Preparation and Physicochemical Characteristics of Polylactide Microspheres of Emamectin Benzoate by Modified Solvent Evaporation/Extraction Method

Emamectin benzoate is highly effective against insect pests and widely used in the world. However, its biological activity is limited because of high resistance of target insects and rapid degradation speed in fields. Preparation and physicochemical characterization of degradable microcapsules of emamectin benzoate were studied by modified solvent evaporation/extraction method using polylactide (PLA) as wall material. The influence of different compositions of the solvent in internal organic phase and external aqueous phase on diameter, span, pesticide loading, and entrapment rate of the microspheres was investigated. The results indicated that the process of solvent extraction and the formation of the microcapsules would be accelerated by adding water-miscible organic solvents such as ethyl ether, acetone, ethyl acetate, or n-butanol into internal organic phase and external aqueous phase. Accelerated formation of the microcapsules would result in entrapment rates of emamectin benzoate increased to as high as 97%. In addition, by adding ethanol into the external aqueous phase, diameters would reduce to 6.28 mu m, whereas the loading efficiency of emamectin benzoate did not increase. The PLA microspheres prepared under optimum conditions were smoother and more spherical. The degradation rate in PLA microspheres of emamectin benzoate on the 10th day was 4.29 +/- 0.74%, whereas the degradation rates of emamectin benzoate in methanol solution and solid technical material were 46.3 +/- 2.11 and 22.7 +/- 1.51%, respectively. The PLA skeleton had combined with emamectin benzoate in an amorphous or molecular state by using differential scanning calorimetry (DSC) determination. The results indicated that PLA microspheres of emamectin benzoate with high entrapment rate, loading efficiency, and physicochemical characteristics could be obtained by adding water-miscible organic solvents into the internal organic phase and external aqueous phase.