ENCAPSULATION OF EPTC IN STARCH BY TWIN-SCREW EXTRUSION

A twin-screw extruder was used for encapsulation of the herbicide EPTC (S-ethyl dipropylcarbamothioate) in starch. Three starch/water ratios, 35/65, 50/50, and 65/35, were evaluated for efficiency to encapsulate 13.9% EPTC on a dry starch basis. Analysis of extrudates, after drying and grinding to the desired particle size, showed recovery of active ingredient (a.i.) and effectiveness of encapsulation to be best at 35% starch solids (35/65 starch/water ratio). Scanning electron micrographs showed smaller and a more even distribution of a.i. at 35% starch. Suspending particles in water caused a release of EPTC which increased with agitation and smaller mesh size. Air-dried particles released EPTC more slowly than over-dried particles of the same mesh range. Particles from extrusion at 35% solids released a.i. more slowly than those from extrusion at 65% solids. The slowest releasing particles showed the least swellibility. EPTC was also encapsulated at 10.2% a.i. using 20% and 35% starch solids with steam-injection cooking followed by Sigma blade mixing for comparison with an extrusion. Herbicide retention and encapsulation were superior, release of a.i. into water was slower, and swelling of particles was less in twin-screw extrusion prepared products.