POLYMERIC MICROSPHERES FOR CONTROLLED-RELEASE HERBICIDE FORMULATIONS

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), over an extended period of time. Microspheres (MSs) were produced from both ethyl cellulose (EC) and polyarylsulfone (PS) in the desired size range (20-40 mum) by solvent evaporation or spray drying. Generally, PS MSs could be loaded with more DA (up to nearly 50 wt%) than could the EC MSs (maximum loading obtained was 23 wt%). EC MSs released DA at a greater rate than did comparable PS MSs under sonication and in soil column irrigation tests. The release rate of DA from the EC MSs could be controlled by using different viscosity grades (i.e., molecular weights) of EC: higher viscosity EC led to a lower DA release rate. The release rate of DA was also controlled by using a combination of EC with PS. Overall, MSs prepared from EC, PS, or EC/PS show promise as controlled release formulations for herbicides.