An amphiphilic xylan polymer, its preparation and its application in pesticide formulations

Abstract

The present invention discloses an amphiphilic xylan polymer, its preparation method and its application in pesticide formulations. The preparation method of the amphiphilic xylan polymer comprises the following steps: dissolving xylan and lauric acid in dimethyl sulfoxide, then adding a coupling agent N,N'-dicyclohexylcarbodiimide and a catalyst 4-dimethylaminopyridine, reacting under a protective gas atmosphere, then centrifuging to remove the reaction by-product N-N'-dicyclohexylurea, washing with absolute ethanol, and then extracting and purifying with a mixed solution of acetone and isopropanol, and drying under vacuum to obtain a xylan grafted lauric acid polymer, that is, the amphiphilic xylan polymer. The amphiphilic xylan polymer prepared by the present invention can improve the storage stability and wettability when used as a pesticide carrier for preparing abamectin aqueous emulsion, providing an effective way for the development of green pesticide formulations.

Description

Technical Field

[0001] The present invention relates to the field of pesticide formulations, and particularly to an amphiphilic xylan polymer, its preparation, and its application in pesticide formulations. Background Art

[0002] Pesticides are the most effective means for controlling pests and diseases. However, for a long time, due to limitations in pesticide formulations, environmental conditions, application methods, and other application conditions, the effective utilization rate of pesticides is low, resulting in excessive use of pesticides, and thus problems such as excessive pesticide residues and environmental pollution. In recent years, the use of nanomaterials and advanced process technologies to prepare efficient and safe green pesticide formulations can improve the dispersibility and stability of pesticides, while promoting the adhesion and deposition of pesticides on target crops, reducing the dosage and residual pollution of pesticides, and thus achieving the reduction of pesticide application and the increase of efficiency. Abamectin is a new type of biological pesticide with broad-spectrum insecticidal, acaricidal, and nematicidal activities. However, abamectin has poor photostability and solubility, is easily decomposed under ultraviolet light irradiation, and leads to an increase in the actual dosage during the application process, thus causing harm to plants and the environment. Using nanomicelles as carriers for abamectin can improve the solubility and stability of abamectin.

[0003] Nanomicelles with a core-shell structure formed by self-assembly of amphiphilic block polymers are a new type of nanomaterial with excellent physical and chemical properties such as quantum effects, small size effects, and surface interface effects. When used to load poorly soluble pesticide molecules, they can improve the stability and dispersibility of poorly soluble pesticides. This is because the hydrophobic region in the micelle core can load hydrophobic pesticide molecules, increasing their solubility and stability, while the hydrophilic outer shell of the micelle separates the encapsulated molecules inside from the external environment, preventing the interaction of the encapsulated molecules and the influence of the external environment, thereby improving the stability of pesticide molecules.

[0004] Xylan is the most abundant natural polymer in nature after cellulose, and has the advantages of wide sources, low cost, good biodegradability and biocompatibility. Moreover, the degradation products will not cause secondary pollution to the environment, and it is an ideal green pesticide carrier. However, commercially available xylan usually shows different water solubilities due to different extraction sources and methods, and cannot well embed drugs or form complexes with them. Currently, the methods for modifying xylan mainly focus on grafting active groups onto xylan (such as Chinese Patent Application CN108079001A), or preparing hydrogels (such as Chinese Patent Application CN111961230A) to achieve the delivery of drugs or biological macromolecules, or enhancing the medicinal activity of xylan itself after modification (such as Chinese Patent Applications CN110698594A, CN111961144A).

[0005] Amphiphilic compounds are composed of a hydrophilic end and a hydrophobic end. They can self-assemble into micelles in water. The cavity of the hydrophobic end can interact with various hydrophobic drugs and stabilize them in an aqueous solution, while the hydrophilic end can protect the drugs from the external environment. There has been no report on the modification of xylan to synthesize amphiphilic compounds and their application in pesticides. Therefore, it is urgently necessary to develop a xylan carrier that has an easily accessible lipophilic end, a simple preparation process, a low preparation cost, and can be applied to pesticides. Summary of the Invention

[0006] The first object of the present invention is to overcome the disadvantages and deficiencies of the prior art and provide a preparation method of an amphiphilic xylan polymer.

[0007] The second object of the present invention is to provide the amphiphilic xylan polymer prepared by the above method.

[0008] The third object of the present invention is to provide the application of the amphiphilic xylan polymer in the preparation of pesticide carriers or pesticide formulations.

[0009] The fourth object of the present invention is to provide a 4.4% abamectin aqueous emulsion.

[0010] The fifth object of the present invention is to provide a preparation method of the 4.4% abamectin aqueous emulsion.

[0011] The sixth object of the present invention is to provide the application of the 4.4% abamectin aqueous emulsion in pest control.

[0012] The objects of the present invention are achieved by the following technical solutions:

[0013] A preparation method of an amphiphilic xylan polymer, comprising the following steps:

[0014] Dissolve xylan and lauric acid in dimethyl sulfoxide (DMSO), then add a coupling agent N,N'-dicyclohexylcarbodiimide (DCC) and a catalyst 4-dimethylaminopyridine (DMPA), react under a protective gas atmosphere, then centrifuge to remove the reaction by-product N-N'-dicyclohexylurea, wash with absolute ethanol, and then extract and purify with a mixed solution of acetone and isopropanol, and obtain a xylan grafted lauric acid polymer, that is, the amphiphilic xylan polymer after vacuum drying.

[0015] The mass ratio of the xylan to the lauric acid is 1-2:2; preferably 1-1.5:2; more preferably 1.32:2.

[0016] The mass ratio of the coupling agent N,N'-dicyclohexylcarbodiimide (DCC) to the catalyst 4-dimethylaminopyridine (DMPA) is 6-7:1; preferably 6-6.5:1; more preferably 6.24:1.

[0017] The mass ratio of the total mass of the coupling agent and the catalyst to the mass of xylan is 1:1.5 - 2; preferably 1:1.81.

[0018] The dosage of the dimethyl sulfoxide is calculated as 35 - 40 mL of dimethyl sulfoxide per gram of xylan.

[0019] The protective gas is nitrogen.

[0020] The reaction time is 60 - 120 minutes.

[0021] The volume ratio of acetone to isopropanol in the acetone and isopropanol mixed solution is preferably 1:1.

[0022] An amphiphilic xylan polymer is prepared by the method described in any one of the above.

[0023] The application of the amphiphilic xylan polymer in the preparation of a pesticide carrier or a pesticide formulation.

[0024] The pesticide is preferably abamectin; preferably the abamectin B1a technical material.

[0025] A 4.4% abamectin aqueous emulsion contains the following components by mass percentage: 4.4% abamectin, 1 - 2% of the above amphiphilic xylan polymer, 24 - 25% cyclohexanone, 3 - 5% emulsifier T - 028, 2 - 6% emulsifier Z - 029, and the balance is water.

[0026] The 4.4% abamectin aqueous emulsion preferably contains the following components by mass percentage: 4.4% abamectin, 2% of the above amphiphilic xylan polymer, 25% cyclohexanone, 5% emulsifier T - 028, 6% emulsifier Z - 029, and the balance is water.

[0027] The water is preferably deionized water.

[0028] The preparation method of the 4.4% abamectin aqueous emulsion includes the following steps:

[0029] (1) Dissolve abamectin in cyclohexanone, add emulsifier T - 028, and stir evenly to obtain the oil phase;

[0030] (2) Add the above amphiphilic xylan polymer (X - LA) to water and dissolve it with ultrasonic assistance to obtain the X - LA solution;

[0031] (3) Add the X - LA solution to the oil phase, keep it at a constant temperature of 50 °C and shake it evenly, then add emulsifier Z - 029, add water to make up to 100% under stirring conditions, and continue to shake it evenly at a constant temperature of 50 °C to obtain the 4.4% abamectin aqueous emulsion.

[0032] The concentration of the X-LA solution described in step (3) is preferably 72 mg / mL.

[0033] The time of constant temperature shaking and mixing in step (3) is all more than 30 min.

[0034] Application of the described 4.4% abamectin aqueous emulsion in controlling pests.

[0035] The described pests include at least one of mites, nematodes, Spodoptera litura, Plutella xylostella, and Pomacea canaliculata, etc.

[0036] The present invention has the following advantages and effects compared with the prior art:

[0037] The present invention first uses lauric acid to carry out amphiphilic graft modification on xylan to prepare xylan grafted lauric acid polymer (X-LA), and then uses it as a pesticide carrier to prepare 4.4% abamectin aqueous emulsion. This aqueous emulsion has good storage stability (low temperature stability and thermal storage stability) and wetting performance, providing an effective way for the development of green pesticide formulations of amphiphilic xylan polymers. Description of the Drawings

[0038] Figure 1 It is a synthesis process diagram of the xylan grafted lauric acid polymer of the present invention.

[0039] Figure 2 It is an FTIR spectrum of the polysaccharide and xylan grafted lauric acid polymer of the present invention.

[0040] Figure 3 It is of the xylan and xylan grafted lauric acid polymer of the present invention 1 1H-NMR spectrum.

[0041] Figure 4 It is a transmission electron micrograph of xylan grafted lauric acid polymer (X-LA), 4.4% abamectin aqueous emulsion, and commercial aqueous emulsion; among them, A is X-LA; B is 4.4% abamectin aqueous emulsion; C is commercial aqueous emulsion.

[0042] Figure 5 It is a particle size change diagram of 4.4% abamectin aqueous emulsion and commercial aqueous emulsion under different storage conditions.

[0043] Figure 6 It is a particle size distribution diagram of 4.4% abamectin aqueous emulsion and commercial aqueous emulsion under different storage conditions; among them, A is 4.4% abamectin aqueous emulsion; B is commercial aqueous emulsion.

[0044] Figure 7 It is a surface tension change diagram of 4.4% abamectin aqueous emulsion and commercial aqueous emulsion under different storage conditions.

[0045] Figure 8 It is a statistical chart of the liquid retention rate of 4.4% abamectin aqueous emulsion and commercial aqueous emulsion on cabbage leaves. Detailed implementation mode

[0046] The present invention will be further described in detail below in conjunction with embodiments, but the implementation mode of the present invention is not limited thereto. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field. The test methods without specific experimental conditions in the following embodiments are usually carried out according to conventional experimental conditions or according to the experimental conditions recommended by the manufacturer. Unless otherwise specified, the reagents and raw materials used in the present invention can be obtained through commercial channels.

[0047] Example 1

[0048] 1. Materials and methods

[0049] 1.1 Materials and instruments

[0050] 1.1.1 Test materials

[0051] Abamectin B1a technical (purity 97%, CAS No.: 65195-55-3); xylan (molecular weight (150.13000)n, purity 99%, CAS Registry No.: 9014-63-5); lauric acid (LA), dimethyl sulfoxide (DMSO), N,N'-dicyclohexylcarbodiimide (DCC) and 4-dimethylaminopyridine (DMPA) are all of analytical grade (Aladdin Reagent Co., Ltd.); acetone, isopropanol, cyclohexanone and absolute ethanol are all of analytical grade (Guangzhou Chemical Reagent Factory); emulsifier Z-029, emulsifier T-028 (purchased from Guangzhou Yueyouyan Optoelectronic Materials Co., Ltd.); commercial 4.4% abamectin aqueous emulsion (purchased from Jiangmen Plant Protection Co., Ltd.).

[0052] 1.1.2 Test instruments

[0053] RW20 stirrer (IKA Company, Germany); centrifuge; DZF-6055 vacuum drying oven (Shanghai Yiheng Scientific Instrument Co., Ltd.); TEN-SOR27 Fourier transform infrared spectrometer (Bruker Company, Germany); AVⅢ-400MHz nuclear magnetic resonance spectrometer (Bruker Company, Germany); KQ-600GKDV ultrasonic cleaner (Kunshan Ultrasonic Instrument Co., Ltd.); JET-2100 transmission electron microscope (JEOL Ltd., Japan); Nano-ZS&MPT-2 dynamic light scattering instrument (Malvern Instruments Ltd., UK); ZJ-7000 optical contact angle measuring instrument (Shenzhen Zhijia Instrument Equipment Co., Ltd.); SHZ-B constant temperature water bath oscillator (Jintan City Chengxi Chunlan Instrument Factory).

[0054] 1.2 Test methods

[0055] 1.2.1 Preparation and Characterization of Amphiphilic Xylan Polymer

[0056] The synthesis process of xylan grafted lauric acid polymer is as Figure 1 shown. Xylan grafted lauric acid polymer (X-LA) is an amphiphilic substance obtained by grafting lauric acid molecules onto the xylan backbone through an esterification reaction. The preparation steps are as follows:

[0057] Weigh 6.6 g of xylan and add it to 150 mL of dimethyl sulfoxide to obtain a lauric acid / DMSO solution; weigh 10.016 g of lauric acid and add it to 50 mL of dimethyl sulfoxide to obtain a xylan / DMSO solution; weigh 10.3 g of coupling agent DCC and add it to 50 mL of dimethyl sulfoxide to obtain a DCC / DMSO solution; then add the lauric acid / DMSO solution to the xylan / DMSO solution and stir for 10 min. Slowly add 1.65 g of catalyst DMAP, and then dropwise add the DCC / DMSO solution (in the reaction system, the mass ratio of xylan to lauric acid is about 1.32:2, and the mass ratio of coupling agent DCC to catalyst DMPA is about 6.24:1; the total addition amount of the coupling agent and the catalyst is 1.81 parts (mass ratio) of the coupling agent and the catalyst added per 1 part of xylan). Pass nitrogen for protection and react at room temperature for 60 - 120 minutes. Then remove the reaction by-product N-N'-dicyclohexylurea by centrifugation, wash with absolute ethanol, extract and purify with acetone / isopropanol (v:v = 1:1), and dry in vacuum to obtain the product. The product is characterized by a TENSOR27 Fourier transform infrared spectrometer and an AVⅢ-400MHz nuclear magnetic resonance spectrometer, and the degree of substitution is calculated.

[0058] 1.2.2 Preparation of 4.4% Abamectin Emulsion in Water

[0059] It is prepared by the phase inversion method. Dissolve the abamectin technical in an appropriate amount of cyclohexanone, add a small amount of emulsifier T-028, and stir evenly as the oil phase; add the xylan grafted lauric acid polymer (X-LA) to ultrapure water and dissolve it with ultrasonic assistance to prepare an X-LA solution with a concentration of 72 mg / mL. Take a small amount of the X-LA solution and add it to the oil phase. Keep it at a constant temperature of 50 °C and shake for 30 min. Then add a small amount of emulsifier Z-029, make up deionized water to 100 g, and continuously stir while adding water to complete the phase inversion process. Keep it at a constant temperature of 50 °C and shake for 30 min to obtain a 4.4% (W / V) abamectin emulsion in water. The mass fractions of abamectin, cyclohexanone, X-LA, emulsifier T-028, and emulsifier Z-029 in the emulsion in water are 4.4%, 25%, 2%, 5%, and 6% respectively.

[0060] 1.2.3 Determination of Storage Stability of Avermectin Emulsion in Water

[0061] According to the methods of national standards GB / T 19136-2021 and GB / T 19137-2003, the 4.4% avermectin emulsion in water samples were placed at (54±2)°C for 14 days and at (0±2)°C for 7 days respectively. The thermal storage stability and low-temperature stability of 4.4% avermectin emulsion in water (Avermectin EW) and commercial emulsion in water (Commercial EW) were tested respectively. Standing at room temperature for 14 days was used as a control. According to the method of GB 2763-2021, the change in the content of the active ingredient of avermectin in the emulsion in water was determined, and a commercially available 5% avermectin emulsion in water was used as a control, and the degradation rate of avermectin under various storage conditions was calculated:

[0062]

[0063] 1.3 Characterization of the Properties of Avermectin Emulsion in Water

[0064] 1.3.1 Morphology Observation

[0065] The 4.4% avermectin emulsion in water and the commercial emulsion in water were diluted to a certain concentration (1:500, v / v) respectively. A small amount of the diluted solution was dropped on a 200-mesh copper mesh. After natural air drying for 2 minutes, it was negatively stained with freshly prepared 2% (w / v) phosphotungstic acid for 2 minutes. After drying at room temperature, the morphology was observed through a JET-2100 transmission electron microscope (TEM).

[0066] 1.3.2 Particle Size and Its Distribution

[0067] The 4.4% avermectin emulsion in water and the commercial emulsion in water were diluted 1000 times respectively. A small amount of the diluted solution was filtered through a 0.45 μm filter membrane. The particle size and its distribution of the emulsion were measured respectively by a Nano-ZS&MPT-2 dynamic light scattering instrument at a 90° scattering angle. It was repeated 3 times and the average value was taken.

[0068] 1.3.4 Zeta Potential Determination

[0069] The Zeta potential of 4.4% avermectin emulsion in water and commercial emulsion in water was measured respectively by a Nano-ZS&MPT-2 dynamic light scattering instrument. It was repeated 3 times and the average value was taken.

[0070] 1.3.5 Surface Tension Determination

[0071] After the 4.4% avermectin emulsion in water and the commercial emulsion in water were diluted 1000 times respectively, the surface tension was determined by the sessile drop method through a ZJ-7000 optical contact angle measuring instrument, with ultrapure water as a control. It was repeated 10 times and the average value was taken.

[0072] 1.3.6 Determination of Liquid Retention Rate on Cabbage Leaves

[0073] Measure the liquid retention rate of the medicament on cabbage leaves: Use a hole punch to cut fresh cabbage leaves (cabbage at the six-leaf stage) with a uniform size of 6.6 cm in diameter, soak them in 4.4% abamectin aqueous emulsion (diluted 1:1000 times) and commercial aqueous emulsion (diluted 1:1000 times) for 1 min respectively, lift them vertically, and weigh them when the leaves stop dripping the solution. Use ultrapure water as a control, repeat 3 times, and take the average value.

[0074] The formula for the liquid retention rate is as follows:

[0075] Liquid retention rate = (m1 - m0) / A (1)

[0076] In the formula, m0 and m1 are the weights of the leaves before and after soaking respectively, and A is the leaf surface area.

[0077] 1.4 Determination of Encapsulation Efficiency and Loading Capacity of Abamectin Loaded with X-LA as a Drug Carrier

[0078] The encapsulation efficiency and loading capacity of abamectin capsules (4.4% abamectin aqueous emulsion) using X-LA as a carrier were determined by the method of GB 2763-2021 and calculated according to the following formula:

[0079]

[0080]

[0081] 2. Results and Analysis

[0082] 2.1 Results of Structural Characterization of Amphiphilic Hemicellulose Derivatives

[0083] Figure 2 It is the FTIR spectrum of xylan and xylan grafted lauric acid polymer (X-LA). After grafting lauric acid onto xylan, obvious changes occurred in the FT-IR spectrum. The absorption peaks at 1744 cm -1 and 1256 cm -1 are the characteristic absorption peaks of the ester carbonyl group (C=O) and ether bond (C-O) on the lauric acid side chain respectively, indicating that the lauric acid side chain was successfully grafted onto the main chain of the xylan molecule.

[0084] Figure 3 It is the 11H-NMR spectrum. In the spectrum of xylan, there are extremely weak signal peaks near 1.22 ppm and 0.84 ppm. This is because xylan is a polysaccharide composed of multiple sugar groups, and there are very small amounts of CH2 and CH3 on the branched chains. After grafting lauric acid onto xylan, stronger signal peaks appear at 1.23 ppm and near 0.84 ppm. Among them, 0.84 ppm is the chemical shift of the methyl group (CH3) on the side-chain lauric acid molecule, while the stronger signal peaks at 1.23, 1.49, and 2.26 ppm correspond to the chemical shifts of the methylene group (CH2) on the side-chain lauric acid molecule, indicating that the hydrophobic side chain of lauric acid has been successfully grafted onto the xylan molecular chain.

[0085] According to formula (2), the degree of substitution (DS) of lauric acid in the xylan graft polymer can be calculated as follows:

[0086]

[0087] In the formula, Ia, I H1 , I H4 respectively represent the integral areas of the chemical shifts of the H on the methyl group (CH3) of the hydrophobic side chain and the H1 and H4 on the hemicellulose structural unit. In this study, the degree of substitution of the xylan graft lauric acid polymer is approximately 0.318.

[0088] 2.2 Performance characterization of the emulsion in water

[0089] 2.2.1 Morphology observation

[0090] The transmission electron micrographs of X-LA, 4.4% abamectin emulsion in water, and the commercial emulsion in water are as Figure 4 shown. The amphiphilic xylan polymer (X-LA) self-assembles to form spherical nanostructured micelles with a particle size of less than 100 nm ( Figure 4 A). The particles of the 4.4% abamectin emulsion in water prepared with X-LA maintain the morphological size of the X-LA micelles, and the particle morphology is clearly visible, showing a smooth spherical shape ( Figure 4 B). However, the particles of the commercial emulsion in water are irregular in shape, and the particle distribution is disorderly, with a particle size greater than 100 nm ( Figure 4 C).

[0091] 2.2.2 Results of storage stability

[0092] The performance characterization of the 4.4% abamectin emulsion in water prepared in this invention under different storage conditions is shown in Table 1, the degradation rate of abamectin under different storage conditions is shown in Table 2, the particle size change is as Figure 5 shown, and the particle size distribution is as Figure 6 shown. From Figure 5It can be seen that after cold storage, the indicators of the 4.4% abamectin aqueous emulsion prepared with X-LA are similar to those stored at room temperature. The average particle size after heat storage is only 122.9 nm, the PDI index is about 0.2, and there is only one particle size distribution peak under different storage conditions ( Figure 6 A). The total active ingredient content remains unchanged (Table 1), indicating that the 4.4% abamectin aqueous emulsion prepared with X-LA has good dispersibility, uniform distribution of emulsion particles, and good storage stability, especially heat storage stability. However, obvious chromatography phenomena occur in the commercial aqueous emulsion after cold storage and heat storage. Among them, the average particle size after heat storage increases from 156.2 nm to 588.9 nm ( Figure 5 ), the PDI index is 0.61, and three particle size distribution peaks appear after heat storage ( Figure 6 B). Obvious aggregation of emulsion particles occurs, indicating that the commercial aqueous emulsion has poor storage stability, especially heat storage stability.

[0093] In addition, by comparing the particle sizes of the aqueous emulsion particles in Table 1 and Figure 4 in the water emulsion, it can be found that the particle size of the particles in the TEM image is smaller than the average particle size obtained by dynamic light scattering method, which may be due to the error of the detection method. The dynamic light scattering method detects the hydrodynamic diameter of the solvated micelles, while the TEM image is observed under high vacuum conditions, and the micelles undergo a certain degree of dehydration shrinkage during this process.

[0094] The same conclusion can be obtained by analyzing the surface Zeta potential of the aqueous emulsion (Table 1). Under the same conditions, the Zeta potential value of the 4.4% abamectin aqueous emulsion is higher than that of the commercial aqueous emulsion. The higher surface charge value makes the particles repel each other due to electrostatic interaction and is not easy to aggregate, thus improving the stability of the aqueous emulsion.

[0095] Table 1 Performance characterization of 4.4% abamectin aqueous emulsion under different storage conditions

[0096]

[0097]

[0098] Table 2 Degradation rate of abamectin under different storage conditions

[0099]

[0100] 2.2.3 Wetting performance results

[0101] The wetting performance of the liquid medicine is a key factor affecting the effective utilization rate of pesticides. Good wetting performance can promote the wetting, spreading and deposition of the liquid medicine on the target crops.

[0102] Figure 7The surface tension results of the aqueous emulsion. The surface tension of the 4.4% abamectin aqueous emulsion prepared with X-LA was about 52 mN / m under different storage conditions, which was lower than that of ultrapure water. The surface tension of the commercial aqueous emulsion increased after cold storage and heat storage. Therefore, the 4.4% abamectin aqueous emulsion had a lower surface tension and higher stability under different storage conditions compared with the commercial aqueous emulsion.

[0103] Figure 8 The liquid retention rate of the aqueous emulsion on cabbage leaves. From Figure 8 it can be seen that the liquid retention rate of the 4.4% abamectin aqueous emulsion on cabbage leaves was greater than that of ultrapure water, while that of the commercial aqueous emulsion was less than that of ultrapure water. This was because the 4.4% abamectin aqueous emulsion prepared with X-LA had a lower surface tension ( Figure 7 ), and it was easy to wet and spread on cabbage leaves. In addition, X-LA was an amphiphilic hemicellulose polymer, similar to the hydrophobically modified cellulose polymer, and it was a non-ionic surfactant. Adding a non-ionic surfactant could reduce the interfacial tension of cabbage leaves (superhydrophobic interface), thus inhibiting the splashing of the solution and enabling the pesticide to adhere and deposit on cabbage leaves.

[0104] 2.3 Encapsulation efficiency and drug loading capacity of abamectin loaded with X-LA as a drug carrier

[0105] The encapsulation efficiency and drug loading capacity of abamectin (4.4% abamectin aqueous emulsion) loaded with X-LA as a drug carrier reached 65.72% and 4.40% respectively (Table 3).

[0106] Table 3 Encapsulation efficiency and drug loading capacity of abamectin loaded with X-LA

[0107] Sample Entrapment efficiency / % Drug loading / % X-LA Loaded Avermectin Capsules 65.72 4.40

[0108] As a natural polymer material, xylan has the advantages of wide source, low cost, good biocompatibility and biodegradability. The nano-pesticide preparation with it as a carrier can reduce the dosage of pesticides, realize the target release of pesticide active substances, thus improving the pesticide utilization rate and reducing pesticide residues. Moreover, xylan is biodegradable, and the degradation products do not cause secondary pollution and are environmentally friendly.

[0109] The nano-micelles with a "core-shell" structure formed by the self-assembly of amphiphilic block polymers are excellent carriers for poorly soluble pesticides. Their small size and large specific surface area can improve the dispersibility and stability of poorly soluble pesticide molecules. In addition, some amphiphilic natural polymer polymers can be used as non-ionic surfactants. After adding them to pesticides, they can inhibit the splashing of the liquid medicine on the cabbage (superhydrophobic interface) leaf surface, increase the adhesion and deposition of pesticides on the target crops, improve the wetting performance of pesticides, and thus improve the pesticide utilization rate.

[0110] In the present invention, xylan was hydrophobically grafted and modified with lauric acid to prepare an amphiphilic xylan polymer (X-LA), which was used in the development of 4.4% abamectin aqueous emulsion. By characterizing the particle size, Zeta potential, surface tension of 4.4% abamectin aqueous emulsion under different storage conditions and the liquid retention rate on cabbage leaves, it was proved that the 4.4% abamectin aqueous emulsion prepared with X-LA had good storage stability (thermal storage stability and low temperature stability) and wetting properties. The above results can provide a reference for the preparation of aqueous emulsions with good storage stability and wettability.

[0111] Nanomicelles are ordered aggregates with a "core-shell" structure formed by the self-assembly of amphiphilic block polymers, and their hydrophobic core can load poorly soluble pesticides.

[0112] Developing new nano-pesticide formulations using nanomaterials and preparation technologies can effectively improve the utilization rate of pesticides, reduce pesticide residues and environmental pollution. This is because the small size and large specific surface area of nanoparticles can improve the dispersibility, wettability and stability of poorly soluble pesticides, and increase the adhesion and deposition of pesticides on the target surface.

[0113] In the present invention, compared with commercial aqueous emulsions, the 4.4% abamectin nanomicelle aqueous emulsion prepared with hemicellulose-lauric acid polymer had good storage stability, especially thermal storage stability. Under different storage conditions, there was only one particle size distribution peak, and the total content of active ingredients remained unchanged. The average particle sizes of the nanomicelle aqueous emulsion after storage at normal temperature and cold storage were 225.5 nm and 229.8 nm respectively, while the average particle size after thermal storage was only 122.9 nm, and the surface Zeta potential was -7.677 mV. This is because the encapsulation of abamectin by micelles increased the stability of abamectin in water. Secondly, the unique small size and large specific surface area effects of nanomicelles made the smaller particles have better dispersibility and stability in water, and the negative charges carried on the particle surface also promoted their stability.

[0114] Compared with commercial aqueous emulsions, the 4.4% abamectin nanomicelle aqueous emulsion prepared had good wetting properties. The surface tension under different storage conditions remained at about 52 mN / m, showing good hydrophilic properties and stability. In addition, the liquid retention rate of the nanomicelle aqueous emulsion on cabbage leaves was higher than that of water and the control group. This is because the amphiphilic polymer itself has a surface active effect and can inhibit the splashing of the micelle solution on the cabbage leaves (superhydrophobic interface), so that the pesticide liquid adheres and deposits on the cabbage leaves.

[0115] Therefore, the nanomicelles formed by the self-assembly of amphiphilic hemicellulose polymers can be used as excellent carriers for abamectin, and their application in abamectin nano-formulations can improve the application effect. It is expected that such formulations will play an important role in the prevention and control of pests and diseases such as Spodoptera litura and Plutella xylostella.

[0116] The above embodiments are preferred embodiments of the present invention. However, the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A 4.4% abamectin aqueous emulsion, characterized in that, It is composed of the following components by mass percentage: 4.4% abamectin, 1-2% amphiphilic xylan polymer, 24-25% cyclohexanone, 3-5% emulsifier T-028, 2-6% emulsifier Z-029, and the balance is water; The amphiphilic xylan polymer is prepared by the following method: Dissolve xylan and lauric acid in dimethyl sulfoxide, then add coupling agent N,N'-dicyclohexylcarbodiimide and catalyst 4-dimethylaminopyridine, react under a protective gas atmosphere, then centrifuge to remove the reaction by-product N-N'-dicyclohexylurea, wash with absolute ethanol, and then extract and purify with a mixed solution of acetone and isopropanol, and obtain xylan grafted lauric acid polymer, that is, the amphiphilic xylan polymer after vacuum drying; The mass ratio of the xylan to the lauric acid is 1-2:

2.

2. The 4.4% abamectin aqueous emulsion according to claim 1, characterized in that: The mass ratio of the coupling agent N,N'-dicyclohexylcarbodiimide to the catalyst 4-dimethylaminopyridine is 6-7:1; The total mass ratio of the coupling agent and the catalyst to the mass of xylan is 1:1.5-2.

3. The 4.4% abamectin aqueous emulsion according to claim 1, characterized in that: The reaction time is 60-120 minutes; The volume ratio of acetone to isopropanol in the mixed solution of acetone and isopropanol is 1:

1.

4. The 4.4% abamectin aqueous emulsion according to claim 1, characterized in that, It is composed of the following components by mass percentage: 4.4% abamectin, 2% amphiphilic xylan polymer, 25% cyclohexanone, 5% emulsifier T-028, 6% emulsifier Z-029, and the balance is water.

5. A method for preparing the 4.4% abamectin aqueous emulsion according to any one of claims 1 to 4, characterized in that, It includes the following steps: (1) Dissolve abamectin in cyclohexanone, add emulsifier T-028, and stir evenly to obtain an oil phase; (2) Add the amphiphilic xylan polymer to water and dissolve it with ultrasonic assistance to obtain an X-LA solution; (3) Add the X-LA solution to the oil phase, keep it at a constant temperature of 50 °C and shake it evenly, then add emulsifier Z-029, add water to make up to 100% under stirring conditions, and continue to keep it at a constant temperature of 50 °C and shake it evenly to obtain 4.4% abamectin aqueous emulsion.

6. The application of the 4.4% abamectin aqueous emulsion according to any one of claims 1 to 4 in controlling pests.

7. The application according to claim 6, characterized in that: The pests are at least one of mites, nematodes, Spodoptera litura, Plutella xylostella, and Pomacea canaliculata.

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