Controlled Release of Phenylurea Herbicides from a Lignin Matrix:  Release Kinetics and Modification with Urea

The release kinetics of five phenylurea herbicides from granules based on a lignin matrix system were evaluated in water using a static immersion test. The T 50 values, the time taken for 50% of the active ingredient to be released, were used to investigate a possible correlation of the release with the water solubility, octanol−water partition coefficient ( K OW ), and the solubility parameter of the herbicide. A linear correlation of the T 50 value and the K OW of the herbicides was observed. Urea was added to a diuron−lignin matrix as a processing aid and a release modifier. This resulted in an increased rate of release of diuron, and an unexpected chemical reaction between diuron and urea resulted in the formation of dichlorophenylurea (DCPU). As the amount of DCPU formed was very small and it is a metabolite of diuron, its formation is expected to have minimal impact.