Preparation, Characterization and Release Properties of beta-Cypermethrin Microcapsules

The solvent evaporation method was adopted to prepare beta-cypermethrin microcapsules, using beta-cypermethrin as core material, ethylcellulose as wall materials. The physical and chemical properties of microcapsules were characterized. The effects of process conditions on appearance, mean particle size and distribution, encapsulation efficiency, loading content and controlled release were studied by single factor experiments. The results indicated that emulsifier types and shearing duration time had significant influence on appearance of microcapsules. The particle size and size distribution decreased with the increasing of emulsifier concentration. When the dosage of Tween. 80 increased from 4% to 8%, the average particle size of microcapsules decreased from 59.9 mu m to 29.8 mu m, and the span reduced from 1. 21 to 0. 72. As the core. wall ratio decreased, there was a gradual increase in both particle size and encapsulation efficiency, but a de. crease in loading content. When the core. wall ratio was 1 : 1. 75, the encapsulation efficiency was more than 70%. The most fitted drug release kinetics model was the Ritger-Peppas model(lgQ = lgk+nlgt). For microcap. sules with similar mean particle sizes and different loading content, the sample with minimum loading content tended to have a lower release rate and cumulative release rate. For microcapsules with similar loading content and diffe-rent mean particle sizes, the sample with largest size tended to have a lower release rate and cumulative release rate.