Correlation Between Gel Strength of Starch-Based Hydrogel and Slow Release Behavior of Its Embedded Urea

Starch-based hydrogels have attracted increasingly attention for application in controlled release fertilizers. However, there is currently a lack of knowledge on ways to characterize this system. In this work, we employed a hot-compression vulcanizer to in-situ synthesize monolithic urea-embedded grafted starch hydrogels with a slab geometry, which facilitates the subsequent measurement of gel strength and urea release kinetics. The results revealed that the greater the gel strength induced by a decreased urea load, an increased graft content, and an increased cross-linking density of starch-based hydrogels, the less the initial burst release of embedded urea. The unavoidable burst release could be ascribed to the heterogeneous network structure of starch-based hydrogels. The network of the hydrogels also afforded an zero-order, or at least time-independent, release kinetics of urea at intermediate stable stage, regardless of their microstructural parameters. Our results could provide a guideline to the design of hydrogel-based fertilizer delivery systems.