Controlled release herbicide formulations based on polymeric microspheres

Abstract

A series of polymeric microsphere formulations were prepared and tested for their ability to control the release of an herbicide, Dicamba (DA; 3,6-dichloro-2-methoxybenzoic acid). Microspheres (MSs) were produced from ethyl cellulose (EtCell), polyarylsulfone (PS), or a combination of the two, in the desired size range of 20–40 μm by solvent evaporation or spray drying. Generally, PS MSs could be loaded with more DA (up to nearly 50 wt%) than could the EtCell MSs (maximum loading obtained was 23 wt%). EtCell MSs released DA at a greater rate than did comparable PS MSs under sonication and soil column irrigation release tests. The release rate of DA from the EtCell MSs could be controlled by using different viscosity grades (i.e., molecular weights) of EtCell: higher viscosity EtCell led to a lower DA release rate. The release rate of DA from MSs was also controlled by using a combination of EtCell with PS. Overall, MSs prepared from EtCell, PS or EtCell/PS show promise as controlled release formulations for herbicides.