Controlled release of diuron from granules based on a lignin matrix system

Matrix formulations of the soil-applied herbicide diuron were made using alkali lignins extracted from sugar-cane bagasse, pine and eucalyptus woods. Initial release studies in water were performed on a range of granules with variation in the lignin, loading of diuron, the granule size and temperature of immersion. The granules were found to swell in water, to a varying extent depending on the lignin. A porous structure was shown to form inside the granules on penetration of water. Water uptake of the granules reached equilibrium after approximately one week for the pine and eucalyptus lignin matrices and after three weeks for the bagasse lignin granules. The release data was fitted to the generalised model M(t)/M(z) = kt(n) + c. The results indicated that the release of diuron was diffusion-controlled The time taken for 50% of the diuron to be released into water, T-50 was also calculated for the comparison of formulations. This value was then used to investigate a possible correlation with key functional groups in the lignins (hydroxyl, methoxyl and carbonyl) and the release rates from granules made using the various lignins.