Robert E. Wing

Amylose content of starch controls the release of encapsulated bioactive agents

Abstract Controlled release of the herbicide butylate [ S -ethyl bis(2-methylpropyl) carbamothioate] from a non-chemically modified starch matrix has been achieved. Steam injection cooking of cornstarch or mixtures of starches with varying amylose content, followed by active agent addition, drying and grinding yields encapsulated products showing controlled slow release of active agent. As the amylose content increases, the rate of release decreases due to the ability of amylose to retrograde (starch chain association). As the amylose content is reduced to about 10% the efficiency of active agent encapsulation nears 100%. Encapsulated products consisting only of starch and an active agent should be useful in a variety of applications, i.e. food, feed or agriculture.

Factors affecting release of butylate from calcium ion-modified starch-borate matrices

Abstract Controlled release of the herbicide butylate [S-ethyl-bis(2-methylpropyl) carbamothioate] from a starch-borate matrix was modified by incorporating calcium chloride during the matrix-forming step. The addition of calcium chloride, known to be a starch-complexing agent, before borate addition caused the release of butylate to be slower than with borate alone. Varying the amounts of calcium chloride added gave a series of products with different butylate release rates. Varying the pH during product preparation also influenced butylate release. Re-evaluation of butylate release after storing the products for several months indicated the starch had undergone additional retrogradation, since butylate release decreased by 10–30% over that measured originally. Drying freshly prepared samples in an oven (130°C for 90 min) vs air drying (25° C for 24 h) causes a moderate slowing of butylate release. The ability to vary herbicide release rates will serve as a basis for producing starch-encapsulated herbicides for particular end uses.

BIOACTIVITY OF CONTROLLED RELEASE FORMULATIONS OF STARCH­ ENCAPSULATED EPTC*

Abstract Using a bioassay technique, the biological activities of starch-encapsulated formulations of EPTC (S-ethyl dipropylthiocarbamate) were determined in relationship to their controlled release characteristics. The bioactivity of the highly volatile herbicide EPTC was retained on a wet soil surface for 6 to 8 days by starch encapsulation utilizing several crosslinking processes (both chemical and non-chemical) and starches with different ratios of amylopectin to amylose. The rate of release, a measure of the integrity of the granule, depended on the nature of the starch and the crosslinking process. With the herbicide EPTC, encapsulation with a pearl or high amylose starch utilizing the jet-cooking process produced the best controlled release formulation even under the most adverse conditions.

Comparison of steam injection cooking versus twin-screw extrusion of pearl cornstarch for encapsulation of chloroacetanilide herbicides

Abstract Liquid chloroacetanilide herbicides were encapsulated more effectively in a 30 mm twin-screw extruder at 35% starch solids than in a steam injection cooking/Sigma blade mixing process. Excellent mixing in the twin-screw extruder allowed the use of a starch level of 65% and provided for more efficient encapsulation. Extruder prepared products had smaller cells of active agent (via SEM), decreased swellability and slower release of active agent into water than steam injection cooked samples. Using liquid metolachlor, swellability of extruded products increased and encapsulation decreased as starch solids were increased from 35% to 65%. After alachlor had been melted at 50°C, injected, and the product extruded, it solidified in the starch matrix and was more effectively encapsulated than metolachlor. Increasing the concentration of active ingredient in the encapsulated product from 10 to 20% decreased swellability, rate of release into water and encapsulation efficiency. When a 57 mm twinscrew extruder was used to scale up the process for continuous production, encapsulation improved if the water content of the extrudates was reduced to below 10% before grinding.