Controlled release of urea encapsulated by starch-g-poly(l-lactide)

This paper presented a new approach for preparing a new type of slow-release membrane-encapsulated urea fertilizer with starch-g-PLLA as biodegradable carrier materials. By solution-casting and washing rapidly with water the urea was individually encapsulated within the starch matrix modified by l-lactide through in situ graft-copolymerization. The release behavior of urea encapsulated in the films was studied, and following conclusions were achieved: (1) the introduction of hydrophobic PLLA reduced the swellability of starch matrix and decreased the release rate of urea; (2) the urea release rate could be controlled from several hours to 1 day by adjusting the graft efficiency; (3) scanning electron microscopy revealed that the urea encapsulated within the starch matrix was uniformly dispersed in the form of tiny cell and the urea encapsulated in the modified starch film released through a diffusion mechanism. Therefore, the modified starch products for controlled release could be expected to have widely potential application in agriculture industry as fertilizer carrier.