Preparation Of Isocyanate-based Microcapsules And Research On Their Release Regulation

Prochloraz is a broad-spectrum fungicide,which has obvious control effect on fungal diseases of various crops.However,the photo-instability of prochloraz leads to the problems of short effective duration and low utilization rate of pesticides.Pyridaben is an effective and contact-killing acaricide,which can be used to control a variety of phytophagous mites.However,the photo-instability of pyridaben and high toxicity to aquatic organisms seriously hindered the application of pyridaben in the prevention and control of aquatic plant diseases.Microencapsulation of prochloraz and pyridaben can effectively solve the stability of prochloraz and the application of pyridaben in the control of aquatic plant diseases.Therefore,in this paper,the sustained-release microcapsules of prochloraz and self-bursting microcapsules of pyridaben were prepared by interfacial polymerization and characterized.The release mechanism and UV shielding performance of prochloraz microcapsules were evaluated,and the effects of surfactants on the wetting and deposition behavior of the liquid on the surface of wheat leaves were investigated.The morphology and functional groups of pyridaben microcapsules were characterized,and the microcapsules were self-bursting.Meanwhile,release mechanism,stability,UV shielding performance,and deposition effect of microcapsules on citrus leaves were evaluated.The work of this paper is summarized as follows:1.Preparation of prochloraz microcapsules and study on the wetting and deposition behavior of the target surface.(1)Microcapsules of prochloraz were prepared by interfacial polymerization.The optimum conditions were as follows: HMDI was the monomer in oil phase,DETA was the monomer in water phase,and EL-80 was the emulsifier.(2)The prochloraz microcapsules were characterized by optical microscopy,scanning electron microscopy,laser particle size analyzer,and fourier transform infrared spectrometer.The results showed that prochloraz was successfully encapsulated in the polyurea shell,and the encapsulation efficiency was 82.70 %.The microcapsules were spherical,with a smooth and dense surface,and a hollow structure.The particle size distribution of the microcapsules was uniform and conformed to a normal distribution.(3)The release behavior of prochloraz microcapsules in anhydrous methanol/water(40/60)was investigated.When the microcapsules were released for132 h,the cumulative release rate was only 62 %,which had a good sustained-release effect.(4)The prochloraz and microcapsules were irradiated with a mercury lamp to explore the UV shielding performance of prochloraz microcapsules.When irradiated for 4 h,the photolysis rate of microcapsules was 61%,which was much lower than that of prochloraz(97 %).The microcapsules had good UV shielding performance.(5)The effects of surfactants on the wetting and deposition behavior of the liquid on the surface of wheat leaves were investigated.The addition of surfactants could significantly reduce the surface tension and contact angle of the liquid,increase the contact area and adhesion of the liquid on the wheat leaves,and improve the utilization rate of pesticide.2.Preparation and characterization of self-bursting pyridaben microcapsules(1)The water phase monomer and capsule wall material content were screened,and the self-bursting pyridaben microcapsules were prepared by the interfacial polymerization method.(2)The microcapsules of pyridaben were characterized by optical microscope,fourier transform infrared spectrometer,and laser particle size analyzer.The results showed that pyridaben was encapsulated in the polyurethane shell by the reaction of the isocyanate group and the hydroxyl group of polyethylene glycol.The encapsulation efficiency was 95.27 %.The microcapsules are spherical in the water.After the water evaporates,the microcapsules rupture and the contents flow out.They are self-bursting microcapsules.The particle size of microcapsules was approximately normal distribution,and the particle size was almost unchanged after cold and hot storage,and the stability was good.(3)The release behavior of pyridaben microcapsules was studied.When the microcapsule was released for 120 h,the cumulative release rate was 5.3%,indicating that pyridaben microcapsules were almost not released in water.(4)The UV shielding performance of microcapsules was explored.When the UV lamp was irradiated for 2 h,the photolysis rate of pyridaben reached 62.76 %,and the photolysis rate of pyridaben in microcapsules was only 14.89 %.The microcapsules showed excellent UV shielding performance.(5)The deposition effect of microcapsules on citrus leaves was studied.The microcapsules were diluted 500 times and sprayed evenly on the citrus leaves.It was found that most of microcapsules were deposited on the surface of leaves,and the distribution was relatively uniform without obvious aggregation.