was vacuum dried to obtain silane coupling agent-modified attapulgite. Next, the silane coupling agent-modified attapulgite was dispersed in 100 parts of a dialdehyde solution and stirred at 33°C for 2.5 hours. After filtration, the mixture was washed with deionized water several times and vacuum dried to obtain dialdehyde-modified attapulgite.

[0034] S2: Dissolve 10 parts chitosan in 90 parts acetic acid solution, add 0.7 parts sodium tripolyphosphate, and process using a high-pressure homogenizer at 15,000 psi for three cycles to obtain a chitosan particle suspension. This chitosan particle suspension was mixed with 30 parts dialdehyde-modified attapulgite, and 8 parts 0.25 mol / L sodium cyanoborohydride solution and 4.5 parts genipin were added. The pH was adjusted to 9. Reduction reaction was carried out at room temperature for 10 hours, and composite microspheres were obtained by spray drying.

[0035] S3: Dissolve 10 parts of cypermethrin and 5 parts of imidacloprid in 100 parts of an acetone-ethanol mixed solvent, then mix this solution with 30 parts of composite microspheres, evacuate to -0.09 MPa and maintain for 30 minutes. After returning to normal pressure, continue immersing for 1.5 hours, and dry under reduced pressure at 50°C to constant weight to obtain drug-loaded cores.

[0036] S4: Dissolve 20 parts of polylactic acid and 10 parts of carboxymethyl cellulose in 80 parts of ethyl acetate aqueous solution, add 4 parts of citric acid, and stir to obtain a coating solution. Fluidize and coat 45 drug-loaded cores using a bottom spray gun fluidized bed, controlling the inlet air temperature to 40°C, the atomization pressure to 0.3 MPa, and the coating weight gain to 15%. Place the pesticide-coated granules in a saturated CaCl2 solution and treat them in the solution vapor for 30 minutes to induce the carboxymethyl cellulose and polylactic acid to form an interpenetrating network structure. Vacuum dry to obtain a sustained-release pesticide granule.

[0037] Example 5: A method for preparing a sustained-release pesticide granule, comprising the following steps: S1: 26 parts of attapulgite were crushed to 200 mesh size and immersed in 175 parts of a 1 mol / L hydrochloric acid solution. The mixture was stirred at 78°C for 2 hours. After filtration, the mixture was washed with water until neutral and then dried at 105°C to obtain acidified attapulgite. The acidified attapulgite was dispersed in 138 parts of toluene solvent and ultrasonically dispersed for 24 minutes. 0.42 parts of γ-aminopropyltriethoxysilane were slowly added and the mixture was reacted at 74°C for 7.5 hours. After the reaction, the solvent was filtered and the mixture was vacuum dried to obtain silane coupling agent-modified attapulgite. Next, the silane coupling agent-modified attapulgite was dispersed in 125 parts of a dialdehyde solution and stirred at 37°C for 3.2 hours. After filtration, the mixture was washed with deionized water several times and vacuum dried to obtain dialdehyde-modified attapulgite.

[0038] S2: Dissolve 12.5 parts of chitosan in 110 parts of acetic acid solution, add 0.85 parts of sodium tripolyphosphate, and use a high-pressure homogenizer at 15,000 psi for three cycles to obtain a chitosan particle suspension. This chitosan particle suspension was mixed with 36 parts of dialdehyde-modified attapulgite. Add 9.2 parts of a 0.25 mol / L sodium cyanoborohydride solution and 5.8 parts of genipin, and adjust the pH to 9. Reduction was carried out at room temperature for 11.5 hours, and the resulting composite microspheres were obtained by spray drying.

[0039] S3: Dissolve 12.5 parts of chlorpyrifos and 6.5 parts of imidacloprid in 130 parts of an acetone-ethanol mixed solvent, then mix this solution with 36 parts of composite microspheres, evacuate to -0.09 MPa and maintain for 30 minutes. After returning to normal pressure, continue immersing for 2.2 hours, and dry under reduced pressure at 50°C to constant weight to obtain drug-loaded cores.

[0040] S4: Dissolve 26 parts of polylactic acid and 12.5 parts of carboxymethyl cellulose in 98 parts of ethyl acetate aqueous solution, add 5.5 parts of citric acid, and stir to obtain a coating solution. Fluid-bed coating of 52 drug-loaded cores was performed using a bottom spray gun fluidized bed, controlling the inlet air temperature to 40°C, the atomization pressure to 0.3 MPa, and the coating weight gain to 17%. The pesticide-coated granules were placed in a saturated CaCl2 solution and treated in the solution vapor for 30 minutes to induce the carboxymethyl cellulose and polylactic acid to form an interpenetrating network structure. The granules were then vacuum-dried to obtain a sustained-release pesticide granule.

[0041] It should be noted that attapulgite, as a basic carrier material, has a microporous structure, a large specific surface area and adsorption properties, can load drug ingredients, and play a sustained-release role. Acidification treatment of attapulgite can remove impurities on the surface of the attapulgite and increase the active sites on its surface, creating conditions for subsequent cross-linking reactions with silane coupling agents and dialdehydes.

[0042] It should be noted that the aminosilane coupling agent, as a bridge molecule, reacts with the hydroxyl groups on the surface of the attapulgite. Through hydrolysis and condensation reactions, the aminosilane coupling agent is firmly connected to the surface of the attapulgite. The dialdehyde solution further reacts with the attapulgite modified with the silane coupling agent, introducing aldehyde functional groups to react with amino or hydroxyl groups on the surface of the attapulgite to form covalent bonds, thereby preparing dialdehyde-modified attapulgite. This further expands the network structure of the attapulgite, increases the cross-linking density of the material, and facilitates the slow release of drugs.

[0043] It should be noted that chitosan is a natural polymer material with good biocompatibility and film-forming properties, and can form a granular structure; the reason for adding acetic acid solution is that under acidic conditions, the hydrogen bonding effect between chitosan chain segments is weakened, which is conducive to the formation of a more uniform suspension.

[0044] It should be noted that after the dialdehyde-modified attapulgite is mixed with the chitosan particle suspension, the aldehyde groups on its surface react with the amino groups on the chitosan molecules, further strengthening the cross-linking degree of the composite material and improving the stability of the material and the drug release performance.

[0045] It should be noted that the cross-linking agent sodium tripolyphosphate forms covalent bonds by chemically reacting with amino or hydroxyl groups on chitosan molecules, connecting the chitosan molecules to form a network structure, which gives the chitosan particles a certain elasticity and strength, and can better load and protect pesticides.

[0046] It should be noted that, as a reducing agent, the aldehyde groups on the surface of the dialdehyde-modified attapulgite are reduced to hydroxyl groups under alkaline conditions, while the cross-linking reaction between chitosan and other components is made more stable. Through the reduction reaction, the formation of chemical bonds is made more stable, the irritation of the aldehyde groups is reduced, the safety and stability of the material are improved, and the network structure is further optimized, making the drug release behavior more controllable.

[0047] It should be noted that the drug-loaded core acts as a drug carrier, encapsulating cypermethrin and imidacloprid, protecting the drugs from the external environment while achieving sustained release. The composite microspheres are a mixture of dialdehyde-modified attapulgite prepared in step S1 and chitosan particles prepared in step S2. They exhibit excellent adsorption and sustained-release properties. The internal reticular structure of the composite microspheres can adsorb and immobilize the pesticides. Upon release of the pesticides, the drugs are slowly released through diffusion and other methods, achieving sustained release.

[0048] Comparative Example 1: A method for preparing a sustained-release pesticide granule, comprising the following steps: S1: Grind 22 parts of attapulgite to 200 mesh size, immerse in 160 parts of 1 mol / L hydrochloric acid solution, and stir at 78°C for 2 hours. Filter, wash with water until neutral, and then dry at 105°C to obtain acidified attapulgite. Disperse the acidified attapulgite in 135 parts of toluene solvent and ultrasonically disperse for 25 minutes. Slowly add 0.35 parts of γ-aminopropyltriethoxysilane and react at 75°C for 7 hours. After the reaction, filter to remove the solvent and vacuum dry to obtain the silane coupling agent-modified attapulgite.

[0049] S2: Dissolve 11 parts chitosan in 100 parts acetic acid solution, add 0.75 parts sodium tripolyphosphate, and use a high-pressure homogenizer at 15,000 psi for three cycles to obtain a chitosan particle suspension. This chitosan particle suspension is then mixed with 32 parts attapulgite modified with a silane coupling agent. Add 8 parts of a 0.25 mol / L sodium cyanoborohydride solution and 5 parts of genipin, and adjust the pH to 9. Reduction reaction is carried out at room temperature for 11 hours, and the resulting composite microspheres are obtained by spray drying.

[0050] S3: Dissolve 11 parts of chlorpyrifos and 6 parts of imidacloprid in 120 parts of an acetone-ethanol mixed solvent, then mix this solution with 32 parts of composite microspheres, evacuate to -0.09 MPa and maintain for 30 minutes. After returning to normal pressure, continue immersing for 2 hours, and dry under reduced pressure at 50°C to constant weight to obtain drug-loaded cores.

[0051] S4: Dissolve 22 parts of polylactic acid and 11 parts of carboxymethyl cellulose in 90 parts of ethyl acetate aqueous solution, add 5 parts of citric acid, and stir to obtain a coating solution. Fifty parts of the drug-loaded cores were fluidized-bed coated using a bottom spray gun fluidized bed, controlling the inlet air temperature to 40°C and the atomization pressure to 0.3 MPa, resulting in an 18% weight gain. The pesticide-coated granules were placed in a saturated CaCl2 solution and treated in the solution vapor for 30 minutes to induce the carboxymethyl cellulose and polylactic acid to form an interpenetrating network structure. Vacuum drying was then performed to obtain a sustained-release pesticide granule.

[0052] Comparative Example 2: A method for preparing a sustained-release pesticide granule, comprising the following steps: S1: 22 parts of attapulgite were crushed to 200 mesh size and immersed in 160 parts of a 1 mol / L hydrochloric acid solution. The mixture was stirred at 78°C for 2 hours. After filtration, the mixture was washed with water until neutral and then dried at 105°C to obtain acidified attapulgite. The acidified attapulgite was dispersed in 135 parts of toluene solvent and ultrasonically dispersed for 25 minutes. 0.35 parts of γ-aminopropyltriethoxysilane was slowly added and the mixture was reacted at 75°C for 7 hours. After the reaction, the solvent was filtered and the mixture was vacuum dried to obtain silane coupling agent-modified attapulgite. Next, the silane coupling agent-modified attapulgite was dispersed in 110 parts of a dialdehyde solution and stirred at 32°C for 3.5 hours. After filtration, the mixture was washed with deionized water several times and vacuum dried to obtain dialdehyde-modified attapulgite.

[0053] S2: Dissolve 11 parts chitosan in 100 parts acetic acid solution, add 0.75 parts sodium tripolyphosphate, and process using a high-pressure homogenizer at 15,000 psi for three cycles to obtain a chitosan particle suspension. This chitosan particle suspension was then mixed with 32 parts dialdehyde-modified attapulgite, and 5 parts genipin was added. The pH was adjusted to 9. Reduction reaction was carried out at room temperature for 11 hours, and the resulting composite microspheres were obtained by spray drying.

[0054] S3: Dissolve 11 parts of chlorpyrifos and 6 parts of imidacloprid in 120 parts of an acetone-ethanol mixed solvent, then mix this solution with 32 parts of composite microspheres, evacuate to -0.09 MPa and maintain for 30 minutes. After returning to normal pressure, continue immersing for 2 hours, and dry under reduced pressure at 50°C to constant weight to obtain drug-loaded cores.

[0055] S4: Dissolve 22 parts of polylactic acid and 11 parts of carboxymethyl cellulose in 90 parts of ethyl acetate aqueous solution, add 5 parts of citric acid, and stir to obtain a coating solution. Fifty parts of the drug-loaded cores were fluidized-bed coated using a bottom spray gun fluidized bed, controlling the inlet air temperature to 40°C and the atomization pressure to 0.3 MPa, resulting in an 18% weight gain. The pesticide-coated granules were placed in a saturated CaCl2 solution and treated in the solution vapor for 30 minutes to induce the carboxymethyl cellulose and polylactic acid to form an interpenetrating network structure. Vacuum drying was then performed to obtain a sustained-release pesticide granule.

[0056] Experimental methods: Sustained-release performance test: 1.0 g of the sustained-release pesticide granules prepared in Example 1 was weighed and placed in 500 mL of deionized water, maintained at a constant temperature of 25°C. 5 mL of the solution was collected every 24 hours and filtered through a 0.22 μm filter membrane. The release of cypermethrin and imidacloprid was determined by high-performance liquid chromatography (HPLC). The cumulative release rate was calculated based on the standard curve, and a sustained-release curve was plotted over 30 days. Detailed results are shown in Table 1.

[0057] Drug loading efficiency determination: 100 mg of the sustained-release pesticide granules prepared in Examples 1 to 5 and Comparative Examples 1 to 2 were ground and dissolved in 10 mL of an acetone-ethanol mixed solvent. The mixture was ultrasonically treated for 30 minutes to completely release the drug. The total amount of cypermethrin and imidacloprid in the solution was determined by HPLC, and the loading efficiency was calculated: , detailed results are shown in Table 2.

[0058] Particle size distribution (DLS): The granules prepared in Examples 1 to 5 and Comparative Examples 1 to 2 were dispersed in deionized water and ultrasonically dispersed for 10 minutes. The particle size distribution was measured using a dynamic light scattering instrument (Malvern Zetasizer Nano ZS). Detailed results are shown in Table 3.

[0059] Table 1

[0060] Conclusion: The granules achieved sustained release over 30 days, which was consistent with the first-order kinetic model (R² > 0.98) and without burst release.

[0061] Table 2

[0062] Table 3

[0063] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the equivalents of the appended claims.

Claims

1. A method for preparing a sustained-release pesticide granule, characterized in that: The steps include: S1: crushing attapulgite and adding it to a hydrochloric acid solution and stirring, filtering, washing with water until neutral and drying to obtain acidified attapulgite, dispersing the acidified attapulgite in a toluene solvent, slowly adding an aminosilane coupling agent and heating to react, filtering to remove the solvent, and vacuum drying to obtain silane coupling agent-modified attapulgite, dispersing the silane coupling agent-modified attapulgite in a dialdehyde solution, heating and stirring, filtering, washing with deionized water several times, and vacuum drying to obtain dialdehyde-modified attapulgite; S2: Dissolve chitosan in acetic acid solution, add a cross-linking agent, and process with a high-pressure homogenizer to obtain a chitosan particle suspension. Mix the chitosan particle suspension with modified attapulgite clay rods, add sodium cyanoborohydride solution and a natural cross-linking agent, adjust the pH to weak alkaline, carry out a reduction reaction at room temperature, and spray dry to obtain composite microspheres. S3: dissolving cypermethrin and imidacloprid in an acetone-ethanol mixed solvent, mixing the acetone-ethanol solution of cypermethrin and imidacloprid with the composite microspheres prepared in S2, evacuating the mixture and maintaining the mixture for a certain period of time, then returning the mixture to normal pressure and continuing the immersion, and then drying the mixture under reduced pressure to a constant weight to obtain drug-loaded cores; S4: Dissolve polylactic acid and carboxymethyl cellulose in an ethyl acetate aqueous solution, add citric acid as a pH sensitive agent, and stir evenly to obtain a coating solution. Use a bottom spray gun fluidized bed to fluidize the drug-loaded core prepared in S3 to obtain pesticide-coated particles. Place the pesticide-coated particles in a saturated CaCl2 solution, treat them in steam, and vacuum dry them to obtain sustained-release pesticide granules.

2. The method for preparing a sustained-release pesticide granule according to claim 1, characterized in that: In S1, attapulgite is crushed to 200 mesh and then immersed in 1 mol / L hydrochloric acid solution, stirred at 75°C to 80°C for 2 hours, and then dried at 105°C. After slowly adding the aminosilane coupling agent, react at 70°C to 80°C for 6 to 8 hours; The solid-liquid mass ratio of the silane coupling agent modified attapulgite to the dialdehyde solution is 1:10-1:15, and the mixture is stirred at 30° C.-40° C. for 3-4 hours.

3. The method for preparing a sustained-release pesticide granule according to claim 1, characterized in that: In S2, the high-pressure homogenizer was used for 3 cycles at 15,000 psi, with a vacuum degree of -0.09 MPa, and the process was maintained for 30 minutes; In the fluidized bed coating of S4, the inlet air temperature is controlled at 40°C and the atomization pressure is 0.3 MPa, which makes the coating weight increase by 15% to 20%.

4. The method for preparing a sustained-release pesticide granule according to claim 1, characterized in that: The aminosilane coupling agent is any one of γ-aminopropyltriethoxysilane and γ-aminopropyltrimethoxysilane, the dialdehyde is composed of glyoxal, glutaraldehyde and water, the mass ratio of glyoxal, glutaraldehyde and water is 1:1:10, and the mass ratio of acetic acid to water in the acetic acid solution is 99:

1.

5. The method for preparing a sustained-release pesticide granule according to claim 1, characterized in that: The cross-linking agent is sodium tripolyphosphate.

6. The method for preparing a sustained-release pesticide granule according to claim 1, characterized in that: The concentration of the sodium cyanoborohydride solution is 0.25 mol / L.

7. The method for preparing a sustained-release pesticide granule according to claim 1, characterized in that: The natural cross-linking agent is genipin.

8. The method for preparing a sustained-release pesticide granule according to claim 1, characterized in that: The mass ratio of the ethyl acetate to water is 6:

4.

9. A sustained-release pesticide granule, characterized in that: The sustained-release pesticide granules are obtained by the preparation method of any one of claims 1 to 8.

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