Efficient Encapsulation and Controlled Release of the Pesticide Emamectin Benzoate in Polylactic Acid Microspheres Prepared by Modified Solvent Evaporation

Emamectin benzoate (EB) is a highly effective broad-spectrum insecticide and acaricide. However, because EB is easily degraded, the conventional formulations of EB are often overapplied. In this study, polylactic acid (PLA)-based microspheres were prepared using the modified solvent evaporation method for the controlled release of EB. The microspheres were optimized to achieve higher EB loading. The effects of process parameters on the properties of microspheres, including encapsulation efficiency (EE), particle size, and pesticide loading, were investigated. Additionally, the controlled release behavior of EB microspheres was compared with that of conventional EB emulsifiable concentrate (EC). Spherical-shaped microspheres were obtained with an EE reaching 90.63 ± 1.90%, and introducing an external aqueous phase into the system can significantly enhance the EE of microspheres by over 30%. FTIR, DSC, and XRD analyses indicate that the preparation process of PLA microspheres was mainly physical encapsulation and had no chemical effect on EB. Notably, the EB microspheres displayed more potent control efficacy compared to commercial formulation EB EC against Plutella xylostella. The corrected mortality for the EB microspheres reached 90.00 ± 5.77% after 21 days of application, whereas the corrected mortality for the EB EC was only 19.23 ± 6.66% after 14 days of application. Our study demonstrates that EB-encapsulated PLA microspheres have strong potential as environmentally friendly control release EB formulations.