Preparation and Application of Lignin-based Sustained and Controlled Release Pickering Nano / Microcapsules

Abstract

The present invention discloses a preparation method of lignin-based Pickering microcapsules. Lignin nanoparticles suspension is prepared in water by modified lignin as the aqueous phase; an initiator and a crosslinking agent are dissolved in an organic solvent as the oil phase; the aqueous phase and the oil phase are mixed and emulsified to prepare an O / W type Pickering emulsion; and crosslinking and curing are carried out by heating to obtain lignin microcapsules.

Description

Technical Field

[0001] The present invention relates to a preparation method of lignin-based sustained-release Pickering nano / microcapsules and their application in pesticide carriers. Background Art

[0002] Pesticides are important agricultural production materials. For a long time, the development and application of chemical pesticides have played an irreplaceable and important role in effectively controlling pesticide pests and diseases in a timely manner and ensuring high yields and increased production of agricultural products, greatly promoting the development of agriculture. However, during the spraying process, pesticides are easily washed away by rainwater and lost in large amounts into the environment, resulting in a short pesticide persistence period and low effective utilization rate. The active ingredients of pesticides in the environment are easily degraded, affecting the control effect. To achieve good control effects, pesticides must be sprayed multiple times and in large quantities, consuming a large amount of manpower, material resources and financial resources, and also causing harm to the ecological environment.

[0003] Therefore, using cutting-edge modern technology means to develop advanced pesticide formulation processing technologies, improve the effective utilization rate of pesticides, and reduce their dosage and residual pollution in non-target areas and the environment is of great significance for alleviating the current pesticide residue and environmental pollution problems in China, ensuring food production, food and ecological safety, and promoting the sustainable development of the pesticide industry.

[0004] In recent years, the rapid development of nanotechnology has provided new ideas for the development of pesticide controlled-release technology. Using nanomaterials and technologies as carriers and supports to construct nano-drug delivery systems and prepare new controlled-release nano-pesticide formulations is an effective way to overcome the defects of traditional drug formulations. In recent years, pesticide microcapsule suspensions, which are widely used, have become an important research hotspot in pesticide formulations.

[0005] Currently, the relatively mature microencapsulation process schemes at home and abroad mainly use interfacial polymerization and in-situ polymerization technologies. However, interfacial polymerization mainly uses polyurethane or polyurea as the synthetic wall material, and the wall material has a slow metabolism in the environment and is prone to accumulation after long-term use; in-situ polymerization mainly uses urea-formaldehyde resin and melamine resin, etc., which pose environmental risks due to the presence of formaldehyde. In recent years, using easily degradable polymer natural macromolecules such as alginate, gelatin, and modified cellulose and chitosan as wall materials has gradually become a research hotspot in microencapsulation [Nanomaterials, 2018, 8(10): 857; Journal of Hazardous Materials, 2021, 403: 123654]. Due to limitations such as process and cost factors, the above methods still have great limitations in the application of the pesticide industry. Finding natural products and easily degradable materials; developing microencapsulation technologies with simple processes, low costs and easy industrialization is the current research hotspot in pesticide slow-release research.

[0006] As a natural polymer material with high biocompatibility, lignin itself contains many reactive sites. Grafting or modifying different hydroxyl groups will affect the hydrophilicity and hydrophobicity of lignin molecules, and thus affect the emulsifying performance of lignin particles, thereby broadening its application scenarios. Preparing microcapsules with Pickering emulsions stabilized by lignin particles can effectively reduce the cost of the capsule wall material, improve its biodegradability, reduce the dosage of surfactants, and enhance environmental safety. In addition, since lignin molecules contain phenylpropane units and phenolic hydroxyl groups that can effectively scavenge free radicals, it has good anti-ultraviolet degradation and antioxidant properties, and can significantly improve the photostability of encapsulated pesticides. However, there are few studies on directly using modified lignin particles as emulsifiers to prepare lignin microcapsules at present.

[0007] Frederik R. Wurm reported in 2020 [ACS Sustainable Chem. Eng. 2020, 8, 18468 - 18475] that sodium lignosulfonate, a fat-soluble pesticide, and a cross-linking agent were dissolved in an organic solvent and then dispersed in an aqueous phase, and the organic solvent was removed by heating and cross-linked and solidified into nanoparticles. The drug loading rate of the nano-pesticide preparation prepared by this method was low; Luo et al. [Chemical Engineering Journal, 2020, 394: 124854.] constructed lignin microcapsules containing pyraclostrobin by interfacial polymerization of sodium lignosulfonate and isocyanate, with an average particle size of about 160 nm. However, this method still requires the addition of a large amount of emulsifier to disperse and regulate the interfacial polymerization process. In addition, the formed capsule wall is a polyurethane (PU) - like compound, containing structural fragments that are not easily degraded, and a large amount of emulsifier is still required in this preparation process, which poses a risk to the environment. Chen et al. [ACS Sustainable Chem. Eng. 2016, 4(10): 5204 - 5211] grafted allyl groups onto sodium lignosulfonate through an etherification reaction and then prepared lignin microcapsules by interfacial polymerization in a water-in-oil microemulsion system without constructing a Pickering emulsion template. In the preparation process of this material, dialysis bags need to be used for dialysis first, and a cell disruption process is used in the emulsification and encapsulation process, which requires a large power and high energy consumption and is difficult to industrialize. Therefore, it is necessary to develop a more industrially promising method for preparing lignin microcapsules.

[0008] Preparing microcapsules using the Pickering emulsion template method can improve the protection and controlled release of the core material and has broad prospects in drug loading and controlled release. Bollhors et al. reported that using Pickering emulsions with solid particles instead of traditional surfactants as emulsifiers can reduce the dosage of emulsifiers and has unique advantages such as environmental friendliness, reusability, and high stability.

[0009] Alkali lignin has been used in the preparation of microcapsule phase change carrier materials by the Pickering emulsion method, but the obtained microcapsules have a micron-sized particle size and a thick capsule wall. For example, Pang et al. [Industrial Crops & Products, 2021, 167(10): 113468] prepared lignin nanoparticles by an acid precipitation method as an emulsifier to form microcapsules on the basis of a Pickering emulsion. However, the acid precipitation method only produces pure lignin particles, which have problems such as low yield, long dialysis cycle, and difficulty in industrialization. In addition, the lignin nanoparticles are not modified, have strong hydrophilicity, and have a large lignin particle size, which will affect the emulsifying performance and form micron-sized capsules with a large particle size. Although the pesticide is encapsulated, the drug loading rate is not high.

[0010] Currently, interfacial polymerization is used to generate microcapsules, but commonly used isocyanates are used as reaction raw materials, resulting in poor degradability of the capsule wall and insufficient environmental protection. Summary of the Invention

[0011] The problem to be solved by the present invention is to provide a preparation and application of lignin-based sustained-release Pickering nano / microcapsules.

[0012] To solve the above technical problems, the present invention provides a preparation method of lignin-based sustained-release Pickering microcapsules, which successively includes the following steps:

[0013] 1), Modify lignin by an esterification reaction to graft organic alkene groups onto lignin molecules to obtain modified lignin;

[0014] 2), Dissolve the modified lignin in an organic solvent and disperse it in an aqueous solution containing a surfactant, and remove the organic solvent (remove the organic solvent by heating and evaporation) to obtain a suspension of lignin nanoparticles;

[0015] 3), Use a pesticide, an organic solvent, a crosslinking agent, and an initiator to form an oil phase, and use the suspension of lignin nanoparticles obtained in step 2) as the water phase. Mix and emulsify the water phase and the oil phase to prepare an O / W type Pickering emulsion;

[0016] 4), At a certain temperature, initiate the crosslinking polymerization of lignin particles and the crosslinking agent at the oil-water interface to form lignin microcapsules loaded with pesticides.

[0017] As an improvement of the preparation method of the lignin-based sustained-release Pickering microcapsules of the present invention, the preparation method of the modified lignin is:

[0018] Lignin is added to an aprotic polar organic solvent, and heated with stirring at 90±5 °C until the lignin is completely dissolved. After cooling to room temperature, an organic base is added, and then methacryloyl chloride is added, and heated to react to obtain modified lignin; the mass ratio of the aprotic polar organic solvent to lignin is (20-25):1; the mass ratio of the lignin, organic base, and methacryloyl chloride used is 10:(10-20):(10-20); the heating reaction is carried out at 50 °C for 15-24 h.

[0019] As a further improvement to the preparation method of the lignin-based sustained-release Pickering microcapsules of the present invention, in the preparation method of the modified lignin: the lignin is at least one of alkali lignin and lignosulfonate; the aprotic polar organic solvent is at least one of acetonitrile, dimethylformamide, and dimethyl sulfoxide; the organic base is at least one of triethylamine, N-methylmorpholine, and N,N-diisopropylethylamine.

[0020] As a further improvement to the preparation method of the lignin-based sustained-release Pickering microcapsules of the present invention, the preparation method of the lignin nanoparticle suspension is:

[0021] The modified lignin obtained in step 1) is completely dissolved in a volatile organic solvent to obtain a lignin organic solution; an aqueous solution containing a surfactant is prepared; in the surfactant aqueous solution, the mass concentration of the surfactant is 0.2-0.5%; the above-mentioned lignin organic solution is added (dropped) into the aqueous solution containing the surfactant, and stirred (rapidly stirred); heated to the temperature at which the organic solvent can volatilize, and the organic solvent is removed to obtain a lignin nanoparticle suspension; the mass ratio of the modified lignin to the volatile organic solvent is 1:(5-15); the mass ratio of the modified lignin to the surfactant is (5-10):1.

[0022] As a further improvement to the preparation method of the lignin-based sustained-release Pickering microcapsules of the present invention, in the preparation method of the lignin nanoparticle suspension:

[0023] The volatile organic solvent is at least one of acetonitrile, acetone, and dichloromethane; the surfactant is one or more of cetyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, styrenylphenol formaldehyde resin, polyoxyethylene sorbitan monooleate, polyoxyethylene polyoxypropylene block polyether, alkylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene, sulfonic esters, amides, and organosilicons.

[0024] As a further improvement to the preparation method of the lignin-based sustained-release Pickering microcapsules of the present invention, in the preparation method of the lignin Pickering emulsion:

[0025] Using the lignin nanoparticle suspension prepared in step 2) as the aqueous phase, dissolving a crosslinking agent, an initiator, and a pesticide in an organic solvent as the oil phase. After mixing the oil phase and the aqueous phase, high-shear homogenization emulsification is carried out to obtain an O / W type lignin Pickering emulsion. The mass ratio of the lignin, crosslinking agent, initiator, organic solvent of the oil phase, and pesticide used is 100:(100 - 120):(10 - 20):(500 - 1000):(100 - 1000).

[0026] As a further improvement of the preparation method of the lignin-based sustained-release Pickering microcapsules of the present invention, in the preparation method of the lignin Pickering emulsion:

[0027] The crosslinking agent is at least one of 3-mercaptopropionate, trimethylolpropane tris(3-mercaptopropionate), and trimethylolpropane triacrylate; the initiator is at least one of azobisisobutyronitrile, azobisisovaleronitrile, and azobisisoheptonitrile; the pesticide is a lipophilic pesticide; the organic solvent is at least one of 120# solvent oil, 150# solvent oil, cyclohexanone, methyl myristate, methyl palmitate, and xylene; the high-shear emulsification is carried out at 10000 - 20000 rpm for 3 - 10 min.

[0028] As a further improvement of the preparation method of the lignin-based sustained-release Pickering microcapsules of the present invention, step 4) is: heating the lignin Pickering emulsion (Pickering emulsion of O / W type) obtained in step 3) to initiate a crosslinking reaction (that is, initiating crosslinking polymerization of lignin particles and the crosslinking agent at the oil-water interface to obtain a lignin microcapsule suspension (that is, forming lignin microcapsules loaded with pesticides); the stirring speed of the heating crosslinking reaction is 200 - 500 rpm; the heating temperature is 50 - 80 °C; the reaction time is 2 - 8 h.

[0029] The present invention also simultaneously provides lignin-based sustained-release Pickering microcapsules prepared by using the above method.

[0030] The present invention overcomes problems such as high material synthesis cost and complex purification process in the prior art through a simple esterification modification process of lignin materials, and realizes the large-scale production of modified lignin materials without dialysis.

[0031] Under relatively mild conditions, the method of the present invention uses an initiator to crosslink a crosslinking agent with a large number of lignin particles adsorbed on the Pickering emulsion interface to form a continuous lignin capsule wall, and prepares high-strength lignin wall material microcapsules by a simple method. Using modified lignin particles as an emulsifier to prepare pure lignin microcapsules solves the problem of excessive use of emulsifiers in the preparation of pesticides. Specifically, lignin is first esterified and modified to graft organic alkene groups onto the lignin molecule; then, a pesticide, an organic solvent, a crosslinking agent, and an initiator are used to form an oil phase, and a lignin particle dispersion is used as the water phase. The water phase and the oil phase are mixed and emulsified to prepare an O / W type Pickering emulsion; then, at a certain temperature, the lignin particles and the crosslinking agent are caused to crosslink and polymerize at the oil-water interface to form pesticide-loaded lignin microcapsules.

[0032] Specifically, the present invention is: a method for preparing lignin-based Pickering microcapsules, which prepares a lignin nanoparticle suspension in water by modifying lignin as the water phase; dissolves a pesticide fat-soluble technical material, an initiator, and a crosslinking agent in an organic solvent as the oil phase; mixes and emulsifies the water phase and the oil phase to prepare an O / W type Pickering emulsion; and heats for crosslinking and curing to obtain lignin microcapsules.

[0033] The dosage of each component is preferably, in parts by mass: 100 parts of water; 0.1 - 1 part of surfactant; 0.1 - 1 part of lignin; 0.01 - 0.1 part of initiator; 0.1 - 1 part of crosslinking agent; 10 - 50 parts of organic solvent.

[0034] The surfactant is preferably one or more of cetyltrimethylammonium bromide, sodium dodecylbenzenesulfonate, styrenylphenol formaldehyde resin, polyoxyethylene sorbitan monooleate, polyoxyethylene polyoxypropylene block polyether, alkylphenol polyoxyethylene ether, octylphenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, fatty alcohol polyoxyethylene, sulfonic acid esters, amides, and organosilicones. The lignin may include at least one of alkali lignin and sodium lignosulfonate. The initiator may include at least one of azobisisobutyronitrile, azobisisovaleronitrile, and azobisisoheptonitrile. The crosslinking agent may include at least one of 3-mercaptopropionate, trimethylolpropane tris(3-mercaptopropionate), and trimethylolpropane triacrylate. The organic solvent may include at least one of cyclohexanone, methyl myristate, methyl palmitate, and xylene. The emulsification is preferably carried out by emulsification treatment at 10000 - 20000 rpm for 2 - 8 min. The heating crosslinking and curing is preferably carried out at a stirring speed of 200 - 500 rpm and a temperature of 50 - 80 °C for 2 - 8 h.

[0035] The preparation method specifically includes the following steps:

[0036] 1) Preparation of modified lignin

[0037] Under nitrogen protection, lignin was dissolved in a non-ionic polar organic solvent and heated for dissolution. After complete dissolution, the temperature was lowered, and triethylamine was added dropwise. Methacryloyl chloride was added dropwise, and the mixture was heated and reacted overnight. It was cooled to room temperature, poured into water for precipitation, centrifuged and separated, and the solid was dried in vacuum.

[0038] 2) Preparation of lignin nanoparticles

[0039] The above-mentioned modified lignin was completely dissolved in an organic solvent. An aqueous solution containing a surfactant was prepared. The lignin organic solution was added dropwise to the aqueous solution and stirred rapidly. After heating to volatilize the organic solvent, a lignin nanoparticle suspension was obtained.

[0040] 3) Preparation of lignin Pickering emulsion

[0041] The lignin nanoparticle suspension prepared in step (2) was used as the aqueous phase, and the lipophilic original drug, initiator, and crosslinking agent were dissolved in an organic solvent as the oil phase. After mixing the oil phase and the aqueous phase, emulsification was carried out to obtain a lignin Pickering emulsion.

[0042] 4) Preparation of lignin microcapsules

[0043] The above emulsion was heated to initiate a crosslinking reaction to obtain a lignin microcapsule suspension.

[0044] The preparation process of this method is simple, the reaction conditions are mild, the strength of the microcapsule wall prepared is high, and it can be used for encapsulating lipophilic pesticides. The lignin microcapsules of the present invention take lignin, surfactant, crosslinking agent, initiator, and organic solvent as main raw materials, and through the formation of Pickering emulsion and its interfacial crosslinking reaction, the pesticide is embedded in the lignin microcapsules.

[0045] In step 2) of the present invention, the modified lignin nanoparticles are suspended in water to form a nanoscale suspension. The size and concentration of the nanoparticles are crucial for the subsequent formation of Pickering emulsion; in step 3), the selection of the initiator and crosslinking agent and the oil phase ratio have certain effects on the formation of Pickering emulsion, the fineness of the emulsion, the stability of the emulsion, and the pesticide loading capacity; in step 4), the curing temperature, curing reaction time, and curing idea are particularly critical for the final step of forming microcapsules, which are related to the particle size and drug loading rate of the flexible capsule formed based on Pickering emulsion.

[0046] The technical advantages of the present invention are as follows: Through a simple esterification modification process of lignin materials, large-scale production of modified lignin materials is achieved without dialysis, overcoming problems such as high material synthesis cost and complex purification process in the prior art. Under relatively mild conditions, an initiator is used to crosslink a crosslinking agent with a large number of lignin particles adsorbed on the interface of Pickering emulsion to form a continuous lignin capsule wall. A lignin wall material drug-loaded nano / microcapsule with a high drug loading rate is prepared by a simple method. Using modified lignin particles as an emulsifier to prepare pure lignin microcapsules solves the problem of excessive use of emulsifiers in the preparation process of pesticides. In short, the reaction conditions of the present invention are mild, the process is simple, the operability is strong, the prepared drug-loaded nano / microcapsules have small particle sizes, can effectively control the pesticide release rate, extend the action time, and at the same time reduce environmental pollution; it can also avoid the degradation of the active ingredients of pesticides during use and improve the effective utilization rate.

[0047] In the present invention, lipophilic modified lignin nanoparticles are suspended in water as an emulsifier, first mixed with an oil phase containing a lipophilic technical material, sheared and emulsified into a Pickering emulsion, and then crosslinked and solidified to form a flexible, environmentally friendly and degradable nano-scale lignin microcapsule.

[0048] Compared with the prior art, the present invention has the following advantages:

[0049] According to the present invention, using modified lignin nanoparticles as an emulsifier, based on Pickering emulsion, crosslinked and solidified into a pesticide sustained-release nano / microcapsule, the crosslinking agent (TMPMP) is an acid-responsive crosslinking agent, which degrades slowly under acidic conditions, can effectively control the pesticide release rate, extend the action time, and at the same time reduce environmental pollution; it can also avoid the degradation of the active ingredients of pesticides during use and improve the effective utilization rate.

[0050] The present invention modifies lignin, uses it as solid dispersion particles to prepare Pickering emulsion, and uses this as a template to prepare lignin microcapsules. This preparation method has the characteristics of mild reaction conditions, simple preparation process, fast speed, low cost, no harmful additives, the synthesized carrier is degradable, and no secondary pollution, and is a preparation method suitable for industrial application.

[0051] In addition, the particle size and drug loading amount of the lignin microcapsules prepared according to the present invention are controllable, can adapt to various different spraying environments, and have considerable application prospects in the field of pesticide formulations, especially in the field of sustained-release formulations.

[0052] The organic solvent selected in the present invention is temperature-sensitive, the cross-linking agent is sensitive to acids and bases, and laccase can degrade the lignin wall material. Therefore, the release rate of the encapsulated substance can be controlled through the above conditions, that is, the microcapsules prepared in the present invention have temperature, pH and enzyme responsiveness. A large number of hindered phenol structures in the lignin molecule as the wall material are beneficial to improving the stability of photosensitive or oxygen-sensitive encapsulated objects.

[0053] The present invention provides the application of lignin microcapsules in the controlled release of pesticides, wherein the lignin microcapsules are opaque soft capsule materials with controllable sizes. In the present invention, the pesticides are conventional lipophilic pesticides, such as pyraclostrobin, difenoconazole, tebuconazole, fludioxonil, etc.

[0054] In summary, the present invention has developed a method for preparing lignin drug-loaded microcapsules with a simple process: the alkali lignin after lipophilic modification can be dispersed to form nanoparticles, which have certain hydrophilic-lipophilic properties. By adjusting the degree of esterification, the nanoparticles can be used as interfacial stabilizers to form Pickering emulsions, replacing the use of a large amount of surfactants. Further, stable drug-loaded nano / microcapsules are prepared through interfacial cross-linking and curing. Based on using the lipophilic-modified lignin nanoparticles as stabilizers to stabilize the oil-water interface of lipophilic active ingredients such as pyraclostrobin and further cross-linking and curing, drug-loaded nano / microcapsules with a particle size of 200-300 nm are obtained. And after process optimization, nano / microcapsules with a drug loading rate of 58-61%, capable of forming a "hat-hook" topological structure with the leaf papillae of crops, controllable release, and adjustable flexibility can be obtained. Description of the Drawings

[0055] Figure 1 Infrared spectra of lignin and modified lignin prepared in Example 1.

[0056] Figure 2 Particle size distribution diagram of lignin pesticide microcapsules prepared in Example 2.

[0057] Figure 3 SEM image of lignin pesticide microcapsules prepared in Example 2.

[0058] Figure 4 Release curves of PYR@MC prepared in Example 2 at different temperatures.

[0059] Figure 5 Release curves of PYR@MC prepared in Example 2 under different pH conditions.

[0060] Figure 6 Release curves of PYR@MC prepared in Example 2 at different laccase concentrations.

[0061] Figure 7Photodegradation resistance performance curves of PYR@MC and PYR prepared in Example 2. Detailed implementation manners

[0062] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0063] The transmission electron microscope used in the examples is HT-7700 field emission transmission electron microscope (Hitachi, Japan); the thermal field emission scanning electron microscope (Zeiss G300); the liquid chromatography is Shimadzu LC-10AT; the particle size analyzer is Nano-ZS90 laser particle size analyzer.

[0064] Example 1

[0065] (1) Preparation of modified lignin

[0066] Under nitrogen protection, 2 grams of alkali lignin was dissolved in 60 milliliters of 10% LiCl / DMF by mass concentration and dissolved at 90 °C. After complete dissolution, the temperature was lowered to 30 °C, and 2 grams (20 millimoles) of triethylamine was added dropwise within 15 minutes and reacted for 15 minutes. 2 grams (20 millimoles) of methacryloyl chloride was added dropwise within 15 minutes and reacted at 50 °C overnight (12 h). It was cooled to room temperature, poured into water for precipitation, centrifuged and separated, and the solid was dried in vacuum (-0.1 Mpa vacuum degree, dried at 30 °C to constant weight); the modified lignin was obtained.

[0067] (2) Preparation of lignin nanoparticles

[0068] 150 milligrams of the modified lignin obtained in step (1) was completely dissolved in 1.5 milliliters of acetone. An aqueous solution of 10 milliliters of 0.2% sodium dodecyl sulfate by mass concentration was prepared and weighed. The lignin acetone solution was added dropwise to the aqueous solution and stirred rapidly. It was stirred rapidly at 50 °C for 1-2 hours. After the acetone was completely volatilized, a lignin nanoparticle suspension with a mass concentration of 1.5% (the system mass was the weighed mass) was obtained.

[0069] (3) Preparation of lignin Pickering emulsion

[0070] The lignin nanoparticle suspension prepared in the above step (2) was used as the aqueous phase; 1000 milligrams of pyraclostrobin, 150 milligrams of cross-linking agent (TMPMP) were dissolved in 500 milligrams of methyl myristate, and 25 milligrams of AIBN was dissolved in 500 milligrams of cyclohexanone. The mixture was used as the oil phase. Then the oil phase and the aqueous phase were mixed and sheared at 10000 rpm for 5 minutes using a high-shear emulsifier to obtain an O / W type lignin Pickering emulsion.

[0071] (4) Preparation of lignin microcapsules

[0072] Stir and react the above emulsion at 60 °C for 6 hours to obtain a lignin microcapsule suspension.

[0073] Example 2

[0074] (1) Preparation of modified lignin

[0075] Under nitrogen protection, dissolve 2 g of alkali lignin in 60 mL of 10% LiCl / DMF and dissolve it at 90 °C. After complete dissolution, cool to 30 °C and add 2 g (20 mmol) of triethylamine dropwise and react for 15 minutes. Add 2 g (20 mmol) of methacryloyl chloride dropwise and react overnight at 50 °C. Cool to room temperature, pour into water for precipitation, centrifuge, and dry the solid under vacuum.

[0076] (2) Preparation of lignin nanoparticles

[0077] Completely dissolve 150 mg of modified lignin in 1.5 mL of acetone. Prepare an aqueous solution containing 0.2% sodium dodecyl sulfate in 10 mL. Dropwise add the lignin acetone solution to the aqueous solution and stir rapidly. Stir rapidly at 50 °C for 1 - 2 hours. After complete evaporation of acetone, obtain a lignin nanoparticle suspension with a concentration of 1.5%.

[0078] (3) Preparation of lignin Pickering emulsion

[0079] Use the lignin nanoparticle suspension prepared in step (2) as the aqueous phase; dissolve 350 mg of pyraclostrobin and 150 mg of cross - linker (TMPMP) in 500 mg of methyl myristate, and dissolve 25 mg of AIBN in 500 mg of cyclohexanone as the oil phase. Then mix the oil phase and the aqueous phase, and use a high - shear emulsifier to shear at 10000 rpm for 5 min to obtain an O / W type lignin Pickering emulsion.

[0080] (4) Preparation of lignin microcapsules

[0081] Stir and react the above emulsion at 60 °C for 6 hours to obtain a lignin microcapsule suspension. The drug - loading rate is 20%.

[0082] Measure the particle size distribution of the microcapsules in the lignin microcapsule aqueous suspension prepared in this example using a Malvern Zetasizer Nano ZS90. The results are as Figure 1 shown, and the average particle size is 206.53 nm.

[0083] Example 3

[0084] (1) Preparation of modified lignin

[0085] Under nitrogen protection, 2 g of alkali lignin was dissolved in 60 mL of 10% LiCl / DMF and dissolved at 90 °C. After complete dissolution, the temperature was lowered to 30 °C, and 2 g (20 mmol) of triethylamine was added dropwise and reacted for 15 minutes. 2 g (20 mmol) of methacryloyl chloride was added dropwise and reacted overnight at 50 °C. It was cooled to room temperature, poured into water for precipitation, centrifuged, and the solid was dried in vacuum.

[0086] (2) Preparation of lignin nanoparticles

[0087] 150 mg of the modified lignin was completely dissolved in 1.5 mL of acetone. An aqueous solution containing 0.2% sodium dodecyl sulfate was prepared in 10 mL. The lignin acetone solution was added dropwise to the aqueous solution and stirred rapidly. It was stirred rapidly at 50 °C for 1 - 2 hours, and after the acetone had completely evaporated, a lignin nanoparticle suspension with a concentration of 1.5% was obtained.

[0088] (3) Preparation of lignin Pickering emulsion

[0089] The lignin nanoparticle suspension prepared in step (2) was used as the aqueous phase; 500 mg of pyraclostrobin and 150 mg of crosslinking agent (TMPMP) were dissolved in 600 mg of methyl myristate, and 25 mg of AIBN was dissolved in 400 mg of cyclohexanone as the oil phase. Then the oil phase and the aqueous phase were mixed and sheared at 10000 rpm for 5 min using a high-shear emulsifier to obtain an O / W type lignin Pickering emulsion.

[0090] (4) Preparation of lignin microcapsules

[0091] The above emulsion was stirred and reacted at 60 °C for 6 hours to obtain a lignin microcapsule suspension. The drug loading rate was 29.2%.

[0092] The particle size distribution of the microcapsules in the lignin microcapsule aqueous suspension prepared in this example was measured using a Malvern Zetasizer Nano ZS90, and the average particle size was 279.87 nm.

[0093] Example 4

[0094] (1) Preparation of modified lignin

[0095] Under nitrogen protection, 2 g of alkali lignin was dissolved in 60 mL of 10% LiCl / DMF and dissolved at 90 °C. After complete dissolution, the temperature was lowered to 30 °C, and 2 g (20 mmol) of triethylamine was added dropwise and reacted for 15 minutes. 2 g (20 mmol) of methacryloyl chloride was added dropwise and reacted overnight at 50 °C. It was cooled to room temperature, poured into water for precipitation, centrifuged, and the solid was dried in vacuum.

[0096] (2) Preparation of lignin nanoparticles

[0097] Completely dissolve 150 mg of modified lignin in 1.5 mL of acetone. Prepare 10 mL of an aqueous solution containing 0.2% sodium dodecyl sulfate. Dropwise add the lignin acetone solution into the aqueous solution and stir rapidly. Stir rapidly at 50 °C for 1 - 2 hours. After the acetone has completely evaporated, a lignin nanoparticle suspension with a concentration of 1.5% is obtained.

[0098] (3) Preparation of lignin Pickering emulsion

[0099] Use the lignin nanoparticle suspension prepared in step (2) as the aqueous phase; dissolve 350 mg of pyraclostrobin and 150 mg of crosslinker (TMPMP) in 700 mg of methyl myristate, and dissolve 25 mg of AIBN in 300 mg of cyclohexanone as the oil phase. Then mix the oil phase and the aqueous phase, and shear at 10000 rpm for 5 min using a high-shear emulsifier to obtain an O / W-type lignin Pickering emulsion.

[0100] (4) Preparation of lignin microcapsules

[0101] Stir and react the above emulsion at 60 °C for 6 hours to obtain a lignin microcapsule suspension.

[0102] Use a Malvern Zetasizer Nano ZS90 to measure the particle size distribution of the microcapsules in the lignin microcapsule aqueous suspension prepared in this example. The average particle size is 252.23 nm.

[0103] Example 5

[0104] (1) Preparation of modified lignin

[0105] Under nitrogen protection, dissolve 2 g of alkali lignin in 60 mL of 10% LiCl / DMF and dissolve at 90 °C. After complete dissolution, cool to 30 °C, dropwise add 2 g (20 mmol) of triethylamine, and react for 15 minutes. Dropwise add 2 g (20 mmol) of methacryloyl chloride and react at 50 °C overnight. Cool to room temperature, pour into water for precipitation, centrifuge, and dry the solid under vacuum.

[0106] (2) Preparation of lignin nanoparticles

[0107] Completely dissolve 150 mg of modified lignin in 1.5 mL of acetone. Prepare 10 mL of an aqueous solution containing 0.2% sodium dodecyl sulfate. Dropwise add the lignin acetone solution into the aqueous solution and stir rapidly. Stir rapidly at 50 °C for 1 - 2 hours. After the acetone has completely evaporated, a lignin nanoparticle suspension with a concentration of 1.5% is obtained.

[0108] (3) Preparation of lignin Pickering emulsion

[0109] Use the lignin nanoparticle suspension prepared in step (2) as the aqueous phase; dissolve 350 mg of pyraclostrobin and 150 mg of crosslinker (TMPMP) in 800 mg of methyl myristate, and dissolve 25 mg of AIBN in 200 mg of cyclohexanone as the oil phase. Then mix the oil phase and the aqueous phase, and shear at 10000 rpm for 5 min using a high-shear emulsifier to obtain an O / W type lignin Pickering emulsion.

[0110] (4) Preparation of lignin microcapsules

[0111] Stir and react the above emulsion at 60 °C for 6 hours to obtain a lignin microcapsule suspension.

[0112] Use a Malvern Zetasizer Nano ZS90 to measure the particle size distribution of the microcapsules in the lignin microcapsule aqueous suspension prepared in this example, and the average particle size is 418.73 nm.

[0113] Example 6

[0114] (1) Preparation of modified lignin

[0115] Under nitrogen protection, dissolve 2 g of alkali lignin in 60 mL of 10% LiCl / DMF and dissolve at 90 °C. After complete dissolution, cool to 30 °C, dropwise add 2 g (20 mmol) of triethylamine, and react for 15 minutes. Dropwise add 2 g (20 mmol) of methacryloyl chloride and react at 50 °C overnight. Cool to room temperature, pour into water for precipitation, centrifuge and separate, and dry the solid under vacuum.

[0116] (2) Preparation of lignin nanoparticles

[0117] Completely dissolve 150 mg of modified lignin in 1.5 mL of acetone. Prepare an aqueous solution containing 0.2% sodium dodecyl sulfate in 10 mL. Dropwise add the lignin acetone solution to the aqueous solution and stir rapidly. Stir rapidly at 50 °C for 1 - 2 hours, and after complete evaporation of acetone, obtain a 1.5% lignin nanoparticle suspension.

[0118] (3) Preparation of lignin Pickering emulsion

[0119] Use the lignin nanoparticle suspension prepared in step (2) as the aqueous phase; dissolve 1000 mg of pyraclostrobin and 150 mg of crosslinker (TMPMP) in 900 mg of methyl myristate, and dissolve 25 mg of AIBN in 100 mg of cyclohexanone as the oil phase. Then mix the oil phase and the aqueous phase, and shear at 10000 rpm for 5 min using a high-shear emulsifier to obtain an O / W type lignin Pickering emulsion.

[0120] (4) Preparation of lignin microcapsules

[0121] The above emulsion was stirred and reacted at 60 °C for 6 hours to obtain a lignin microcapsule suspension. The drug loading rate was 58.6%.

[0122] The particle size distribution of the lignin microcapsule aqueous suspension prepared in this example was measured by Malvern Zetasizer Nano ZS90, and the average particle size was 383.13 nm.

[0123] Effect description:

[0124] Taking Example 1 as an example to illustrate the effect.

[0125] In order to verify that the modification of lignin was successful, infrared spectroscopy characterization was performed on the raw material kraft lignin and the modified lignin (Lignin-MA) used in Example 1, as Figure 1 shown. For the raw material kraft lignin, the absorption peaks caused by the stretching vibrations on phenolic hydroxyl and alcoholic hydroxyl are at 3500 cm -1 ; the C-H stretching vibration peaks in methyl and methylene are near 2933 cm -1 . Compared with the raw material kraft lignin, the modified lignin is significantly weakened at 3500 cm -1 ; at the same time, the C=O of the ester and the C=C of the alkene signals are significantly enhanced at 1750 cm -1 and 950 cm -1 . Therefore, the infrared spectrum confirmed the successful modification of lignin.

[0126] Taking Example 2 as an example to illustrate the effect.

[0127] Example 2 has a small particle size, good pesticide dispersion, good absorption and conduction performance, and higher drug efficacy.

[0128] The particle size distribution of the lignin microcapsule aqueous suspension prepared in this example was measured by Malvern Zetasizer Nano ZS90. It can be seen that it is a single-peak distribution. The results are as Figure 2 shown. The average particle size is 206.53 nm, with a low peak at about 100 nm and a high peak at about 500 nm. Figure 3 This is the scanning electron micrograph of the lignin pesticide microcapsule prepared in Example 2. It can be seen that the microcapsules are in an irregular deflated spherical shape and the surface is relatively smooth.

[0129] The application performance of the pesticide-loaded lignin microcapsules was measured. From Figure 4It can be seen that the encapsulated microcapsule PYR@MC has temperature responsiveness. The release rate is moderate in an environment of 25°C, and the cumulative release amount is 44.98% after 48 h. The release rate is slightly higher than that at room temperature in an environment of 35°C. The release rate is the slowest in an environment of 15°C, and the cumulative release amount is only 31.91% after 48 h.

[0130] From Figure 5 It can be seen that the encapsulated microcapsule PYR@MC has pH responsiveness. The release rate is the slowest in an environment with pH = 7, and the cumulative release amount is 61.60% after 48 h. The release rates in environments with pH = 5 and 9 are significantly higher than that in the environment with pH = 7, and the cumulative release amount is about 90% after 48 h.

[0131] From Figure 6 It can be seen that the encapsulated microcapsule PYR@MC has laccase responsiveness. In an environment without laccase, the drug hardly releases, and the cumulative release amount is still lower than 5% after 20 h. The release rates in environments with concentrations of 5 U / g and 10 U / g are significantly higher than that in the environment without laccase, and the cumulative release amounts are 42.02% and 64.30% respectively after 10 h.

[0132] From Figure 7 It can be seen that with the extension of the UV irradiation time, the content of the original drug pyraclostrobin decreases rapidly, and its effective retention rate is only 4.16% after irradiation for 240 min. While the degradation rate of pyraclostrobin in PYR@MC is slower, and its retention rate still remains at a relatively high level of 20.73% after irradiation for 72 h. This is because lignin has good UV absorption performance. Using lignin as the wall material of the microcapsule has a good protective effect on the photosensitive pesticide pyraclostrobin and effectively improves its photostability.

[0133] Figures 4 to 7 The test methods for each item of data are as follows:

[0134] (1) Determination of pyraclostrobin content by HPLC: The analytical column is an Agilent ZORBAX SB-C18 column (4.6×250 mm, 5.0 μm), the mobile phase is V(methanol):V(water)=80:20; the flow rate is 1.0 mL / min; the detector is an ultraviolet detector, the detection wavelength is 254 nm, the injection volume is 20 μL, the column temperature is 40°C, and quantitative analysis is carried out by the standard curve method.

[0135] (2) Figure 4: Accurately measure 0.1 g of the microcapsule suspension into a dialysis bag with a molecular weight cut-off of 1000. Add 2 mL of ethanol / water (45 / 55, v / v) mixed solution to the dialysis bag, and then place the dialysis bag into 100 mL of ethanol / water (45 / 55, v / v) mixed solution. Place the brown glass bottle in a cold trap at 15 °C and a constant temperature shaker at 25 °C, and continuously oscillate or stir in a water bath at 35 °C; take 1 mL of solution from outside the dialysis bag at regular intervals, filter it through a 0.45 μm organic syringe filter head, and then measure the concentration of pyraclostrobin by HPLC. After each sampling, supplement 1 mL of ethanol / water (45 / 55, v / v) mixed solution; use time as the abscissa and the cumulative release percentage of pyraclostrobin as the ordinate to plot the release curve of pyraclostrobin.

[0136] (3) Figure 5 : Accurately measure 0.1 g of the microcapsule suspension into a dialysis bag with a molecular weight cut-off of 1000. Add 2 mL of ethanol / PBS buffer solution (30 / 70, v / v) mixed solution to the dialysis bag, and then place the dialysis bag into 100 mL of ethanol / PBS buffer solution (30 / 70, v / v) mixed solution. Place the brown glass bottle in a constant temperature shaker at 150 rpm and 25 °C and continuously oscillate or stir; take 1 mL of solution from outside the dialysis bag at regular intervals, filter it through a 0.45 μm organic syringe filter head, and then measure the concentration of pyraclostrobin by HPLC. After each sampling, supplement 1 mL of ethanol / PBS buffer solution (30 / 70, v / v) mixed solution; use time as the abscissa and the cumulative release percentage of pyraclostrobin as the ordinate to plot the release curve of pyraclostrobin.

[0137] (4) Figure 6 : Accurately measure 0.1 g of the microcapsule suspension into a dialysis bag with a molecular weight cut-off of 1000. Add 2 mL of 1% Tween 80 aqueous solution to the dialysis bag, and then place the dialysis bag into 100 mL of 1% Tween 80 aqueous solution. Place the brown glass bottle in a constant temperature shaker at 150 rpm and 25 °C and continuously oscillate; take 1 mL of the supernatant at regular intervals, filter it through a 0.45 μm aqueous syringe filter head, and then measure the concentration of pyraclostrobin by HPLC. After each sampling, supplement 1 mL of 1% Tween 80 aqueous solution; use time as the abscissa and the cumulative release percentage of pyraclostrobin as the ordinate to plot the release curve of pyraclostrobin.

[0138] (5) Figure 7 : Weigh a certain mass of the microcapsule suspension and the technical material, and dilute and make up to 50 mL with 1% Tween aqueous solution respectively (the concentration of the active ingredient is 50 μg·mL -1) Pipette 1 mL of the above suspension into a 1.5 mL centrifuge tube and place it in an ultraviolet degradation chamber (25 cm × 25 cm × 25 cm), which is equipped with two ultraviolet lamps with a power of 6 W and an emission wavelength of 254 nm. Take out the centrifuge tube at regular intervals, centrifuge it, and take the supernatant for testing the remaining amount of the drug by high-performance liquid chromatography.

[0139] Comparative Example 1:

[0140] (1) Preparation of modified lignin

[0141] Under nitrogen protection, dissolve 2 g of sodium lignosulfonate in 60 mL of 10% LiCl / DMF and dissolve it at 90 °C. After complete dissolution, cool it to 30 °C, dropwise add 2 g (20 mmol) of triethylamine, and react for 15 minutes. Dropwise add 8 g - 10 g of benzoic anhydride and react overnight at 50 °C. Cool to room temperature, pour it into water for precipitation, centrifuge and separate, and dry the solid in vacuo to obtain a benzoic acid esterified sodium lignosulfonate (BLS) nanocarrier sample.

[0142] (2) Preparation of lignin nanoparticles

[0143] Completely dissolve 150 mg of the modified lignin in 1.5 mL of acetone. Prepare an aqueous solution containing 0.2% sodium dodecyl sulfate in 10 mL. Dropwise add the lignin acetone solution to the aqueous solution and stir rapidly. Stir rapidly at 50 °C for 1 - 2 hours. After the acetone has completely evaporated, a 1.5% lignin nanoparticle suspension is obtained.

[0144] (3) Preparation of lignin Pickering emulsion

[0145] Use the lignin nanoparticle suspension prepared in step (2) as the aqueous phase; dissolve 350 mg of pyraclostrobin and 150 mg of crosslinking agent (TMPMP) in 800 mg of methyl myristate, and dissolve 25 mg of AIBN in 200 mg of cyclohexanone as the oil phase. Then mix the oil phase and the aqueous phase and shear it with a high-shear emulsifier at 10000 rpm for 5 min to obtain an O / W type lignin Pickering emulsion. However, since the modified material does not contain olefin groups and cannot crosslink with the crosslinking agent, the formed emulsion has insufficient stability and quickly separates into layers. Encapsulation cannot be achieved subsequently.

[0146] Comparative Example 2:

[0147] (1) Preparation of modified lignin

[0148] Under nitrogen protection, 2 g of alkali lignin was dissolved in 60 mL of 10% LiCl / DMF and dissolved at 90 °C. After complete dissolution, the temperature was lowered to 30 °C, and 2 g (20 mmol) of triethylamine was added dropwise and reacted for 15 minutes. 2 g (20 mmol) of methacryloyl chloride was added dropwise and reacted overnight at 50 °C. It was cooled to room temperature, poured into water for precipitation, centrifuged, and the solid was dried in vacuo.

[0149] (2) Preparation of lignin nanoparticles

[0150] 150 mg of modified lignin was completely dissolved in 1.5 mL of acetone. An aqueous solution containing 0.2% sodium dodecyl sulfate was prepared with 10 mL. The lignin acetone solution was added dropwise to the aqueous solution with rapid stirring. It was rapidly stirred at 50 °C for 1 - 2 hours, and after complete evaporation of acetone, a lignin nanoparticle suspension with a concentration of 1.5% was obtained.

[0151] (3) Preparation of lignin Pickering emulsion

[0152] The lignin nanoparticle suspension prepared in step (2) was used as the aqueous phase; 350 mg of pyraclostrobin was dissolved in 800 mg of methyl myristate as the oil phase. Then the oil phase and the aqueous phase were mixed and sheared at 10000 rpm for 5 min using a high - shear emulsifier to obtain an O / W - type lignin emulsion. However, since no cross - linker was added, it could not cross - link to form a stable Pickering emulsion, so it could not be further encapsulated.

[0153] Comparative example 3:

[0154] (1) Preparation of lignin nanoparticles

[0155] 150 mg of unmodified alkali lignin was completely dissolved in 1.5 mL of acetone. An aqueous solution containing 0.2% sodium dodecyl sulfate was prepared with 10 mL. The lignin acetone solution was added dropwise to the aqueous solution with rapid stirring. It was rapidly stirred at 50 °C for 1 - 2 hours, and after complete evaporation of acetone, a lignin particle suspension with a concentration of 1.5% was obtained.

[0156] (3) Preparation of lignin Pickering emulsion

[0157] The lignin particle suspension prepared in step (2) was used as the aqueous phase; 350 mg of pyraclostrobin. The cross - linker 1,6 - dibromohexane was dissolved in a mixed solvent of 500 mg of dichloromethane and 500 mg of cyclohexanone as the oil phase. Then the oil phase and the aqueous phase were mixed and sheared at 10000 rpm for 5 min using a high - shear emulsifier to obtain an O / W - type lignin Pickering emulsion.

[0158] (4) Preparation of lignin microcapsules

[0159] The above emulsion was stirred and reacted at 60 °C for 6 hours to obtain a lignin microcapsule suspension.

[0160] The particle size distribution of the microcapsules in the lignin microcapsule aqueous suspension prepared in this example was measured using a Malvern Zetasizer Nano ZS90, and the average particle size was above 1000 nm.

[0161] During the invention process of the present invention, it was found that:

[0162] If the methacrylate-modified lignin (containing olefin groups that can be further crosslinked) nanoparticles in Example 2 are changed to benzoate-modified lignin nanoparticles without olefin crosslinking groups; the rest is the same as Example 2. This case can form an oil-water mixed emulsion, but cannot be further crosslinked and solidified into capsules; therefore, it can be seen that different esterification groups for modification affect the fineness and stability of the subsequent Pickering emulsion, and further affect the feasibility of crosslinking and solidifying into capsules.

[0163] If "the methacrylate-modified lignin nanoparticles in Example 2 are first mixed with the drug-containing oil phase and emulsified into a Pickering emulsion under the action of a crosslinking agent" is changed to: an aqueous suspension of modified lignin nanoparticles is directly mixed with the drug-containing oil phase solution to form an emulsion without adding a crosslinking agent and an initiator; the rest is the same as Example 2. This case can form an oil-water mixed emulsion, but cannot be further crosslinked and solidified into capsules. Therefore, it can be seen that the selection of the crosslinking agent and the initiator is crucial and further affects the feasibility of crosslinking and solidifying into capsules.

[0164] If "the methacrylate-modified lignin nanoparticles in Example 2 are first mixed with the drug-containing oil phase and emulsified into a Pickering emulsion under the action of a crosslinking agent" is changed to: unmodified alkali lignin is dissolved in a dosage form solvent and then dispersed in water to form a nano-suspension, and under the condition of preferably selecting other suitable crosslinking agents, it is mixed with the drug-containing oil phase solution to form a Pickering emulsion; the rest is the same as Example 2. This case can form a Pickering emulsion, but since the alkali lignin is not lipophilically modified, after being dissolved in acetone and then dispersed in water to form a nano-particle suspension, it has strong hydrophilicity. Although other crosslinking agents are selected later and can be crosslinked into capsules, the particle size after encapsulation is relatively large. Therefore, it can be seen that the lipophilic modification of alkali lignin is crucial, directly affecting the fineness and stability of the subsequent Pickering emulsion, and further affecting the particle size of crosslinked capsules.

[0165] The above embodiments are preferred embodiments of the present invention, but 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. Preparation method of lignin-based sustained-release Pickering microcapsules, characterized in that The following steps are included in sequence: (1) Preparation of modified lignin Under nitrogen protection, 2 g of alkali lignin was dissolved in 60 ml of 10% LiCl / DMF at 90°C; after complete dissolution, the temperature was lowered to 30°C, 2 g of triethylamine was added, and the reaction was continued for 15 minutes; 2 g of methacryloyl chloride was added, and the reaction was continued at 50°C overnight; the mixture was cooled to room temperature, poured into water for precipitation, centrifuged, and the solid was dried in vacuum; (2) Preparation of lignin nanoparticles Dissolve 150 mg of modified lignin in 1.5 ml of acetone, and prepare 10 ml of an aqueous solution containing 0.2% sodium dodecyl sulfate; add the lignin acetone solution to the aqueous solution and stir rapidly; stir rapidly at 50° C. for 1-2 hours, and after the acetone is completely evaporated, obtain a lignin nanoparticle suspension with a concentration of 1.5%; (3) Preparation of lignin Pickering emulsion The lignin nanoparticle suspension prepared in step (2) is used as the aqueous phase; 350 mg of pyraclostrobin and 150 mg of a cross-linking agent, TMPMP, are dissolved in 500 mg of methyl tetradecanoate, and 25 mg of AIBN is dissolved in 500 mg of cyclohexanone as the oil phase; the oil phase and the aqueous phase are then mixed, and a high shear emulsifier is used to shear at 10,000 rpm for 5 min to obtain an O / W type lignin Pickering emulsion; (4) Preparation of lignin microcapsules The emulsion was stirred and reacted at 60° C. for 6 hours to obtain a lignin microcapsule suspension.

2. Lignin-based sustained-release Pickering microcapsules prepared by the method of claim 1.

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