Environment-friendly nanocapsule loaded with low-melting-point medicine and preparation method of environment-friendly nanocapsule

Abstract

The invention provides an environment-friendly nanocapsule loaded with a low-melting-point medicine and a preparation method of the environment-friendly nanocapsule. According to the method, a biodegradable material is used as a capsule wall, a one-step preparation process is adopted, and the nanocapsule with good drug loading performance is successfully prepared through electrostatic self-assembly of didecyl dimethyl ammonium chloride and sodium lignin sulfonate according to a micro-capsule coating stability maintaining strategy. The obtained nanocapsule is stable in structure, can effectively load low-melting-point drugs, remarkably delays the release rate of the drugs, and meanwhile avoids thermal degradation and activity loss of the drugs in the preparation process.

Description

Technical Field

[0001] The invention belongs to the technical field of pesticide preparations, and particularly relates to an environmentally friendly nanocapsule loaded with a low-melting-point drug and a preparation method thereof. Background Art

[0002] In the field of agricultural pest control, low-melting-point pesticides have become an important means of control due to their unique chemical activity and low preparation cost. However, the low melting point characteristics of this type of pesticide also bring a series of severe challenges. Under normal temperature conditions, low-melting-point pesticides are extremely easy to volatilize and decompose. During storage and transportation, slight fluctuations in temperature may cause changes in their morphology, such as melting and agglomeration, which seriously affect the stability and effectiveness of pesticides. In the pesticide application process, low-melting-point pesticides are susceptible to the combined influence of environmental factors such as light, humidity, and temperature, resulting in significant attenuation of drug efficacy. In order to maintain the control effect, the amount of pesticides used has to be increased, which undoubtedly increases the cost of agricultural production. At the same time, the amount of pesticide residues in the environment increases, posing a potential threat to non-target organisms and the entire ecological environment. Traditional pesticide formulations, such as suspension concentrates and emulsifiable concentrates, are difficult to meet the complex application requirements of low-melting-point pesticides in terms of stability, targeting, and environmental friendliness. Therefore, the development of new delivery systems to break through the bottleneck of existing technologies has become a key issue that the industry needs to solve urgently.

[0003] As an advanced drug encapsulation technology, microcapsule technology uses polymer materials to encapsulate active components such as solids, liquids or gases through chemical or physical methods to form tiny particles, namely microcapsules. This technology provides a new idea for solving the application problems of low-melting-point pesticides. Microcapsules can effectively isolate pesticides from the external environment, and realize the functions of targeted drug delivery, anti-photodecomposition and controlled release. When microcapsules are prepared to the nanometer level, their small particle size, large specific surface area and high surface energy can be fully utilized, which significantly improves the solubility, stability and bioavailability of pesticides. Wrapping low-melting-point pesticides in nanocapsules can form a solid protective barrier, greatly reducing the direct contact between pesticides and the external environment, thereby effectively reducing the volatilization and decomposition rate of pesticides and extending the effective period of pesticides. At the same time, nanocapsules can achieve sustained release and targeted delivery of pesticides, increase the enrichment of pesticides in target sites, and reduce the residue and pollution of pesticides in non-target areas, which is highly consistent with the development needs of modern agriculture for green, environmentally friendly and efficient pesticide formulations.

[0004] However, the existing methods for preparing nanocapsules still have many limitations. Traditional methods for preparing nanocapsules, such as the emulsion-solvent evaporation method and the interfacial polymerization method, usually require the use of a large amount of organic solvents and chemical reagents, which not only increases the preparation cost but also may cause environmental pollution. In relatively mature microencapsulation process schemes at home and abroad, interfacial polymerization mainly uses polyurethane or polyurea as the synthetic wall material, but the wall material metabolizes slowly in the environment and is prone to accumulation after long-term use; in-situ polymerization mainly uses urea-formaldehyde resin and melamine resin, etc., and there is a potential risk to the environment due to the presence of formaldehyde in them.

[0005] In recent years, the use of biodegradable polymer natural polymers, such as alginate, gelatin, and modified cellulose and chitosan, etc. as wall materials has gradually become a research hotspot in microencapsulation. However, limited by factors such as process and cost, the large-scale application of the above methods in the pesticide industry still faces huge challenges.

[0006] In summary, developing an environmentally friendly method for preparing nanocapsules suitable for low-melting-point pesticides has important practical significance and broad application prospects for promoting the innovation and development of pesticide formulation technology, improving the utilization efficiency and control effect of pesticides, and protecting the agricultural ecological environment and the quality and safety of agricultural products. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides an environmentally friendly nanocapsule loaded with low-melting-point drugs and a preparation method thereof.

[0008] The present invention is realized through the following technical solutions: A preparation method of an environmentally friendly nanocapsule loaded with low-melting-point drugs includes the following steps: Weigh the drug, add solvent oil, heat and melt it, add the wall material didecyldimethylammonium chloride to form an oil phase; Weigh the emulsifier and dispersant, add the remaining deionized water, heat and stir until fully and evenly dissolved to form an aqueous phase; Add the prepared oil phase to the aqueous phase, homogenize at high speed, heat the well-mixed emulsion in a water bath, adjust the stirring rate to 300 r / min, and keep it warm for 2 hours to solidify the wall material into capsules.

[0009] Further, the drug is a low-melting-point drug, which is one of fungicides, insecticides, and herbicides.

[0010] Further, the temperature for heating and melting the solvent oil is 40 - 70 °C.

[0011] Further, the ratio of the technical drug to the solvent is 1:1 - 1.5.

[0012] Further, the addition amount of didecyldimethylammonium chloride (DDAC) is 2.4% - 4% of the total mass.

[0013] Furthermore, the emulsifier is selected as 1600s6, and the addition amount is 1%-4% of the total mass.

[0014] Furthermore, the dispersant is selected as sodium lignosulfonate, and the addition amount is 6%-10% of the total mass.

[0015] Furthermore, the temperature difference between the aqueous phase and the oil phase is maintained at 10°C.

[0016] Furthermore, the shear rate is 5000 - 12000 r / min, and the shear time is 3 - 5 min.

[0017] Furthermore, the water bath temperature is maintained at 40 - 60°C.

[0018] The present invention also provides an environmentally friendly nanocapsule loaded with low-melting-point drugs prepared by the above preparation method, and the drug loading amount of the nanocapsule is 1%-30%.

[0019] Compared with the prior art, the present invention has the following technical effects: The present invention uses the capsule shell structure formed by electrostatic self-assembly of DDAC and SL to provide an innovative strategy for controlling Bipolaris maydis. This technology combines the strong bactericidal performance of DDAC with the controlled release and protection functions of the capsule shell, and has the advantages of improving the control effect, reducing environmental pollution, delaying drug resistance, improving thermal stability, resisting rain erosion, and photolysis resistance. Description of the Drawings

[0020] Figure 1 Optical microscope images of the preparations obtained in Examples 1, 17, and 18; Figure 2 Scanning electron microscope images of the preparations obtained in Examples 1, 17, and 18; Figure 3 Nanoparticle size images of the preparations obtained in Examples 1, 17, and 18; Figure 4 Results of encapsulation efficiency determination of the preparations obtained in Examples 1, 17, and 18; Figure 5 Results of cumulative release rate determination of the preparations obtained in Examples 1, 17, and 18 and Comparative Examples 13 - 15; Figure 6 Results of pesticide residue rate determination after photolysis of the preparations obtained in Examples 1, 17, and 18 and Comparative Examples 13 - 15; Figure 7 Pesticide residue rate determination after rain erosion of the preparations obtained in Examples 1, 17, and 18 and Comparative Examples 13 - 15; Figure 8 Results of thermal stability determination of the preparations obtained in Examples 1, 17, and 18 and Comparative Examples 19 - 21. Detailed implementation manners

[0021] The present invention will be described below through specific embodiments to make the technical solutions of the present invention easier to understand and master, but the present invention is not limited thereto. The experimental methods described in the following embodiments are all conventional methods unless otherwise specified; the reagents and materials are all commercially available unless otherwise specified.

[0022] In the following embodiments, the raw material sources are as follows: Table 1. Material sources Example 1 Preparation of 10% pyraclostrobin·flusilazole nanocapsules: (1) Accurately weigh 7.7 g of pyraclostrobin technical and 2.63 g of flusilazole, heat them with 10 g of solvent oil until melted at a melting temperature of 65°C, and add 2.4 g of wall material didodecyldimethylammonium chloride (DDAC) to form an oil phase.

[0023] (2) Accurately weigh 4 g of emulsifier 1600s6 and 6 g of dispersant sodium lignosulfonate, add the remaining deionized water (the total mass is made up to 100 g), and dissolve and mix them fully and evenly at 50°C and 300 rpm to form an aqueous phase.

[0024] (3) Start high-speed homogenization (shearing rate 12000 rpm, 5 min), add the prepared oil phase to the aqueous phase, put the homogenized emulsion into a water bath at 50°C, adjust the stirring rate to 300 rpm, and keep it warm for 2 hours to solidify the wall material into capsules.

[0025] Example 2 The difference between Example 2 and Example 1 is that the melting temperature is 55°C, and the other conditions are exactly the same.

[0026] Example 3 The difference between Example 3 and Example 1 is that the melting temperature is 40°C, and the other conditions are exactly the same.

[0027] Example 4 The difference between Example 4 and Example 1 is that the melting temperature is 70°C, and the other conditions are exactly the same.

[0028] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the melting temperature is 80°C, and the other conditions are exactly the same.

[0029] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the melting temperature is 30°C, and the other conditions are exactly the same.

[0030] Table 2. Influence of Melting Temperature on the Preparation in Examples 1-4 and Comparative Examples 1-2 In Examples 1-4 and Comparative Examples 1-2, the influence of melting temperature was investigated. The results are shown in Table 2. When the temperature was too low, the technical material was not completely dissolved, the oil phase was uneven, solid particles remained, and subsequent emulsification was difficult. When the melting temperature was too high, the wall material decomposed (DDAC might degrade), affecting the chemical stability of the nanocapsules.

[0031] Example 5 The difference between Example 5 and Example 1 is that the addition amount of solvent oil is 15% of the total mass. At this time, the mass ratio of technical material to solvent oil is 2:3, and the other conditions are exactly the same.

[0032] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the addition amount of solvent oil is 20% of the total mass. At this time, the mass ratio of technical material to solvent oil is 1:2, and the other conditions are exactly the same.

[0033] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that the addition amount of solvent oil is 5% of the total mass. At this time, the mass ratio of technical material to solvent oil is 2:1, and the other conditions are exactly the same.

[0034] Table 3. Influence of the Ratio of Technical Material to Solvent on the Preparation in Example 1, 5 and Comparative Examples 3-4 In Example 1, 5 and Comparative Examples 3-4, the influence of solvent oil was investigated. The results are shown in Table 3. As the oil phase carrier, it dissolves the technical materials of pyraclostrobin and flusilazole. When the ratio of technical material to solvent is too low, insufficient dissolution leads to crystallization during cold storage and the preparation fails. When the ratio of technical material to solvent is too high, although the process is not affected, the problems of cost and environmental protection are prominent. Therefore, the ratio of technical material to solvent is limited to 1:1 - 2:3.

[0035] Example 6 The difference between Example 6 and Example 1 is that the addition amount of didodecyldimethylammonium chloride is 3.2% of the total mass, and the other conditions are exactly the same.

[0036] Example 7 The difference between Example 7 and Example 1 is that the addition amount of didodecyldimethylammonium chloride is 4% of the total mass, and the other conditions are exactly the same.

[0037] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that the addition amount of didodecyldimethylammonium chloride is 1.2% of the total mass, and the other conditions are exactly the same.

[0038] Comparative Example 6 The difference between Comparative Example 6 and Example 1 lies in that the addition amount of didecyldimethylammonium chloride is 4.5% of the total mass, and the other conditions are exactly the same.

[0039] Table 4. Effects of the addition amounts of DDAC in Example 1, 6, 7 and Comparative Examples 5 - 6 on the preparation Examples 1, 6, 7 and Comparative Examples 5, 6 were used to explore the effects of didecyldimethylammonium chloride (DDAC). The results are shown in Table 4. As the core material of the capsule wall, the addition amount of DDAC needs to be strictly controlled within 2.4 - 4%. When it is lower than 2.4%, insufficient interfacial coverage leads to capsule wall defects and the preparation fails; when it is higher than 4%, bundle competition and charge neutralization cause aggregation, destroying the nano - capsule structure.

[0040] Example 8 The difference between Example 8 and Example 1 lies in that the addition amount of 1600S6 is 1% of the total mass, and the other conditions are exactly the same.

[0041] Example 9 The difference between Example 9 and Example 1 lies in that the addition amount of 1600S6 is 3% of the total mass, and the other conditions are exactly the same.

[0042] Comparative Example 7 The difference between Comparative Example 7 and Example 1 lies in that the addition amount of 1600S6 is 0.5% of the total mass, and the other conditions are exactly the same.

[0043] Comparative Example 8 The difference between Comparative Example 8 and Example 1 lies in that the addition amount of 1600S6 is 5% of the total mass, and the other conditions are exactly the same.

[0044] Table 5. Effects of the addition amounts of 1600s6 in Example 1, 8, 9 and Comparative Examples 7 - 8 on the preparation Examples 1, 9, 8 and Comparative Examples 7 - 8 were used to explore the effects of 1600S6. As an emulsifier, when the addition amount is lower than 1%, insufficient interfacial coverage leads to droplet coalescence and the stability of the preparation becomes poor; when the addition amount is higher than 4%, micelle competition causes interfacial instability and slight aggregation affects the product quality. Therefore, the limited range is 1% - 4%.

[0045] Example 10 The difference between Example 10 and Example 1 lies in that the addition amount of sodium lignosulfonate is 8% of the total mass, and the other conditions are exactly the same.

[0046] Example 11 The difference between Example 11 and Example 1 lies in that the addition amount of sodium lignosulfonate is 10%, and the other conditions are exactly the same.

[0047] Comparative Example 9 The difference between Comparative Example 9 and Example 1 lies in that the addition amount of sodium lignosulfonate is 5%, and the remaining conditions are exactly the same.

[0048] Comparative Example 10 The difference between Comparative Example 10 and Example 1 lies in that the addition amount of sodium lignosulfonate is 12.5%, and the remaining conditions are exactly the same.

[0049] Table 6. Influence of the addition amount of sodium lignosulfonate on the preparation in Example 1, 10, 11 and Comparative Examples 9 - 10 Example 1, 10, 11 and Comparative Examples 9 - 10 were used to explore the influence of sodium lignosulfonate (SL). The influence results are shown in Table 6. As an anionic surfactant, sodium lignosulfonate (SL) prevents droplet aggregation through electrostatic repulsion (negative charge) and maintains the stability of the emulsion. It crosslinks with the cationic wall material (DDAC) through electrostatic interaction, promotes the solidification of the capsule wall and enhances the mechanical strength. As a key dispersing - crosslinking agent, the addition amount of sodium lignosulfonate (SL) needs to be controlled at 6 - 10%: when the addition amount is less than 6%, the molar ratio of SL to the cationic wall material (DDAC) is unbalanced, resulting in incomplete crosslinking reaction, insufficient solidification of the capsule wall, decreased mechanical strength, and some droplets not forming a complete capsule wall. When the addition amount is excessive, the shell formation is normal but the cost is too high. Therefore, the addition amount is limited to 6 - 10% of the total mass.

[0050] Example 12 The difference between Example 12 and Example 1 lies in that the drug loading amount is 1% of the total mass, and the remaining conditions are exactly the same.

[0051] Example 13 The difference between Example 13 and Example 1 lies in that the drug loading amount is 20% of the total mass, and the remaining conditions are exactly the same.

[0052] Example 14 The difference between Example 14 and Example 1 lies in that the drug loading amount is 30% of the total mass, and the remaining conditions are exactly the same.

[0053] Comparative Example 11 The difference between Comparative Example 11 and Example 1 lies in that the drug loading amount is 40% of the total mass, and the remaining conditions are exactly the same.

[0054] Comparative Example 12 The difference between Comparative Example 12 and Example 1 lies in that the drug loading amount is 50% of the total mass, and the remaining conditions are exactly the same.

[0055] Table 7. Influence of the drug loading amount on the preparation in Example 1, 12 - 14 and Comparative Examples 11 - 12 Examples 1, 12 - 14 and Comparative Examples 11 - 12 explored the effect of drug loading on the preparation. The results are shown in Table 7. The main reason is that too high drug concentration will significantly increase the viscosity of the system, hinder the effective transfer of shear energy, resulting in difficulty in refining the emulsion particle size and even agglomeration. Or because at high drug loading, the surface area of drug particles increases significantly, but the dosage of emulsifier is limited by formula cost or process, resulting in that the emulsifier molecules cannot completely cover the oil - water interface, and the strength of the interfacial film is insufficient and easy to break. Therefore, the drug loading is limited to 1 - 30% of the total mass.

[0056] Example 15 The difference between Example 15 and Example 1 is that the original drug is the insecticide abamectin, and the other conditions are exactly the same.

[0057] Example 16 The difference between Example 16 and Example 1 is that the original drug is the herbicide pretilachlor, and the other conditions are exactly the same.

[0058] Table 8. Influence of the types of original drugs on the preparation in Examples 1, 15 - 16 Examples 1, 15 - 16 explored the influence of different types of original drugs on the preparation. The results are shown in Table 8, indicating that the present invention has a wide adaptability to chemical structures.

[0059] Example 17 Preparation of 10% nano - capsules of flusilazole: (1) Accurately weigh 10.52 grams of flusilazole, melt it with 10 grams of solvent oil, and the melting temperature is 45 - 60 °C. Add 4 grams of the wall material didodecyldimethylammonium chloride (DDAC) to form the oil phase. (2) Accurately weigh 1 gram of emulsifier 1600s6 and 10 grams of dispersant sodium lignosulfonate, add the remaining deionized water (make up to 100 grams), and dissolve and mix them fully and evenly at 50 °C and 300 rpm to form the water phase. (3) Start high - speed homogenization (shear rate 8000 rpm, 5 min), add the prepared oil phase to the water phase, put the homogenized emulsion into a water bath at 40 °C, adjust the stirring rate to 300 rpm, and keep it warm for 3 hours to solidify the wall material into capsules.

[0060] Example 18 Preparation of 10% pyraclostrobin nano-capsules: Accurately weigh 10.25 grams of pyraclostrobin, melt it with 10 grams of solvent oil by heating to a temperature of 65 - 80 °C, and add 3.6 grams of the wall material didecyldimethylammonium chloride (DDAC) to form the oil phase. Accurately weigh 2 grams of emulsifier 1600s6 and 8 grams of dispersant sodium lignosulfonate, add the remaining deionized water (make up to 100 grams), and dissolve and homogenize it fully and evenly at 50 °C and 300 rpm to form the aqueous phase. Start high-speed homogenization (shear rate 5000 rpm, 5 min), add the prepared oil phase to the aqueous phase, put the homogenized emulsion into a water bath at 60 °C, adjust the stirring rate to 300 rpm, and keep it warm for 1 hour to solidify the wall material into capsules.

[0061] Comparative Example 13 Using 25% pyraclostrobin emulsifiable concentrate and 40% flusilazole emulsifiable concentrate as raw materials; dilute the 25% pyraclostrobin emulsifiable concentrate with deionized water to a mass concentration of 10% and make up the volume to 10 mL to obtain dilution A; dilute the 40% flusilazole emulsifiable concentrate with deionized water to a mass concentration of 10% and make up the volume to 10 mL to obtain dilution B; mix dilution A and dilution B in a volume ratio of 3:1, make up the volume to 8 mL, and shake well to obtain the pesticide compound preparation.

[0062] Comparative Example 14 Using 40% flusilazole emulsifiable concentrate as the raw material; dilute the 40% flusilazole emulsifiable concentrate with deionized water to a mass concentration of 10% and make up the volume to 10 mL to obtain dilution B.

[0063] Comparative Example 15 Using 25% pyraclostrobin emulsifiable concentrate as the raw material; dilute the 25% pyraclostrobin emulsifiable concentrate with deionized water to a mass concentration of 10% and make up the volume to 10 mL to obtain dilution A.

[0064] Comparative Example 16 (Blank nano-capsule 1): The preparation method is the same as that of Example 1 above, but remove the drug and make up with solvent oil.

[0065] Comparative Example 17 (Blank nano-capsule 2): The preparation method is the same as that of Example 17 above, but remove the drug and make up with solvent oil.

[0066] Comparative Example 18 (Blank nano-capsule 3): The preparation method is the same as that of Example 18 above, but remove the drug and make up with solvent oil.

[0067] Comparative Example 19: Using 97% pyraclostrobin technical and 95.2% flusilazole technical as raw materials; dilute the 97% pyraclostrobin technical with methanol to a mass concentration of 10% and make up the volume to 10 mL to obtain dilution C; Dilute the 95.2% flusilazole technical with methanol to a mass concentration of 10%, and make up the volume to 10 mL to obtain dilution D; Mix dilution C and dilution D in a volume ratio of 3:1, make up the volume to 8 mL, and obtain the pesticide compound preparation after thorough shaking.

[0068] Comparative Example 20: Dilution D Comparative Example 21: Dilution C 1. Morphology characterization of different pesticide sustained-release preparations Optical imaging microscope pretreatment: Dilute each sample with deionized water, add 100 μL of the dilution to a 50 mL centrifuge tube and add 10 mL of deionized water, vortex and let stand for 30 min. After standing, suck the suspension from the upper-middle part of the centrifuge tube and titrate it onto a glass slide. Adjust the optical microscope to an appropriate brightness, observe and photograph the morphological characteristics of the nanocapsules under 50-fold magnification, such as Figure 1 As shown, the nanocapsule preparations of Examples 1-3 have uniform particle sizes and no agglomeration phenomenon.

[0069] Scanning electron microscope pretreatment: First, perform dilution, centrifugation, re-dissolution and other treatments (washing the capsules) on the nanocapsule suspension. Let the re-dissolved solution stand for 30 min, suck 1 mL of the solution from the upper-middle part, dilute it to an appropriate concentration and spot-sample it on a silicon wafer, and let it dry naturally. Photograph the morphological characteristics of the nanocapsules through a scanning electron microscope, such as Figure 2 As shown, Examples 1-3 all exhibit a typical spherical morphology, with a smooth surface and no obvious deformation or defects, indicating that the preparation process has good control ability over the basic morphology.

[0070] 2. Determination of particle sizes of different preparations Dilute each preparation with deionized water to 200 μg / mL. At room temperature, use a nanoparticle size and zeta potential analyzer from Malvern to measure the average particle size (the PI value should be less than 0.7) respectively to evaluate the size parameters of the nanocapsules. Each test is repeated three times. The results obtained are shown in Table 6 and Figure 3 As shown, for Examples 1-3, the particle sizes are 380.2 nm, 341.2 nm, and 375.1 nm respectively, and the PI value is about 0.2. The particle size distribution curve is unimodal, meeting the nanopreparation standard.

[0071] Table 9. Nanoparticle size test results 3. Determination of encapsulation performance of different preparations First, use methanol to prepare the formulations obtained in Examples 1, 17, and 18 into an initial solution (mother liquor) with a concentration of 40 ppm. Subsequently, under specific experimental conditions, namely, the volume of n-hexane is 50 mL, the volume of water is 48 mL, 2 mL of the mother liquor is added, and stirring is carried out at a rotation speed of 70 revolutions per minute. Measure the content of the technical drug at time points of 20 seconds, 30 seconds, 1 minute, and 5 minutes respectively. This step aims to determine the time required for the complete extraction of the technical drug from the system.

[0072] Once the time point for the complete extraction of the technical drug is determined, using the same method, measure the content Mt of the free drug (i.e., the unencapsulated drug) in the lignin-based nanocapsules at this time point. Here, "when the complete extraction is finished" refers to the state where the technical drug is completely extracted from the system under specific conditions, and the total amount of the drug measured at this time includes all forms (encapsulated and free) of the drug M0.

[0073] Calculate the encapsulation efficiency of the formulation according to the following formula: Encapsulation efficiency (%) = (M0 - Mt) / M0 × 100 The encapsulation efficiencies of the formulations obtained in Examples 1, 17, and 18 are as Figure 4 shown. The encapsulation efficiencies are all greater than 91, indicating that the nanocapsule system encapsulates most of the pesticide active ingredients, forms an effective physical barrier, and improves the stability of the formulation.

[0074] 4. Determination of the release performance of different formulations Dilute the formulations obtained in Examples 1, 17, and 18 and Comparative Examples 13 - 15 to 1000 μg / mL, and take 2 mL and add it to a clean and dry glass bottle (100 mL). Add a mixture of n-hexane / water (50∶50, v / v) (100 mL) to the bottle through a pipette. Immediately place the bottle on a roller, roll the bottle horizontally at 70 ± 10 r / min, and start the timer. Subsequently, aspirate 1 mL of the extraction mixture at different time intervals and immediately add the same volume of the release medium, and measure the release amount (At) of the nanocapsules at different time periods.

[0075] The measurement of A0 is carried out as follows: Dilute the formulations obtained in Examples 1, 17, and 18 and Comparative Examples 13 - 15 to 1000 μg / mL, take 2 mL and add it to a clean and dry glass bottle (100 mL), and add 48 mL of methanol. Subsequently, sonicate it with a high-power liquid crystal ultrasonic instrument at 100 Hz for 30 min. During this process, the drug encapsulated in the nanocapsules can completely diffuse into the methanol solution. Finally, aspirate the extraction mixture in the glass bottle, centrifuge it at 3000 r / min for 5 min, extract the upper layer solution, and determine the total drug content by high-performance liquid chromatography.

[0076] Cumulative release ratio (%) = At / A0×100 The test results are as follows: From Figure 5 It can be seen that the control group showed a rapid release characteristic, and the cumulative release rate reached more than 95% at 10 minutes, with no significant difference between groups; the example groups showed a significant sustained-release effect, and the cumulative release rate was 96.51% - 98.57% at 30 minutes, with no significant difference between groups; the comparison between the two groups showed that the time required for the example groups to reach the same cumulative release amount was 3 times that of the control group. In summary, the results indicate that by constructing an environmentally friendly nano-capsule drug delivery system, the release rate of the active ingredient can be effectively delayed, and this sustained-release characteristic will help to extend the effective action period of the fungicide, reduce the frequency of drug use, and thus improve the environmental friendliness of field application effects.

[0077] 5. Determination of the anti-photolysis performance of different formulations Dilute the drug-loaded formulations of Example 1, 17, 18 and Comparative Example 13 - 15 to 1000 mg / L with deionized water, and add 0.01% silicone as a wetting agent. Take 100 μL of the sample dilution and evenly apply it on a glass slide. After natural drying, place the glass slide under ultraviolet light with an average radiation intensity of 200 μW / cm2 to simulate the photolysis behavior of the carrier by ultraviolet rays. Finally, take out the glass slide and place it in a 50 mL centrifuge tube at 0 h, 0.0833 h, 0.16 h, 0.5 h, 1 h, and 2 h of photolysis. Add 10 mL of methanol to the centrifuge tube, ultrasonically treat for 30 min and then oscillate and extract for 30 min. Then take 1 mL of the supernatant and filter the impurities using a 0.22 μm organic filter membrane. Use a high-performance liquid chromatograph to measure the residual content (Mt) of the active ingredient on the glass slide at different photolysis times, and take the residual content of the active ingredient on the glass slide before photolysis as the total content (M0) to calculate the ultraviolet residual rate of the active ingredient, and thus draw the retention curve of the active ingredient of the foliar pesticide after photolysis. Calculate the pesticide residue rate of different drug-loaded formulations after photolysis according to the following formula: Pesticide residue rate (%) = Mt / M0×100% The test results are as follows: As Figure 6 shown, under the simulated sunlight irradiation conditions (light intensity: 200 μW / cm², temperature: 35°), the photolysis rate of the example groups was significantly lower than that of the control group. Specifically, after 0.17 hours of illumination, the residual rate of the active ingredient in the example groups was 43.63% - 66.27%, which was significantly higher than 33.47% - 49.73% of the control group. In summary, the environmentally friendly nano-capsule carrier can significantly improve the photostability of the active ingredient, and this improvement in photostability can enable the liquid medicine to effectively resist photolytic degradation during the retention period on the leaf surface, extend the duration of the drug effect, thereby reducing the frequency of pesticide application, reducing the amount of pesticide used and the environmental residue risk, and providing technical support for the sustainable development of agriculture.

[0078] 6. Determination of anti-scour performance of different preparations The drug-loaded preparation was diluted to 1000 mg / L with deionized water, and 0.01% silicone was added as a wetting agent. 100 μL of the sample dilution was evenly applied on the slide. After natural drying, the slide was placed on a platform 10 cm away from the burette and 30° from the horizontal plane. Finally, the slide was taken out and placed in a 50 mL centrifuge tube after flushing for 0 s, 10 s, 30 s, 60 s, 180 s, and 300 s, respectively. 10 mL of methanol was added to the centrifuge tube, and the tube was ultrasonically treated for 30 min and then oscillated for extraction for 30 min. Then 1 mL of the supernatant was taken and impurities were filtered out using an organic filter membrane with a specification of 0.22 μm. The residual content (Mt) of the active ingredient on the slide at different flushing times was determined by high performance liquid chromatography. The content of the active ingredient remaining on the slide when not flushed was taken as the total content (M0), and the UV residual rate of the active ingredient was calculated to simulate the retention curve of the active ingredient of the leaf pesticide after rainwater flushing. The pesticide residue rate after photolysis of different drug-loaded preparations was calculated according to the following formula: Pesticide residue rate (%) = Mt / M0 × 100% The test results are as follows: Figure 7 As shown, in the simulated rainwater scouring test (flow rate 60±2 rpm, angle 30°), the embodiment group showed significant anti-scouring performance advantages. Embodiment group: After 1 minute of scouring, the residual rate of the active ingredient remained at 62.15%-47.35%, and showed a slow downward trend with the extension of the scouring time. At 5 minutes, the residual amount was 41.16%-46.94%. The residual rate of the comparative example group dropped sharply to 0.34%-36.11% within 1 minute. After 5 minutes of scouring, the comparative example 2 completely fell off, while the residual rates of comparative examples 1 and 3 were 20.81% and 22.58% respectively. The study confirmed that the environmentally friendly nanocapsule preparation uses a multi-level anti-scouring mechanism (electrostatic adsorption, hydrophobic barrier, etc.) to increase the retention of active ingredients on the leaf surface compared with traditional formulations, reduce the amount of medicine, and improve the utilization rate of pesticides.

[0079] 7. Indoor antibacterial activity test The sensitivity of corn leaf blight fungus (13J) to different combinations of pesticides was determined by the mycelium growth rate method. A 5 mm bacterial disc was taken from the edge of the corn leaf blight fungus colony using a hole puncher and inoculated with an inoculation needle in the center of the drug-containing PDA plate with the mycelium side facing down. The concentration gradient of the drug-containing plate was set to 0, 0.03125, 0.0625, 0.125, 0.25, 0.5, 1, 2 L, 4, 8 and 16 μg / mL. After 7 days of dark culture at 27℃, the diameter of the colony was measured by the cross method (vertical cross method), and the growth inhibition rate and synergistic coefficient of different drug concentrations on mycelium were calculated. The formula is shown below. Each treatment was repeated three times.

[0080] Note: Analyzed by DPS software, the ordinate (Y) represents the probit value of the inhibition rate, and the abscissa (X) represents the logarithm of the agent mass concentration. The virulence regression equation Y = bx + a and the correlation coefficient R are obtained, and the EC50 value and the 95% confidence interval are calculated. The EC50 value refers to the concentration of the agent that can cause a 50% inhibitory effect on the pathogen.

[0081] The synergistic coefficient (SR) of the mixture was calculated according to the Wadley method to evaluate the synergistic effect of the mixture of agents. That is, SR > 1.5 is a synergistic effect, SR < 0.5 is an antagonistic effect, and 0.5 ≤ SR ≤ 1.5 is an additive effect.

[0082] X=(P A +P B ) / (P A / A+P B / B) SR=X / X1 Wherein, X—the theoretical value of the EC50 of the mixture, μg / mL; P A —the percentage content of A in the mixture, %; P B —the percentage content of B in the mixture, %; A—the EC 50 of A in the mixture, μg / mL; B—the EC50 of B in the mixture, μg / mL; SR—the synergistic coefficient of the mixture; X1—the measured value of the EC 50 of the mixture, μg / mL.

[0083] The test results are as follows: As shown in Table 8, the EC50 values of each group against Bipolaris maydis showed a trend of the technical group < the comparative example group < the example group < the blank nanocapsule group. In the technical group, the free technical molecules can directly and quickly play a bactericidal role, so the EC50 value is the lowest. Although the blank nanocapsule group is not loaded with drugs, the quaternary ammonium salt groups in the capsule wall material still show certain antibacterial effects, but its EC50 value is relatively high and the antibacterial effect is limited. For the conventional microcapsule preparation, due to the encapsulation of the technical, the release is restricted, resulting in an increase in the EC50 value and a weakening of the antibacterial effect. The EC50 value of the example group (environmentally friendly nanocapsule) has no significant difference from that of the comparative example group (commercial emulsifiable concentrate), which indicates that the capsule material of the environmentally friendly nanocapsule not only has antibacterial effects but also can synergistically sterilize with the technical, showing a certain synergistic effect, thus ensuring that the environmentally friendly nanocapsule has the same effect as the commercial emulsifiable concentrate. In summary, while maintaining the same effect as the commercial emulsifiable concentrate, the environmentally friendly nanocapsule preparation can reduce the loss and degradation of pesticides, thereby reducing the amount of pesticides used and environmental pollution. This helps to protect the ecological environment, improve the yield and quality of crops at the same time, and promote the sustainable development of agriculture.

[0084] Table 10. Indoor antibacterial activity test 8. Thermal stability determination Using a synchronous thermal analyzer (SDT 650, TA Instruments) combined with vacuum freeze-drying technology, the thermal protection performance of the self-assembled nanocapsules loaded with low-melting-point drugs was systematically evaluated. The experimental samples included the example groups (1, 17, 18) and the original drug powders (comparative examples 19 - 21). After the drug-loaded samples were diluted (5000 μg / mL) and mixed with deionized water at a ratio of 1:3, they were pre-frozen at -80 °C for 12 hours, and then dried samples were obtained by vacuum freeze-drying for 48 hours. 0.8 g (±0.001 g) of the dried sample was accurately weighed using an alumina crucible and placed in a nitrogen atmosphere (50 mL / min). First, it was kept at a constant temperature of 50 °C for 20 minutes, and then the temperature was raised from 50 °C to 850 °C at a heating rate of 10 °C / min.

[0085] The test results are as follows: As Figure 8 shown, the original drugs in the examples were all low-melting-point drugs, and they rapidly degraded by 44.312%, 39.186%, and 94.241% respectively in the temperature ranges of 136.63 °C - 292.65 °C, 174.01 °C - 286.98 °C, and 150.68 °C - 290.62 °C, and the DTA degradation curves were single peaks, indicating that the low-melting-point drugs had poor thermal stability. It was found through analysis that the mass curve of the self-assembled nanocapsules changed gently and the DTA degradation curve was a double peak, and the thermal stability was improved compared with the original drug. In summary, the mass of the directly exposed pesticide active ingredients under high-temperature conditions decreased significantly in a short time, and the self-assembled nanocapsules reduced the drug loss, indicating that they played a good thermal protection role for the internal pesticide components.

Claims

1. A preparation method of an environmentally friendly nanocapsule loaded with a low melting point drug, characterized in that, It includes the following steps: Weigh the drug, add solvent oil, heat to melt, add the wall material didecyldimethylammonium chloride to form the oil phase; Weigh the emulsifier and dispersant, add deionized water, heat and stir until fully and evenly dissolved to form the water phase; Add the prepared oil phase to the water phase, perform high-speed shearing and homogenization, heat the homogenized emulsion in a water bath, adjust the stirring rate to 300 r / min, and keep it warm for 2 hours to solidify the wall material into capsules.

2. The preparation method of the environmentally friendly nanocapsules loaded with low melting point drugs according to claim 1, characterized in that, The drug is a low-melting-point drug and is one of fungicides, insecticides, and herbicides.

3. The preparation method of the environmentally friendly nanocapsules loaded with low melting point drugs according to claim 1, characterized in that, The temperature for heating and melting the solvent oil is 40 - 70 °C.

4. The preparation method of the environmentally friendly nanocapsules loaded with low melting point drugs according to claim 1, characterized in that, The mass ratio of the technical drug to the solvent oil is 1:(1 - 1.5).

5. The preparation method of the environmentally friendly nanocapsules loaded with low melting point drugs according to claim 1, characterized in that, The addition amount of didecyldimethylammonium chloride (DDAC) is 2.4% - 4% of the total mass.

6. The preparation method of the environmentally friendly nanocapsules loaded with low melting point drugs according to claim 1, characterized in that, The emulsifier selected is 1600s6, and the addition amount is 1% - 4% of the total mass.

7. The preparation method of the environmentally friendly nanocapsules loaded with low melting point drugs according to claim 1, characterized in that, The dispersant selected is sodium lignosulfonate, and the addition amount is 6% - 10% of the total mass.

8. The preparation method of the environmentally friendly nanocapsules loaded with low melting point drugs according to claim 1, characterized in that, The shearing rate is 5000 - 12000 r / min, and the shearing time is 3 - 5 min.

9. The preparation method of the environment-friendly nanocapsules loaded with low-melting-point drugs according to claim 1, characterized in that, The water bath temperature is maintained at 40 - 60 °C.

10. An environmentally friendly nanocapsule loaded with a low melting point drug prepared by the preparation method according to any one of claims 1-9, characterized in that: The drug loading of the nano-capsules is 1% - 30%.

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