A pH-responsive pesticide slow-release hydrogel sphere and its preparation method

Abstract

The present invention discloses a pH-responsive pesticide slow-release hydrogel sphere and a preparation method thereof, belonging to the technical field of slow-release pesticides. The present invention uses carboxylated nanocrystalline cellulose modified by polyethyleneimine as a raw material, which is self-assembled with modified montmorillonite through electrostatic binding, and then loaded with pesticides in an organic solvent. Then, sodium alginate is used as a coating material and anhydrous calcium chloride is used as a cross-linking agent to prepare a pH-responsive pesticide slow-release hydrogel sphere of nanocrystalline cellulose composite montmorillonite by dropping, which is used for the slow release of pesticides in the soil environment. Under the optimal conditions, the encapsulation rate of fipronil in the organic solvent by the hydrogel sphere of the present invention is above 64.1 wt%, and the loading rate is above 67.3 wt%. In the soil environment with different pH values, the highest release rate of pesticides after 120 h is above 59.7%, and the pesticide release rate increases with the increase of pH until the hydrogel skeleton completely breaks, and the purpose of adjusting the pesticide release rate can be achieved by adjusting the pH.

Description

Technical Field

[0001] The present invention belongs to the technical field of slow-release pesticides, and particularly relates to a pH-responsive pesticide slow-release hydrogel sphere and a preparation method thereof. Background Art

[0002] Pesticides refer to chemical agents used in agriculture to control pests and diseases and regulate plant growth, and are widely used in the production of agriculture, forestry and animal husbandry, environmental and household sanitation pest control and epidemic prevention, anti-mildew and anti-moth of industrial products, etc. Traditional pesticide formulations are mainly emulsifiable concentrates and wettable powders. These formulations are restricted by external factors such as soil erosion, high-temperature evaporation, and drug decomposition, resulting in a pesticide utilization rate of less than 30 wt%. This not only causes waste of excessive pesticide application but also exerts great pressure on the environment of agricultural land.

[0003] Hydrogel, as a hydrophilic three-dimensional structure, consists of two phases: a polymer phase and an aqueous phase, and has strong water absorption and water retention capabilities. Using hydrogel as a pesticide release device has many advantages. For example, the hydrogel can automatically release the drug to the target location at a slow speed within a specified time, thereby demonstrating specificity. In addition, the hydrogel can maximize the efficacy of pesticides and reduce unnecessary losses. Hydrogels are divided into vinyl and natural polymer-based hydrogels. Most commercial products are based on polyacrylamide and acrylate derivatives, which not only have high production costs but also cannot be biodegradable, so they are considered potential environmental pollutants. In contrast, natural polymer materials have the advantages of biodegradability, economic availability, good biocompatibility, and renewability, and are therefore widely used in hydrogel drug delivery systems. In the existing literature, sodium carboxymethyl cellulose (CMC-Na) and hydroxyethyl cellulose (HEC)-based biodegradable hydrogels have been prepared, and their swelling ability has reached 600%, improving the utilization rate of agricultural water.

[0004] Although the hydrogel formed by monomer polymerization has excellent water retention performance, it also has structural defects. When the hydrogel is subjected to external forces, the hydrogel structure is prone to breakage and fracture, which will affect the mechanical properties and stability of the network structure to a certain extent and reduce its use value. The hydrogel composed of multiple substances can form a variety of intermolecular forces, which not only improves the mechanical properties and stability of the hydrogel, but also endows the hydrogel with special properties such as self-healing and responsiveness. A large number of studies have found that the addition of nanomaterials can improve the mechanical properties of hydrogels. In the existing literature, hydrogels based on sodium alginate, polyvinyl acetate and nanocellulose have been prepared to control the release of nitrogen, phosphorus and potassium fertilizers into water bodies and soils. Another literature shows that nanocellulose improves the biodegradability of poly(3-hydroxybutyrate) / starch-based composites through potassium nitrate microspheres. The common methods for compounding nanocellulose with materials mainly include: blending, coating, deposition or doping, etc. Although the methods are simple and easy to implement, the materials are only physically mixed, which easily leads to agglomeration and accumulation of nanomaterials, poor uniformity, and it is difficult to effectively improve the performance of nanocomposite functional materials.

[0005] Self-assembly refers to a technique in which basic structural units (molecules, nanomaterials, substances at the micron or larger scale) spontaneously form an ordered structure. During the self-assembly process, the basic structural units spontaneously organize or aggregate into a stable structure with a certain regular geometric appearance based on non-covalent interactions. The operation of the self-assembly technique is simple and fast. It can not only effectively control the microscopic morphology of nanocomposite functional materials, obtain a dense hierarchical structure, but also effectively improve the mechanical properties of its own structure.

[0006] Based on the above, the present invention provides a method for preparing a nanocellulose crystal-based pesticide slow-release hydrogel sphere. Carboxylated nanocellulose crystals are modified by polyethyleneimine, and acidified montmorillonite is prepared using hydrochloric acid solution. After self-assembly through electrostatic binding, pesticides are loaded in an organic solvent using the assembly, sodium alginate is used as a coating material, and anhydrous calcium chloride is used as a cross-linking agent. A pH-responsive hydrogel sphere of nanocellulose crystal composite montmorillonite is prepared by dropping. Summary of the Invention

[0007] To solve the above technical problems, the present invention provides a pH-responsive pesticide slow-release hydrogel sphere and a preparation method thereof. By preparing an organic-inorganic composite hydrogel, its mechanical properties and loading capacity are improved, and the hydrogel is endowed with pH responsiveness to improve its use value.

[0008] The present invention is achieved through the following technical solutions:

[0009] A method for preparing a pH-responsive pesticide slow-release hydrogel sphere, comprising the following steps:

[0010] (1) Preparation of polyethyleneimine-modified nanocrystalline cellulose: Take an aqueous solution of polyethyleneimine and add it to a suspension of carboxylated nanocrystalline cellulose. Continuously stir, adjust the pH of the resulting mixed solution with an acid, continue stirring, centrifuge, wash the resulting precipitate, and freeze-dry to obtain polyethyleneimine-modified nanocrystalline cellulose powder;

[0011] (2) Preparation and pretreatment of montmorillonite: Add a dispersant to a bentonite slurry, stir, let it stand for sedimentation, centrifuge, dry the resulting supernatant, grind it, and sieve it. Disperse the resulting montmorillonite in an HCl solution, stir, wash, filter, dry, and grind it to obtain pretreated montmorillonite powder;

[0012] (3) Preparation of the assembly: Disperse the pretreated montmorillonite powder and the polyethyleneimine-modified nanocrystalline cellulose powder in water respectively to obtain a pretreated montmorillonite suspension and a polyethyleneimine-modified nanocrystalline cellulose suspension; Dropwise add the resulting pretreated montmorillonite suspension to the resulting polyethyleneimine-modified nanocrystalline cellulose suspension, continuously stir to obtain an assembly suspension, and freeze-dry to obtain assembly powder;

[0013] (4) Preparation of pH-responsive pesticide slow-release hydrogel beads: Disperse the assembly powder in a pesticide solution, after shaking, centrifuging, washing, and drying, disperse the resulting pesticide-loaded assembly powder in water, add sodium alginate, and dropwise add it to a CaCl2 solution under stirring conditions, let it stand, wash, and vacuum-dry to obtain pH-responsive pesticide slow-release hydrogel beads.

[0014] Further, in step (4), the mass ratio of the pesticide-loaded assembly powder to sodium alginate is 1:0.5 - 1.

[0015] Further, in step (4), the mass-to-volume ratio of the assembly powder to the pesticide is 1 g:200 - 250 mL; the pesticide is fipronil, and the concentration of fipronil is 10 - 20 mg / mL.

[0016] Further, in step (3), the mass ratio of the pretreated montmorillonite and the polyethyleneimine-modified nanocrystalline cellulose contained in the assembly powder is 1:1 - 5.

[0017] Further, in step (3), the mass fraction of the pretreated montmorillonite suspension is 0.2 - 0.5 wt%, and the mass fraction of the polyethyleneimine-modified nanocrystalline cellulose suspension is 0.8 - 1 wt%.

[0018] Further, in step (2), the dispersant is any one or a combination of two or more of sodium hexametaphosphate, sodium pyrophosphate, and sodium silicate.

[0019] Further, in step (2), the solid-liquid mass ratio of the bentonite slurry is 10-12:1.

[0020] Further, in step (1), the mass fraction of the polyethyleneimine aqueous solution is 1-5 wt%, and the mass fraction of the carboxylated nanocellulose crystal suspension is 1-5 wt%.

[0021] Further, in step (1), the carboxylated nanocellulose crystal has a diameter of 4-10 nm, a length of 100-500 nm, and a surface carboxyl content of 1.8-2 mmol / g

[0022] Further, in step (1), the pH value of the mixed solution is adjusted to 1-3 with concentrated hydrochloric acid.

[0023] A pH-responsive pesticide slow-release hydrogel ball prepared by the method for preparing a pH-responsive pesticide slow-release hydrogel ball as described above.

[0024] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0025] 1. The present invention prepares an organic-inorganic composite hydrogel to improve its mechanical properties and loading capacity, and endows the hydrogel with pH responsiveness to improve its use value. The present invention uses carboxylated nanocellulose crystals modified with polyethyleneimine as raw materials, and self-assembles with modified montmorillonite through electrostatic binding. Sodium alginate is used as the coating material and anhydrous calcium chloride is used as the cross-linking agent. A pH-responsive pesticide slow-release hydrogel ball of nanocellulose crystal composite montmorillonite is prepared by dropping. This method has simple process, low energy consumption, simple equipment, and the raw materials have good biocompatibility and biodegradability. The prepared pH-responsive pesticide slow-release hydrogel ball has a good pesticide controlled-release effect.

[0026] 2. The present invention modifies carboxylated nanocellulose crystals with polyethyleneimine and uses hydrochloric acid solution to prepare acidified montmorillonite, making the two have opposite charges and similar absolute values of potential, which is more conducive to binding through electrostatic force. The nanocellulose crystals adhere to the surface of the layered nanomontmorillonite sheets. The binding process can be carried out in an aqueous solution at room temperature, with a simple process and low energy consumption. At the same time, this method also solves the problems of agglomeration and poor order of nanomaterials in common mixing methods. The operation of the self-assembly technology is simple and fast. It can not only effectively control the microscopic morphology of the nanocomposite functional materials and obtain a dense hierarchical structure, but also maintain the structure and morphology of the nanomaterials themselves.

[0027] 3. The present invention uses sodium alginate as the network material of the hydrogel, and adds nanocellulose to the sodium alginate hydrogel network, which can overcome the limitations of large surface pores, poor mechanical strength, and easy "burst release" of drugs in sodium alginate hydrogels. At the same time, the crystals of nanocellulose crystals can improve the mechanical properties of the hydrogel, prevent its structure from being damaged and fractured when subjected to external forces, and reduce its use value.

[0028] 4. The present invention utilizes the natural activity and low cost of bentonite, a rich mineral resource in Guangxi, purifies montmorillonite and acidifies it, which can weaken the intermolecular force between montmorillonite layers, increase the absolute value of the permanent negative charge carried by montmorillonite, and is more conducive to the subsequent assembly process. In addition, the metal material cations between layers are replaced, the pore volume and specific surface area are greatly increased, the adsorption sites are also increased to a certain extent, and the adsorption working ability is improved, which is conducive to the subsequent loading of pesticide molecules.

[0029] 5. Under the optimal conditions, the encapsulation rate of the hydrogel beads of the present invention for fipronil in organic solvents is above 64.1 wt%, the loading rate is above 67.3 wt%. In soil environments with different pH values, the highest release rate of pesticides after 120 h is above 59.7%, and the pesticide release rate increases with the increase of pH until the hydrogel skeleton completely breaks, indicating that the hydrogel beads of the present invention can achieve the purpose of adjusting the pesticide release rate by adjusting the pH. Description of the Drawings

[0030] Figure 1 It is the nitrogen adsorption-desorption curve diagram of bentonite, montmorillonite and acidified montmorillonite in Example 1.

[0031] Figure 2 It is the ultraviolet spectrogram of pesticides in the pH-responsive nanocellulose crystal-based hydrogel beads in Example 1 over time.

[0032] Figure 3 It is the release rate curve diagram of the pH-responsive nanocellulose crystal-based hydrogel beads in Example 1 under different pH conditions within 120 h. Detailed Embodiments

[0033] The following further elaborates on the present invention through examples, and these examples are only used to illustrate the present invention and do not limit the protection scope of the present invention.

[0034] Example 1

[0035] (1) Preparation of polyethyleneimine-modified nanocrystalline cellulose: Add 3 wt% aqueous polyethyleneimine solution to 3 wt% carboxylated nanocrystalline cellulose suspension. The diameter of the nanocrystalline cellulose is 4 - 10 nm, the length is 100 - 500 nm, and the surface carboxyl content is 1.9 mmol / g. Continuously stir at room temperature for 1 h, then adjust the pH of the mixed solution to 2 with concentrated hydrochloric acid, continue stirring for 10 min, then centrifuge the mixed solution at high speed, discard the supernatant, wash the precipitate three times and then perform freeze-drying to obtain polyethyleneimine-modified nanocrystalline cellulose powder;

[0036] (2) Preparation and pretreatment of montmorillonite: Prepare a bentonite slurry with a solid-liquid mass ratio of 12:1, use sodium hexametaphosphate as a dispersant, the pH of the solution is 9, stir at room temperature for 80 min, let it stand and settle, remove the slag, take the supernatant after low-speed centrifugation for 5 min, dry at 105 °C, grind, and pass through a 200-mesh sieve to obtain montmorillonite. Weigh 10 g of montmorillonite and disperse it in HCl solution, stir magnetically at room temperature for 4 h, wash with water until neutral and then filter, dry in an oven at 60 °C, then grind to obtain the pretreated montmorillonite powder, pack it and set aside;

[0037] (3) Preparation of the assembly: Disperse the pretreated montmorillonite powder and the polyethyleneimine-modified nanocrystalline cellulose powder in water respectively to obtain a 0.2 wt% pretreated montmorillonite suspension and a 1.0 wt% polyethyleneimine-modified nanocrystalline cellulose suspension. Dropwise add the pretreated montmorillonite suspension into the polyethyleneimine-modified nanocrystalline cellulose suspension, continuously stir for 24 h to obtain an assembly suspension, and after freeze-drying, obtain an assembly powder with a mass ratio of pretreated montmorillonite to polyethyleneimine-modified nanocrystalline cellulose of 1:5;

[0038] (4) Preparation of pH-responsive pesticide slow-release hydrogel beads: Weigh 1 g of the assembly powder, disperse it in 200 mL of fipronil ethanol solution with a concentration of 15 mg / mL, oscillate at room temperature for 12 h, then centrifuge, wash twice with a small amount of ethanol and dry at 60 °C to obtain the fipronil-loaded assembly powder. Take 1 g of the fipronil-loaded assembly powder and disperse it in 30 mL of deionized water, add 0.5 g of sodium alginate, and use a dropper to drop it into 400 mL of CaCl2 solution with a concentration of 0.4 mol / L under stirring conditions. After dropping, keep it in the CaCl2 solution for 30 min, wash three times and dry under vacuum to obtain pH-responsive nanocrystalline cellulose-based hydrogel beads.

[0039] Example 2

[0040] (1) Preparation of polyethyleneimine-modified nanocrystalline cellulose: Add 2 wt% aqueous solution of polyethyleneimine to 2 wt% carboxylated nanocrystalline cellulose suspension. The diameter of nanocrystalline cellulose is 4 - 10 nm, the length is 100 - 500 nm, and the surface carboxyl content is 1.9 mmol / g. Continuously stir at room temperature for 1 h, then adjust the pH of the mixed solution to 2 with concentrated hydrochloric acid, continue to stir for 10 min, then centrifuge the mixed solution at high speed, discard the supernatant, wash the precipitate three times and then perform freeze-drying to obtain polyethyleneimine-modified nanocrystalline cellulose powder;

[0041] (2) Preparation and pretreatment of montmorillonite: Prepare a bentonite slurry with a solid-liquid mass ratio of 10:1, use sodium pyrophosphate as a dispersant, the pH of the solution is 8, stir at room temperature for 80 min, let it stand and settle, remove the residue, take the supernatant after low-speed centrifugation for 5 min, dry at 105 °C, grind, and pass through a 200-mesh sieve to obtain montmorillonite. Weigh 4 g of montmorillonite and disperse it in HCl solution, stir magnetically at room temperature for 4 h, wash with water until neutral, then filter, dry in an oven at 60 °C, and then grind to obtain the pretreated montmorillonite powder, which is bagged and reserved;

[0042] (3) Preparation of the assembly: Disperse the pretreated montmorillonite powder and polyethyleneimine-modified nanocrystalline cellulose powder in water respectively to obtain a 0.3 wt% pretreated montmorillonite suspension and a 1.0 wt% polyethyleneimine-modified nanocrystalline cellulose suspension. Dropwise add the pretreated montmorillonite suspension into the polyethyleneimine-modified nanocrystalline cellulose suspension, continuously stir for 24 h to obtain an assembly suspension, and after freeze-drying, obtain an assembly powder with a mass ratio of pretreated montmorillonite to polyethyleneimine-modified nanocrystalline cellulose of 1:1;

[0043] (4) Preparation of pH-responsive pesticide slow-release hydrogel beads: Weigh 1 g of the assembly powder, disperse it in 200 mL of fipronil ethanol solution with a concentration of 15 mg / mL, oscillate at room temperature for 12 h, then centrifuge, wash twice with a small amount of ethanol, and dry at 60 °C to obtain the fipronil-loaded assembly powder. Take 1 g of the fipronil-loaded assembly powder and disperse it in 30 mL of deionized water, add 0.8 g of sodium alginate, and use a dropper to drop it into 400 mL of CaCl2 solution with a concentration of 0.4 mol / L under stirring conditions. After dropping, keep it in the CaCl2 solution for 30 min, wash three times and dry in vacuum to obtain pH-responsive nanocrystalline cellulose-based hydrogel beads.

[0044] Example 3

[0045] (1) Preparation of polyethyleneimine-modified nanocrystalline cellulose: Add 2 wt% aqueous solution of polyethyleneimine to 2 wt% suspension of carboxylated nanocrystalline cellulose, and continuously stir at room temperature for 1 h. The diameter of the nanocrystalline cellulose is 4 - 10 nm, the length is 100 - 500 nm, and the surface carboxyl content is 1.9 mmol / g. Then, adjust the pH of the mixed solution to 2 with concentrated hydrochloric acid, continue stirring for 10 min, and then centrifuge the mixed solution at high speed. Discard the supernatant, wash the precipitate three times, and then perform freeze-drying to obtain polyethyleneimine-modified nanocrystalline cellulose powder;

[0046] (2) Preparation and pretreatment of montmorillonite: Prepare a bentonite slurry with a solid-liquid mass ratio of 11:1, use sodium silicate as a dispersant, the pH of the solution is 9, stir at room temperature for 80 min, let it stand for sedimentation, remove the slag, centrifuge at low speed for 5 min, and take the supernatant. Dry it at 105 °C, grind it, and pass it through a 200-mesh sieve to obtain montmorillonite. Weigh 2 g of montmorillonite and disperse it in an HC1 solution, stir magnetically at room temperature for 8 h, wash it with water until neutral, filter it, dry it in an oven at 60 °C, and then grind it to obtain the pretreated montmorillonite powder, which is bagged and reserved;

[0047] (3) Preparation of the assembly: Disperse the pretreated montmorillonite powder and polyethyleneimine-modified nanocrystalline cellulose powder in water respectively to obtain a 0.4 wt% suspension of pretreated montmorillonite and a 1.0 wt% suspension of polyethyleneimine-modified nanocrystalline cellulose. Dropwise add the pretreated montmorillonite suspension into the polyethyleneimine-modified nanocrystalline cellulose suspension, and continuously stir for 24 h to obtain an assembly suspension. After freeze-drying, an assembly powder with a mass ratio of pretreated montmorillonite to polyethyleneimine-modified nanocrystalline cellulose of 2:5 is obtained;

[0048] (4) Preparation of pH-responsive pesticide slow-release hydrogel beads: Weigh 1 g of the assembly powder, disperse it in 200 mL of fipronil ethanol solution with a concentration of 15 mg / mL, oscillate at room temperature for 12 h, then centrifuge, wash it twice with a small amount of ethanol, and dry it at 60 °C to obtain fipronil-loaded assembly powder. Take 1 g of the fipronil-loaded assembly powder and disperse it in 30 mL of deionized water, add 0.6 g of sodium alginate, and use a dropper to drop it into 400 mL of CaCl2 solution with a concentration of 0.4 mol / L under stirring conditions. After dropping, keep it in the CaCl2 solution for 30 min, wash it three times and dry it under vacuum to obtain pH-responsive nanocrystalline cellulose-based hydrogel beads.

[0049] Material property testing

[0050] 1. Perform nitrogen adsorption-desorption tests and analyses on the bentonite, montmorillonite, and acidified montmorillonite in Example 1, and the obtained nitrogen adsorption-desorption curve is asFigure 1 As shown, Bentonite represents bentonite, MMT represents montmorillonite, and A-MMT represents acidified montmorillonite. The following table shows the specific surface area and average pore size of bentonite, montmorillonite and acidified montmorillonite in Example 1.

[0051] Table 1 Specific surface area and average pore size of bentonite, montmorillonite and acidified montmorillonite

[0052]

[0053] According to the IUPAC classification standards, Figure 1 All samples showed type IV adsorption isotherms and H3 type hysteresis loops. As can be seen from the table, the amount of nitrogen adsorbed by bentonite is very small, indicating that it is almost a non-porous material and contains more impurities. After purification, the nitrogen adsorption of the obtained montmorillonite doubled, indicating that the montmorillonite was successfully purified and the obtained montmorillonite had a certain pore volume. Compared with montmorillonite, the N2 adsorption of the acidified montmorillonite in the low pressure area (p / p0<0.1) increased, indicating that montmorillonite will produce some micropores after acid activation. While the specific surface area increases, the H+ hydrolyzed during the acidification process can replace the metal cations between the montmorillonite layers, thereby weakening the interaction between the solid layers. The permanent negative charge of the acidified montmorillonite increases, which is more conducive to cation exchange, so the adsorption capacity of pesticides is improved.

[0054] 2. Test the sustained release performance of the pH-responsive nanocellulose crystal-based hydrogel balls obtained in Example 1-3. Under the experimental conditions of step (4) of Example 1-3, take out the supernatant after 2mL of the assembled powder in Example 1-3 is dispersed in the pesticide solution to measure the absorbance value, calculate the concentration of fipronil in the solution according to the standard curve equation, and then obtain the amount of fipronil encapsulated and loaded. The encapsulation rate formula is calculated as follows: Encapsulation rate (%) = effective mass of fipronil / total mass of fipronil input × 100%. The load rate formula is calculated as follows: Load rate (%) = effective mass of fipronil / total mass of hydrogel balls after drying × 100%. Use phosphate buffer to simulate soil environments with different pH values, accurately weigh 0.2g of hydrogel balls in Example 1-3 and add them to 30mL of buffer, draw a sustained release curve according to the change of pesticide concentration in the solution over time, and record the highest release rate of pesticide after 120h.

[0055] Table 2 Encapsulation efficiency, loading rate and maximum release rate of the hydrogel ball for fipronil after 120 hours

[0056]

[0057] As can be seen from Table 2, the pH-responsive nanocrystalline cellulose-based hydrogel spheres of the present invention have a high encapsulation rate and loading rate for fipronil in organic solvents. The encapsulation rate is above 64.1 wt%, the loading rate is above 67.3 wt%, and in soil environments with different pH values, the maximum pesticide release rate after 120 h is above 59.7%.

[0058] Figure 2 Figure 4 is the ultraviolet spectrum of the pesticide in the pH-responsive nanocrystalline cellulose-based hydrogel spheres in Example 1 over time. An ultraviolet-visible spectrophotometer was used to evaluate the stability of the encapsulated fipronil during the sustained release process. As Figure 2 shown, the absorbance peak of fipronil did not change significantly, indicating that fipronil is stable in phosphate buffer, similar to pure fipronil.

[0059] Figure 3 Figure 5 is the release rate curve of the pH-responsive nanocrystalline cellulose-based hydrogel spheres in Example 1 under different pH conditions within 120 h. As Figure 3 can be seen, the release rate of the pesticide in the hydrogel spheres increases with the increase of pH, indicating that the hydrogel spheres of the present invention can achieve the purpose of adjusting the pesticide release rate by adjusting the pH.

Claims

1. A preparation method of a pH-responsive pesticide slow-release hydrogel ball, characterized in that, It includes the following steps: (1) Preparation of polyethylenimine-modified nanocrystalline cellulose: Take an aqueous solution of polyethylenimine and add it to a suspension of carboxylated nanocrystalline cellulose. Continuously stir, adjust the pH value of the mixed solution to 1-3 with concentrated hydrochloric acid, continue stirring, centrifuge, wash the obtained precipitate, and freeze-dry to obtain polyethylenimine-modified nanocrystalline cellulose powder; the mass fraction of the aqueous solution of polyethylenimine is 1-5 wt%, and the mass fraction of the suspension of carboxylated nanocrystalline cellulose is 1-5 wt%; (2) Preparation and pretreatment of montmorillonite: Add a dispersant to the bentonite slurry, stir, let it stand for sedimentation, centrifuge, dry, grind, and sieve the obtained supernatant. Disperse the obtained montmorillonite in an HCl solution, stir, and after washing, filtering, drying, and grinding, obtain pretreated montmorillonite powder; the dispersant is any one or a combination of two or more of sodium hexametaphosphate, sodium pyrophosphate, and sodium silicate; (3) Preparation of the assembly: Disperse the pretreated montmorillonite powder and the polyethylenimine-modified nanocrystalline cellulose powder in water respectively to obtain a pretreated montmorillonite suspension and a polyethylenimine-modified nanocrystalline cellulose suspension; dropwise add the obtained pretreated montmorillonite suspension to the obtained polyethylenimine-modified nanocrystalline cellulose suspension, continuously stir to obtain an assembly suspension, and after freeze-drying, obtain assembly powder; the mass fraction of the pretreated montmorillonite suspension is 0.2-0.5 wt%, and the mass fraction of the polyethylenimine-modified nanocrystalline cellulose suspension is 0.8-1 wt%; the mass ratio of the pretreated montmorillonite and polyethylenimine-modified nanocrystalline cellulose contained in the assembly powder is 1:1-5; (4) Preparation of pH-responsive pesticide slow-release hydrogel beads: Disperse the assembly powder in a pesticide solution, after shaking, centrifuging, washing, and drying, disperse the obtained pesticide-loaded assembly powder in water, add sodium alginate, and dropwise add it to a CaCl2 solution under stirring conditions. After standing, washing, and vacuum drying, obtain pH-responsive pesticide slow-release hydrogel beads; the mass-to-volume ratio of the assembly powder to the pesticide solution is 1 g: 200-250 mL; the mass ratio of the pesticide-loaded assembly powder to sodium alginate is 1:0.5-1.

2. The preparation method of the pH-responsive pesticide slow-release hydrogel ball according to claim 1, wherein In step (1), the diameter of the carboxylated nanocrystalline cellulose is 4-10 nm, the length is 100-500 nm, and the surface carboxyl content is 1.8-2 mmol / g.

3. A pH-responsive pesticide slow-release hydrogel bead prepared by the method for preparing a pH-responsive pesticide slow-release hydrogel bead according to claim 1 or 2.

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