Study On The Preparation And Performances Of Avermectin,Emamectin Benzoate Microcapsules

The solvent evaporation method for preparation of pesticide microcapsules has prominent features including simple operation,short cycle,and excellent performance,which overcomes the shortages of other existing methods to prepare pesticide microcapsules.Avermectin and emamectin benzoate are important insecticides varieties in current agriculture and forestry,they have advantages of high efficiency,low toxicity,safety and so on,which are remarkable to prevent pest mites and root-knot nematodes.However,they are easily affected by microorganism and ultraviolet light because of their unstable physicochemical properties.Increasing the amount and times of spraying will lead to the increase of the resistance to pesticide.In this study,avermectin and emamectin benzoate microcapsules were prepared by orthogonal design based on the variables including the dosage of wall materials,the dosage of emulsifier,solvent dosage and other factors,as well as the indexes such as particle size and entrapment efficiency.And the microcapsules performances were characterized by the determination of particle size,FTIR,entrapment efficiency,drug loading,and appearance characteristics observation.Finally,the release characteristics of the microcapsules were characterized by release curve measurement and model fitting in water,acetonitrile,acetonitrile-water and soil.The results of orthogonal design experiment for avermectin microcapsules showed that the dosage of methylene chloride and the dosage of ethylcellulose had extremely significant effect on the particle size.The time of emulsifying had extremely significant effect on the encapsulation efficiency.The surface and internal morphology of the microcapsules showed that the microcapsule(sample 8)had homogeneous particles size,smooth surface;the microcapsule(sample 9)had small and uniform particles size,rough surface.Infrared spectroscopy proved that the avermectin had been entrapped in microcapsules.The optimum formulation(sample 8):30wt%dichloromethane,1wt%ethylcellulose,2wt%emulsifier R3,emulsifying time of 12 min,the D50 of this microcapsule was 80.51 ?m and the encapsulation efficiency was 93.2%.The results of orthogonal design experiment for emamectin benzoate microcapsules showed:the dosage of ethylcellulose had significant effect on the particle size.The dosage of emulsifier had significant effect on the encapsulation efficiency.The surface and internal morphology of the microcapsules showed that the microcapsule(sample 6)had small particles size,larger quantity,smooth surface with a small quantity of holes;the microcapsule(sample 8)had large particles size,rough surface with a large number of holes.Infrared spectroscopy proved that the emamectin benzoate had been entrapped in microcapsules.The optimum formulation(sample 6):30wt%dichloromethane,lwt%ethylcellulose,2wt%emulsifier R4,emulsifying time of 10 min,the D50 of this microcapsule was 56.07 ?m and the encapsulation efficiency was 96.37%.The results of release test of avermectin microcapsules in different media were showed as follows:Release in water:The release of avermectin of sample 8 conformed to the Zero-Order release model.That of sample 9 conformed to the Makoid-Banakar release model and belonged to diffusion release(n<0.45).Release in acetonitrile:The release of avermectin of sample 8 and sample 9 both conformed to the Makoid-Banakar release model and belonged to diffusion release(n<0.45).Release in acetonitrile-water solution:Avermectin technical had completely released in a short period of time(50 h),while the avermectin of sample 8 and 9 still released at a steady rate after 72 h.The release of avermectin of ample 8 and sample 9 both conformed to the Makoid-Banakar release model and belonged to diffusion release(n<0.45).Release in soil:During the first 3 days,the avermectin of sample 9 released abruptly,while the release rate of avermectin of sample 8 gradually increased.The avermectin of sample 9 released slowly at 5-35 days,while that of sample 8 released faster.The results of release test of emamectin benzoate microcapsules in different media were showed as follows:Release in water:The release of emamectin benzoate of sample 6 conformed to the Higuchi release model.That of sample 8 conformed to the Makoid-Banakar release model and belonged to diffusion and dissolution release(0.45<n<0.89).Release in acetonitrile:The release of emamectin benzoate of sample 6 and sample 8 both conformed to the Makoid-Banakar release model.Sample 6 belonged to dissolution release(n<0.89)and sample 8 belonged to diffusion release(n<0.45).Release in acetonitrile-water solution:Emamectin benzoate technical had completely released in a short period of time(7 h),while the emamectin benzoate of sample 6 and 8 still released at a steady rate after 72 h.The release of emamectin benzoate of sample 6 and sample 8 both conformed to the Makoid-Banakar release model and belonged to diffusion release(n<0.45).Release in soil:the emamectin benzoate of sample 6 and sample 8 released at a constant rate over 35 days,but the release rate of emamectin benzoate of sample 6 was greater than that of sample 8.