A lignin-based multiple emulsion fertilizer slow-release system and a preparation method thereof

Abstract

This invention belongs to the field of agricultural fertilizer and pesticide technology, specifically relating to a lignin-based multiple emulsion fertilizer and pesticide slow-release system and its preparation method. The invention involves mixing an aqueous dispersion system of alkali lignin with an oil phase containing abamectin, followed by emulsification. The resulting AVM@PE1 emulsion, an alkali lignin-aqueous dispersion system containing water-soluble fertilizer, and a second polar organic solvent containing a first surfactant are mixed and subjected to a first vortex. The resulting water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture is then mixed with an aqueous solution containing a second surfactant and subjected to a second vortex, resulting in a lignin-based multiple emulsion fertilizer and pesticide slow-release system. The lignin-based multiple emulsion fertilizer and pesticide slow-release system prepared by this invention can simultaneously encapsulate both hydrophilic and hydrophobic fertilizers and pesticides, achieving slow release and precise targeted delivery, reducing runoff and environmental pollution, and realizing synergistic effects between fertilizers and pesticides.

Description

Technical Field

[0001] This invention belongs to the field of agricultural fertilizer and pesticide technology, specifically relating to a lignin-based multiple emulsion fertilizer and pesticide slow-release system and its preparation method. Background Technology

[0002] Current agricultural productivity largely depends on the use of chemical fertilizers. However, traditional fertilizers have low nutrient utilization efficiency and fertilizer runoff pollutes the environment. Foliar precision fertilization can effectively provide nutrients to crops and significantly reduce the amount of chemical fertilizers used. However, existing foliar fertilizers suffer from poor adhesion and ineffective fertilizer application. Nanomaterials have advantages such as small size, high interfacial activity, and large specific surface area. Therefore, incorporating nanotechnology into the design of novel fertilizers holds promise for achieving efficient nutrient delivery on crop leaves. Furthermore, pesticides play a crucial role in combating biological disasters and improving crop productivity. Most pesticides are highly lipid-soluble, and the excessive use of these organic solvents poses a threat to the environment and human health. In addition, after spraying, spraying, and rain leaching, the actual utilization rate of pesticides is often less than 40%. The emergence of nanotechnology also offers hope for the efficient utilization of pesticides.

[0003] The "two-in-one" fertilizer-pesticide combination is a perfect blend of balanced fertilization and plant protection, simultaneously addressing the problem of low fertilizer and pesticide utilization rates. Functionally, the combination of fertilizer and pesticide can mutually enhance each other's effectiveness; operationally, it is time-saving, labor-saving, safe, and convenient; economically, it can reduce input costs. Therefore, this strategy will undoubtedly have a positive and fundamental promoting effect on the "dual control and two reductions" of chemical fertilizers and pesticides. However, because most fertilizers are highly water-soluble while pesticides are highly fat-soluble, developing a system that can simultaneously control the release of fertilizer and pesticides is quite challenging, and currently, there is little research on fertilizer-pesticide carriers both domestically and internationally. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a lignin-based multiple emulsion fertilizer-pesticide slow-release system and its preparation method. The lignin-based multiple emulsion fertilizer-pesticide slow-release system prepared by the present invention can simultaneously encapsulate hydrophilic and hydrophobic fertilizers and pesticides, realize the slow release and precise target delivery of fertilizers and pesticides, reduce loss and environmental pollution, and achieve synergistic effect of fertilizers and pesticides.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing a lignin-based multiple emulsion fertilizer-pesticide sustained-release system, comprising the following steps: After dispersing alkali lignin in water, the resulting suspension was filtered and the pH was adjusted to 3.0±0.1 to obtain an aqueous dispersion system of alkali lignin. Abamectin was dissolved in a first polar organic solvent to obtain an oil phase containing abamectin. The aqueous dispersion system of the alkali lignin was mixed with the oil phase containing abamectin and emulsified to obtain AVM@PE1 emulsion. The AVM@PE1 emulsion, the alkali lignin-water dispersion system containing water-soluble fertilizer, and the second polar organic solvent containing the first surfactant are mixed and subjected to a first vortex to obtain a water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture system. The water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture system is mixed with an aqueous solution containing a second surfactant and subjected to a second vortex to obtain a lignin-based multiple emulsion fertilizer-pesticide slow-release system.

[0006] Preferably, the first polar organic solvent and the second polar organic solvent independently comprise cyclohexane and / or toluene.

[0007] Preferably, the concentration of alkali lignin in the aqueous dispersion system is 0.05~1.0wt%; and the concentration of abamectin in the oil phase containing abamectin is 6~50g / L.

[0008] Preferably, the volume ratio of the aqueous dispersion system of alkali lignin to the oil phase containing abamectin is 3~5:1.

[0009] Preferably, the emulsification process is carried out at a rotation speed of 10,000 to 20,000 rpm, a time of 1 to 5 minutes, and a temperature of 15 to 35°C.

[0010] Preferably, the concentration of the water-soluble fertilizer in the alkali lignin-water dispersion system containing the water-soluble fertilizer is 100~200g / L; the water-soluble fertilizer includes one or more of urea, potassium dihydrogen phosphate, potassium nitrate, calcium nitrate, magnesium chloride, amino acids and humic acid.

[0011] Preferably, the rotational speed of the first vortex is 1000~3000 rpm, the duration is 0.5~3 min, and the temperature is 15~35℃.

[0012] Preferably, the second surfactant is one or more of Tween 20, Tween 40, and Tween 60.

[0013] Preferably, the concentration of the second surfactant in the aqueous solution containing the second surfactant is 0.25~0.75wt%.

[0014] The present invention also provides a lignin-based multiple emulsion fertilizer-pesticide sustained-release system prepared by the preparation method described in the above technical solution.

[0015] This invention provides a method for preparing a lignin-based multiple emulsion fertilizer-pesticide sustained-release system, comprising the following steps: After dispersing alkali lignin in water, the resulting suspension was filtered and the pH was adjusted to 3.0±0.1 to obtain an aqueous dispersion system of alkali lignin. Abamectin was dissolved in a first polar organic solvent to obtain an oil phase containing abamectin. The aqueous dispersion system of the alkali lignin was mixed with the oil phase containing abamectin and emulsified to obtain AVM@PE1 emulsion. The AVM@PE1 emulsion, the alkali lignin-water dispersion system containing water-soluble fertilizer, and the second polar organic solvent containing the first surfactant are mixed and subjected to a first vortex to obtain a water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture system. The water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture system is mixed with an aqueous solution containing a second surfactant and subjected to a second vortex to obtain a lignin-based multiple emulsion fertilizer-pesticide slow-release system.

[0016] Beneficial effects: This invention employs a continuous emulsification method, using natural lignin as an emulsifier to construct a multi-emulsion system capable of simultaneously encapsulating both hydrophilic and hydrophobic pesticides and fertilizers. The process is stable and easily scaled up. The resulting emulsion has a regular structure and good storage stability. Lignin endows the system with excellent biocompatibility and biodegradability. Furthermore, by controlling particle size and interfacial properties, the slow release and precise target delivery of pesticides and fertilizers can be achieved, reducing loss and environmental pollution. This results in synergistic effects between pesticides and fertilizers, exhibiting outstanding advantages of being green, environmentally friendly, highly efficient, and low-consumption. Attached Figure Description

[0017] Figure 1 The effect of AL particle concentration on PE1 (scale bar = 10µm). Figure 2 The effect of homogeneous velocity on PE1 (scale bar = 50µm). Figure 3 The effect of homogenization time on PE1 (scale bar = 20µm). Figure 4 The effect of eddy current velocity on PE2 is shown in the diagram (scale bar = 200µm). Figure 5 A schematic diagram of O / W / O / W type KH2PO4 / AVM@PE3; Figure 6 The effect of Tween 40 on PE3 (scale bar = 200µm). Figure 7 Release curves of KH2PO4 in CK and KH2PO4 / AVM@PE3; Figure 8 Release curves of AVM in CK and KH2PO4 / AVM@PE3; Figure 9Photodegradation curves of CK (AVM technical), commercial AVM formulation, and AVM in KH2PO4 / AVM@PE3 under ultraviolet irradiation. Detailed Implementation

[0018] This invention provides a method for preparing a lignin-based multiple emulsion fertilizer-pesticide sustained-release system, comprising the following steps: After dispersing alkali lignin in water, the resulting suspension was filtered and the pH was adjusted to 3.0±0.1 to obtain an aqueous dispersion system of alkali lignin. Abamectin was dissolved in a first polar organic solvent to obtain an oil phase containing abamectin. The aqueous dispersion system of the alkali lignin was mixed with the oil phase containing abamectin and emulsified to obtain AVM@PE1 emulsion. The AVM@PE1 emulsion, the alkali lignin-water dispersion system containing water-soluble fertilizer, and the second polar organic solvent containing the first surfactant are mixed and subjected to a first vortex to obtain a water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture system. The water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture system is mixed with an aqueous solution containing a second surfactant and subjected to a second vortex to obtain a lignin-based multiple emulsion fertilizer-pesticide slow-release system.

[0019] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0020] In this invention, alkali lignin is dispersed in water, and the resulting suspension is filtered and the pH value is adjusted to 3.0±0.1 to obtain an aqueous dispersion system of alkali lignin.

[0021] In one embodiment, the mass ratio of alkali lignin (AL) to water is 0.5~1:100~500, specifically 0.5:100; the water is deionized water; the dispersion is carried out under stirring conditions; the stirring time is 10~30 min, specifically 20~30 min; the stirring temperature is 10~35℃, specifically 25℃; the stirring equipment is a magnetic stirrer; the present invention does not specifically limit the filtration process, and a well-known filtration process can be used to remove undissolved residues in the suspension; the reagent used to adjust the pH value is hydrochloric acid solution; the concentration of the hydrochloric acid solution is 0.05~0.1 mol / L, specifically 0.1 mol / L.

[0022] After the alkali lignin is dissolved, it is regenerated into particles under acidic conditions to obtain a picking emulsion.

[0023] The present invention dissolves avermectin in a first polar organic solvent to obtain an oil phase containing avermectin.

[0024] In one embodiment, the first polar organic solvent includes cyclohexane and / or toluene, with cyclohexane being used in a specific embodiment; the concentration of abamectin (AVM) in the oil phase containing abamectin is 6~50 g / L, with 6~10 g / L being used in a specific embodiment; the present invention does not specifically limit the dissolution process, and a dissolution process well known in the art can be used.

[0025] After obtaining the aqueous dispersion system of the alkali lignin and the oil phase containing abamectin, the present invention mixes the aqueous dispersion system of the alkali lignin and the oil phase containing abamectin and performs emulsification treatment to obtain AVM@PE1 emulsion.

[0026] In one embodiment, the concentration of alkali lignin in the aqueous dispersion system is 0.05~1.0wt%, specifically 0.05wt%, 0.1wt%, 0.5wt%, or 1.0wt% in the embodiments; the volume ratio of the aqueous dispersion system of alkali lignin to the oil phase containing abamectin is 3~5:1, specifically 4:1 in the embodiments; the equipment used for the emulsification treatment is a homogenizer, specifically a BRT-25w high-pressure homogenizer (China) in the embodiments; the rotation speed of the emulsification treatment is 10000~20000rpm, specifically 10000, 15000, or 20000rpm in the embodiments, the time is 1~5min, specifically 1, 2, or 4min in the embodiments, and the temperature is 15~35℃, specifically 20~25℃ in the embodiments.

[0027] After obtaining the AVM@PE1 emulsion, the present invention mixes the AVM@PE1 emulsion, an alkali lignin-water dispersion system containing water-soluble fertilizer, and a second polar organic solvent containing a first surfactant, and performs a first vortex to obtain a water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture system.

[0028] In one implementation method, before mixing, the process further includes: vertically placing the AVM@PE1 emulsion on a sample stage and allowing it to separate into phases under gravity; the resulting upper phase is then mixed with an alkali lignin-water dispersion system containing water-soluble fertilizer and a second polar organic solvent; the phase separation time is 3-5 minutes, specifically 5 minutes in this embodiment. During gravity stratification, Pickering emulsion droplets accumulate in the upper phase region of the centrifuge tube due to their lower density. Static phase separation allows the emulsions to concentrate together.

[0029] In one embodiment, the water-soluble fertilizer includes one or more of urea, potassium dihydrogen phosphate, potassium nitrate, calcium nitrate, magnesium chloride, amino acids, and humic acid, with potassium dihydrogen phosphate (KH2PO4) being a specific example. The preparation method of the alkali lignin-water dispersion system containing the water-soluble fertilizer is as follows: the water-soluble fertilizer is added to the alkali lignin-water dispersion system for dissolution. The concentration of the water-soluble fertilizer in the alkali lignin-water dispersion system is 100~200g / L, with 100g / L being a specific example. The volume ratio of the AVM@PE1 emulsion to the alkali lignin-water dispersion system containing the water-soluble fertilizer is 1~2:1~2, with 1:1, 1:2, or 2:1 being a specific example.

[0030] In one embodiment, the first surfactant is one or more of Span 40, Span 60 and Span 80, and in a specific embodiment it is Span 60; the HLB of the Span 60 is 4.7; the concentration of the first surfactant in the second polar organic solvent containing the first surfactant is 0.1~1.0wt%, and in a specific embodiment it is 0.5wt.

[0031] In one embodiment, the second polar organic solvent includes cyclohexane and / or toluene, with toluene being the most specific example. The present invention does not impose a particular limitation on the volume of the second polar organic solvent; the volume of the second polar organic solvent simply needs to be in excess of the volume of the AVM@PE1 emulsion.

[0032] In one embodiment, the mixing involves mixing the AVM@PE1 emulsion with an alkali lignin-water dispersion system containing KH2PO4 and then injecting it into a second polar organic solvent.

[0033] In one implementation, the rotational speed of the first vortex is 1000~3000 rpm, specifically 1000, 2000 or 3000 rpm, the time is 0.5~3 min, specifically 1~2 min, and the temperature is 15~35℃, specifically 20~25℃; the equipment used for the first vortex is a VORTEX-GENIE 2 type vortex mixer (USA).

[0034] After obtaining the water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture system, the present invention mixes the water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture system with an aqueous solution containing a second surfactant and performs a second vortex to obtain a lignin-based multiple emulsion fertilizer-pesticide slow-release system.

[0035] In one embodiment, the second surfactant is Tween 20, Tween 40, or Tween 60. One or more of 60), specifically Tween 40 in this embodiment; the HLB of Tween 40 is 15.6, and the HLB value is the hydrophilic-lipophilic balance value; the concentration of the second surfactant in the aqueous solution containing the second surfactant is 0.25~0.75wt%, specifically 0.25wt% in this embodiment; the mixing is to vertically inject the water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture into the aqueous solution containing the second surfactant; the volume ratio of the water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture to the aqueous solution containing the second surfactant is 1:2~4, specifically 1:2, 1:3 or 1:4 in this embodiment; the present invention does not have a special limitation on the volume of the aqueous solution containing the second surfactant, it can be in excess of the water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture; the rotation speed of the second vortex is 1000~3000rpm, specifically 2000rpm in this embodiment, the temperature is 15~35℃, specifically 20~25℃ in this embodiment, and the time is 0.5~3min, specifically 0.5~1min in this embodiment.

[0036] This invention employs a continuous emulsification method, using natural lignin as an emulsifier to construct a multi-emulsion system, resulting in an emulsion with a regular structure and good stability. This system utilizes the multiphase structure of the multi-emulsion to simultaneously encapsulate both hydrophilic and hydrophobic active ingredients of pesticides and fertilizers, achieving integrated loading of pesticides and fertilizers with different properties. Simultaneously, lignin possesses excellent biocompatibility, biodegradability, and pH and laccase responsiveness, enabling slow-release and controlled-release of the encapsulated pesticides and fertilizers, as well as precise targeted delivery. This effectively improves the utilization efficiency of pesticides and fertilizers at the target sites on plants, reduces loss and environmental pollution, and promotes synergistic effects between pesticides and fertilizers. It boasts outstanding advantages such as being green and environmentally friendly, easy to operate, and highly efficient in application.

[0037] The present invention also provides a lignin-based multiple emulsion fertilizer-pesticide sustained-release system prepared by the preparation method described in the above technical solution.

[0038] In one embodiment, the lignin-based multiple emulsion fertilizer slow-release system includes water and second polar organic solvent droplets dispersed in the water; first alkali lignin particle droplets are dispersed in the second polar organic solvent droplets; the first alkali lignin particle droplets encapsulate a water-soluble fertilizer aqueous solution and droplets of abamectin and the first polar organic solvent encapsulated by the alkali lignin particles.

[0039] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0040] Example 1 Preparation of O / W (oil-in-water) Pickering emulsion AVM@PE1: Accurately weigh 0.5 g of AL powder into 100 mL of deionized water, and continuously stir with a magnetic stirrer at 25 °C for 30 min to ensure thorough dispersion. Filter the resulting suspension to remove undissolved residues, and then adjust the pH of the system to 3.0 ± 0.1 using 0.1 mol / L hydrochloric acid solution to obtain a stable aqueous dispersion of AL nanoparticles. In the emulsion preparation process, cyclohexane, a polar organic solvent, was selected as the oil phase. In standard operation, the aqueous phase (AL nanoparticle aqueous dispersion system) and the oil phase were added to a 10 mL centrifuge tube at a volume ratio of 4:1 (total volume 5 mL). Emulsification was performed using a BRT-25w high-pressure homogenizer (China) at 25 °C. The effects of rotation speed (10000, 15000, 20000 rpm) and homogenization time (1, 2, 4 min) on the emulsion were investigated. The resulting emulsion was named PE1.

[0041] When the emulsification process is carried out at a speed of 15,000 rpm for 2 minutes, and the oil phase contains 10 g / L of AVM active ingredient, the resulting emulsion is named AVM@PE1.

[0042] An initial 5 wt% AL nanoparticle aqueous dispersion system was prepared. After pH adjustment, the AL concentration was adjusted to a series of gradients: 0.05 wt%, 0.1 wt%, 0.5 wt%, and 1.0 wt%. PE1 emulsions were prepared from these concentration gradient samples using the aforementioned method to study the relationship between the concentration of the solid emulsifier (alkali lignin particles) and the stability of the emulsion.

[0043] Figure 1 The effect of AL particle concentration on PE1 is shown in the figure (scale bar = 10µm).

[0044] from Figure 1 As can be seen, within the above concentration range, AL particles can effectively stabilize O / W type Pickering emulsions. When the AL particle concentration is low (0.05 wt%), the average droplet diameter of the emulsion can reach 25.54 μm. As the particle concentration increases to 1 wt%, the droplet diameter decreases significantly to 8.39 μm. This may be because, under low concentration conditions, the limited number of AL particles cannot completely cover the oil / water interface, resulting in a high interfacial energy per unit area. The system reduces the total interfacial energy by forming large droplets (low specific surface area). However, when the particle concentration increases, more particles can adsorb to the interface to form a dense protective layer, enabling the system to maintain a smaller droplet size.

[0045] Figure 2 The graph shows the effect of homogeneous velocity on PE1 (scale bar = 50µm).

[0046] In the Pickering emulsion preparation process, the homogenizer speed is also one of the key factors affecting the emulsion morphology. From Figure 2 It can be clearly observed that when the homogenizer speed is 10,000 rpm, the prepared emulsion exhibits a relatively large droplet size, with the maximum measured droplet size reaching 49.66 μm. However, when the homogenizer speed is significantly increased to 20,000 rpm, the average droplet size of the emulsion decreases significantly to only 23.03 μm. Under low-speed operation, the aqueous and oil phases are difficult to mix fully and efficiently, resulting in the oil phase not being uniformly dispersed in the system, ultimately leading to larger droplet sizes. High speed, on the other hand, brings stronger shear forces to the system, allowing the oil phase to be fully broken down and dispersed under this strong force, resulting in a finer emulsion structure and a significantly smaller droplet size.

[0047] Figure 3 The effect of homogenization time on PE1 is shown in the figure (scale bar = 20µm).

[0048] Figure 3 The changes in Pickering emulsions under different homogenization times are shown. When the homogenization time is only 1 min, an O / W structured emulsion can be prepared, and the surface AL nanoparticles exhibit excellent emulsifying properties, with an average droplet size of 27.52 μm. However, when the homogenization time is extended to 2 min, the emulsion droplet size decreases significantly. This may be because the further extension of the shear time allows the oil phase to distribute with higher dispersion, leading to the adsorption of more AL nanoparticles at the water / oil interface, ultimately resulting in smaller droplet size. When the homogenization time is extended to 4 min, the emulsion droplet size shows a slight increase. This phenomenon may be due to the continuous disruption and subsequent rearrangement of the originally ordered AL particles at the water-oil interface under high-speed homogenization conditions. This dynamic process disturbs the stability of the emulsion system, thus causing a slight increase in droplet size.

[0049] Example 2 Preparation of W / O / W (water-in-oil-in-water) emulsion KH2PO4 / AVM@PE2: The prepared AVM@PE1 emulsion was placed vertically on the sample stage and subjected to phase separation for 5 minutes under gravity. During this time, the Pickering emulsion droplets, due to their lower density, accumulated in the upper phase region of the centrifuge tube. 1.0 ± 0.1 mL of the emulsion (upper phase region) was precisely transferred using a pipette, taking care to prevent contamination of the bottom continuous phase during sampling. This emulsion phase was then rapidly introduced into an excess of cyclohexane stabilizing system containing 0.5 wt% Span 60 (HLB = 4.7). Subsequently, a VORTEX-GENIE 2 vortex mixer (USA) was used for vortexing at 25°C for 1 minute at speeds of 1000, 2000, and 3000 rpm to obtain the W / O / W type emulsion PE2.

[0050] To achieve co-loading of dual active ingredients, an aqueous phase containing 100 g / L KH2PO4 (0.5 wt% AL dispersion) and AVM@PE1 emulsion were mixed at a preset volume ratio of 1:1, and then an excess (compared to AVM@PE1 emulsion) of toluene system (containing 0.5 wt% Span 60, HLB=4.7) was injected. After vortexing at 2000 rpm for 1 min at 25°C, a KH2PO4 / AVM@PE2 fertilizer-pesticide mixture was obtained.

[0051] Figure 4 The diagram shows the effect of eddy current velocity on PE2 (scale bar = 200µm).

[0052] like Figure 4 As shown, the rotational speed of the eddy has a significant impact on the dispersibility of the generated PE2. When the eddy speed is 1000 rpm, the resulting emulsion has a larger size, with an average bubble diameter of 288.51 µm. Larger bubbles experience higher interfacial tension and lower stability, making them more susceptible to rupture under environmental disturbances, thus weakening the protective effect on the active ingredients. When the eddy speed is 2000 rpm, the resulting emulsion has a more regular shape, with an average bubble diameter of 171.29 µm. When the eddy speed reaches 3000 rpm, the average particle size is 102.31 µm. These phenomena indicate that as the eddy speed increases, the shear force on the emulsion droplets also increases, thereby improving dispersibility.

[0053] Example 3 Preparation of O / W / O / W (oil-in-water emulsion) KH2PO4 / AVM@PE3 emulsion: Aqueous systems are more environmentally friendly than oil-phase systems. Therefore, the W / O / W type emulsion PE2 was precisely introduced into an aqueous system containing gradient concentrations of Tween 40 (HLB=15.6) to construct a three-stage emulsion structure with environmentally friendly characteristics. The specific procedure is as follows: 1.0 mL of PE2 was quantitatively transferred and vertically injected into deionized water containing an excess of Tween 40 surfactant (0.25 wt%, 0.50 wt%, 0.75 wt%). After vortexing at 2000 rpm for 30 seconds at 25°C, an O / W / O / W type emulsion PE3 was formed.

[0054] When the system contains dual active ingredients of KH2PO4 and AVM, it is named KH2PO4 / AVM@PE3 drug-loaded system. The specific steps are as follows: 1.0 mL of the KH2PO4 / AVM@PE2 drug-fertilizer mixture is quantitatively transferred and vertically injected into deionized water containing an excess of Tween 40 (0.25 wt%) surfactant, and vortexed at 2000 rpm for 30 s at 25°C.

[0055] Figure 5 This is a schematic diagram of O / W / O / W type KH2PO4 / AVM@PE3.

[0056] Figure 6 The effect of Tween 40 on PE3 is shown in the figure (scale bar = 200µm).

[0057] Aqueous systems are more environmentally friendly than oil-phase systems. Therefore, the prepared PE2 was redispersed in deionized water containing the aqueous surfactant Tween 40 to form O / W / O / W type PE3 (such as...). Figure 5 ).like Figure 6 As shown, the concentration of Tween 40 significantly affects the microstructure of PE3. When the concentration of Tween 40 is 0.25 wt%, the success rate of PE3 preparation is relatively high. However, under other concentration conditions, abnormal phenomena such as demulsification and poor dispersibility occur.

[0058] Performance testing (1) Sustained-release performance of KH2PO4 / AVM@PE3 To investigate the sustained-release performance of this system, the experiment included two comparative systems: a control group (1 mL AVM + 1 mL KH₂PO₄) and an experimental group (2 mL KH₂PO₄ / AVM@PE₃). Each sample was added to 28 mL of ethanol solution (50 vol%), then transferred to a dialysis bag, vertically immersed in a 500 mL glass bottle, and 270 mL of the release medium ethanol solution (50 vol%) was added, maintaining a total volume of 300 mL. The glass bottles were placed in a shaking incubator at a constant temperature of 25°C and a shaking rate of 200 rpm. At regular intervals, 1 mL of the sustained-release solution was taken out, and the concentration of AVM was determined by high-performance liquid chromatography (HPLC), and the concentration of potassium ions was determined by flame photometry. Simultaneously, 1 mL of ethanol solution (50 vol%) was added to ensure a consistent sustained-release volume.

[0059] Figure 7 The graphs show the release curves of KH2PO4 in CK and KH2PO4 / AVM@PE3. Figure 8 Release curves of AVM in CK and KH2PO4 / AVM@PE3.

[0060] The release curve of KH2PO4 is as follows: Figure 7 As shown, the release curve of the CK treatment has a steeper slope in the initial stage, indicating rapid release at this stage. In contrast, the KH2PO4 / AVM@PE3 treatment shows a slower release in the initial stage, indicating a significant sustained-release effect of the multiple emulsions. The CK treatment reached nearly 80% release after 50 hours and exceeded 93% after 200 hours. However, the KH2PO4 / AVM@PE3 treatment only reached 60% release after 150 hours, and the release rate approached equilibrium at only 78% after 250 hours. This demonstrates that loading KH2PO4 into the multiple emulsion KH2PO4 / AVM@PE3 can significantly slow down the release rate of KH2PO4, avoiding nutrient loss or short-term concentration overload caused by rapid release.

[0061] AVM, a macrolide antibiotic insecticide, is highly sensitive to light and easily becomes inactive through photolysis upon exposure to the environment, resulting in low drug utilization. Figure 8 As shown, the AVM released in the KH2PO4 / AVM@PE3 treatment was only about 20% after 50 hours, and entered a release plateau after 150 hours, with a final release rate of about 70%. This indicates that the AVM in KH2PO4 / AVM@PE3 can exert its effect for a long time, reducing the phytotoxicity caused by burst release. Furthermore, the release rate of AVM in KH2PO4 / AVM@PE3 is slower than that of KH2PO4. For example, after 50 hours of sustained release, the release rate of KH2PO4 was 31%, while the release rate of AVM was 22.30%. This is because the AVM is encapsulated in the oil in PE1, which provides an additional protective layer compared to KH2PO4 encapsulated in PE2.

[0062] (2) Photolysis resistance of KH2PO4 / AVM@PE3 To evaluate the photodegradation resistance of AVM in the drug-loaded system, specific amounts of KH₂PO₄ / AVM@PE₃, commercial AVM emulsion, and AVM ethanol solution (CK) were added to 4.0 cm diameter glass culture dishes. The dishes were then placed under UV light (40W, 340 nm) at a distance of 40 cm at room temperature for 0, 3, 6, 12, 24, 36, 48, 60, and 96 h. After UV irradiation, the remaining AVM content in each culture dish was extracted by ultrasonication with an ethanol / water (50 / 50, v / v) solution, filtered through a 0.22 μm organic filter membrane, and analyzed by HPLC. Each treatment was repeated three times.

[0063] Figure 9 Photodegradation curves of CK (AVM technical), commercial AVM formulation, and AVM in KH2PO4 / AVM@PE3 under ultraviolet irradiation.

[0064] like Figure 9 As shown, under ultraviolet irradiation, the photolysis rate of AVM technical material is very fast. After 12 hours of irradiation, only 47.12% of the active ingredient remains. Therefore, improving the UV resistance of AVM is an urgent problem to be solved in its practical application. Commercial AVM emulsions contain some organic components, which can endow them with certain UV resistance, but the effect is not ideal. After 12 hours of UV irradiation, the AVM decomposition rate of commercial AVM emulsions exceeds 40%. In the KH2PO4 / AVM@PE3 system designed in this invention, the photolysis rate of AVM is relatively slow, which is due to the UV absorption capacity of AL, allowing the active ingredient to still reach 55% after 96 hours of UV irradiation.

[0065] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a lignin-based multiple emulsion fertilizer-pesticide sustained-release system, characterized in that, Includes the following steps: After dispersing alkali lignin in water, the resulting suspension was filtered and the pH was adjusted to 3.0±0.1 to obtain an aqueous dispersion system of alkali lignin. Abamectin was dissolved in a first polar organic solvent to obtain an oil phase containing abamectin. The aqueous dispersion system of the alkali lignin was mixed with the oil phase containing abamectin and emulsified to obtain AVM@PE1 emulsion. The AVM@PE1 emulsion, the alkali lignin-water dispersion system containing water-soluble fertilizer, and the second polar organic solvent containing the first surfactant are mixed and subjected to a first vortex to obtain a water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture system. The water-soluble fertilizer / AVM@PE2 fertilizer-pesticide mixture system is mixed with an aqueous solution containing a second surfactant and subjected to a second vortex to obtain a lignin-based multiple emulsion fertilizer-pesticide slow-release system.

2. The preparation method according to claim 1, characterized in that, The first polar organic solvent and the second polar organic solvent independently include cyclohexane and / or toluene.

3. The preparation method according to claim 1, characterized in that, The concentration of alkali lignin in the aqueous dispersion system is 0.05~1.0wt%; the concentration of abamectin in the oil phase containing abamectin is 6~50g / L.

4. The preparation method according to claim 1 or 3, characterized in that, The volume ratio of the aqueous dispersion system of alkali lignin to the oil phase containing abamectin is 3~5:

1.

5. The preparation method according to claim 1, characterized in that, The emulsification process is carried out at a speed of 10,000 to 20,000 rpm, a time of 1 to 5 minutes, and a temperature of 15 to 35°C.

6. The preparation method according to claim 1, characterized in that, The concentration of water-soluble fertilizer in the alkali lignin-water dispersion system containing water-soluble fertilizer is 100~200g / L; the water-soluble fertilizer includes one or more of urea, potassium dihydrogen phosphate, potassium nitrate, calcium nitrate, magnesium chloride, amino acids and humic acid.

7. The preparation method according to claim 1, characterized in that, The rotational speed of the first vortex is 1000~3000 rpm, the duration is 0.5~3 min, and the temperature is 15~35℃.

8. The preparation method according to claim 1, characterized in that, The second surfactant is one or more of Tween 20, Tween 40 and Tween 60.

9. The preparation method according to claim 1 or 8, characterized in that, The concentration of the second surfactant in the aqueous solution containing the second surfactant is 0.25~0.75wt%.

10. The lignin-based multiple emulsion fertilizer-pesticide sustained-release system prepared by the preparation method according to any one of claims 1 to 9.

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