| Low utilization is the fundamental reason for limiting the reduction use and high efficiency of pesticide.In order to meet the principle of environment friendliness and sustainable agricultural development,environmental-friendly pesticide preparation has been strived to develop.Sustained/controlled release pesticide microcapsules can protect pesticides from environmental factors and achieve long-lasting release owning to the special core-shell structure,which are of great practical significance to study as its advantages.In this study,avermectin-loaded urea-formaldehyde resin microcapsules(UF-Avm-MCP)were prepared by in-situ polymerization in two steps.Firstly,oil-phase solvent system and the ratio of formaldehyde to urea(F/U)were selected for this process.Then FTIR,TG,SEM and granulometer were used to characterize the structure,composition,morphology and size distribution of microcapsules prepared by different surfactants,core-shell ratio and acidizing time.The process conditions were determined as follows:Xylene and SDBS compound with 0.3%gelatin were selected as oil-phase solvent and emulsifier respectively.When the molar ratio of F/U was 1.75 and the core-shell ratio was 0.5:1,UF-Avm-MCP with 1?5?m particle size and uniform size distribution were prepared at 3 hours acidizing time.The agglomeration and self-agglomeration are effectively improved,and the encapsulation efficiency is increased to 64.38%.Pesticide microcapsules should have great biocompatibility and biodegradability especially used in biological environment,but urea-formaldehyde resin(UF)has poor degradation ability to achieve the sustained/controlled release.However,the biopolysaccharides as modifier is different.In this study,sodium alginate(SA)was added to the condensation polymerization of UF.The results showed composite shells were prepared successfully,and sphericity,dispersion,thermal stability and encapsulation efficiency of composite microcapsules were improved.The effects of SA,different temperatures and pH on release performance of microcapsules were studied in 30%(v/v)ethanol.Korsmeyer-Pappas model was used to fit the cumulative drug release results,and the correlation coefficient was greater than 0.97.The experiment designed targeting panonychus citri results showed that the composite microcapsules have higher release ability than UF microcapsules as the cumulative release was increased from 31.8%to 47.5%within 98 days.Moreover,the drug release behavior of modified microcapsules exhibit some pH and temperature dependence.More than 50%of the avermectin added was released within 27 days in acidic medium at 25 ?.The drug release behavior was controlled by difffusion,dissolution,osmosis,swelling and other mechanisms.In reality,we can maximize the pest resistance of pesticides and effectively protect the growth of crops according to the pH of soil environment and the spraying time of slow-release pesticides. |
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