CLAY AS A CARRIER IN STARCH ENCAPSULATED HERBICIDES PREPARED BY EXTRUSION PROCESSING

Metolachlor and atrazine herbicides were separately incorporated into matrices containing all starch, all clay, and starch/clay blends by a twin-screw extrusion process. A low-cost clay and unmodified cornstarch were preblended dry, processed with water and herbicide in the extruder at 70-95 degrees C, and extruded at 65% solids using an intense mixing screw. The extrudates were dried, milled, sieved (14-20 and 20-40 mesh), and analyzed for level of entrapped herbicide. The effect of various levels of clay and other variables on encapsulation efficiency, swellability, and release rates of the products in water were determined. The study showed that clay in the preblends of up to 50% had rather small effects on encapsulation efficiency and release rates of the products in water. As little as 20% starch in the blends remarkably slowed the release rates compared to that of clay alone. Processing the clay, herbicide and water without starch in the extruder significantly slowed the release rate compared to an unprocessed mixture of clay, metolachlor, and water. In all cases metolachlor was released more quickly than atrazine from the products (10-27% active ingredient).