Preparation Of Lambda-Cyhalothrin Microcapsules By Two Wall Materials And Their Properties

Lambda-cyhalothrin has many advantages,such as high efficiency,low toxicity,wide insecticidal spectrum and so on.It is an important agricultural insecticide and widely used in pest control.The traditional processing formulations for Lambda-cyhalothrin use a large amount of organic solvent,have poor stability,strong irritation to the skin and eye,it is easily degraded quickly by the environmental impact,and the persistent insecticidal efficacy is short.It has made up for the deficiency of traditional processing formulations by the microencapsulation of Lambda-cyhalothrin.The preparation of pesticide microcapsules by solvent evaporation has the advantages of simple process,short cycle and cost saving,and overcomes the shortcomings of most microcapsule preparation methods.Wall material is an important factor affecting the physicochemical properties of pesticide microcapsules.In this study,ethyl cellulose and polylactic acid were selected as wall materials.The Lambda-cyhalothrin microcapsules were prepared by solvent evaporation.The comprehensive score of microcapsules was used as the inspection index.The preparation technology of two kinds of Lambda-cyhalothrin microcapsules was optimized by response surface method.The physicochemical properties of the microcapsules prepared by the optimum process were characterized,and micromorphology observation,size and distribution of particle size,infrared spectrum,encapsulation efficiency and drug loading were measured,and the release kinetics of two microcapsules in acetonitrile and water medium were compared.The control effect to target organisms of two kinds of Lambda-cyhalothrin microcapsules under different concentrations was studied with the control of German cockroach.The optimum technology of Lambda-cyhalothrin ethyl fiber microcapsule obtained by the response surface method was 12.99 g of solvent,0.51 g of wall material and 2.035 g of emulsifier.The comprehensive score of Lambda-cyhalothrin microcapsules prepared by this process was 0.6191,and the order of influence on the synthetic score of ethyl cellulose microcapsule was:solvent dosage>wall material dosage>emulsifier dosage.The micromorphology observation showed that the particle size was uniform,the distribution was dense,the surface with some small hole was smooth.The infrared spectroscopy showed that the Lambda-cyhalothrin was successfully embedded in the ethyl cellulose.The D50 of the best microcapsule was 38.12 μm,the encapsulation efficiency was 67.4%,and the drug loading was 37.6%.The optimum process for the preparation of Lambda-cyhalothrin polylactic acid microcapsule by response surface method is as follows:the solvent dosage is 6.67 g,the core wall ratio is 1.12:1,and the polyvinyl alcohol dosage is 0.365 g.The comprehensive score of Lambda-cyhalothrin microcapsules prepared by this process is 0.1409.The order of influence on the synthetic score of polylactic acid microcapsules is:solvent dosage>polyvinyl alcohol dosage>core wall ratio.The micromorphology observation showed that the particle size was uniform and smaller,the surface was smooth and round,and the body was semitransparent.The D50 of the best microcapsule was 2.44 μm,the encapsulation efficiency was 92%,and the drug loading was 48%.The results of property research showed that:For the release in acetonitrile:the release rate of Lambda-cyhalothrin in polylactic acid microcapsules was larger than that of ethyl cellulose microcapsule.The release kinetics of ethyl cellulose microcapsules conformed to the Makoid-Banakar release model,and n<0.45,which belongs to diffusion release,and the polylactic acid microcapsules have low fitting degree to the four release models.For the release in water:The release of Lambda-cyhalothrin from two kinds of microcapsules is not obvious.Efficacy test:For three application concentrations,the reduction degree of the lethal effect of polylactic acid microcapsules was less than that of ethyl cellulose microcapsules and emulsion oil in water,and polylactic acid microcapsules had the longest effective period,followed by ethyl cellulose microcapsules.What’s more,the effective period of emulsion was the shortest,but the reduction degree of the lethal effect was the fastest.