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 cornstarc
h were preblended dry, processed with water and herbicide in the extru
der at 70-95 degrees C, and extruded at 65% solids using an intense mi
xing screw. The extrudates were dried, milled, sieved (14-20 and 20-40
mesh), and analyzed for level of entrapped herbicide. The effect of v
arious levels of clay and other variables on encapsulation efficiency,
swellability, and release rates of the products in water were determi
ned. The study showed that clay in the preblends of up to 50% had rath
er small effects on encapsulation efficiency and release rates of the
products in water. As little as 20% starch in the blends remarkably sl
owed 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, m
etolachlor, and water. In all cases metolachlor was released more quic
kly than atrazine from the products (10-27% active ingredient).