CONTROLLED-RELEASE OF DIURON FROM GRANULES BASED ON A LIGNIN MATRIX SYSTEM

Matrix formulations of the soil-applied herbicide diuron were made usi ng alkali lignins extracted from sugar-cane bagasse, pine and eucalypt us woods. Initial release studies in water were performed on a range o f granules with variation in the lignin, loading of diuron, the granul e size and temperature of immersion. The granules were found to swell in water, to a varying extent depending on the lignin. A porous struct ure was shown to form inside the granules on penetration of water. Wat er 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 g eneralised 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 (hydro xyl, methoxyl and carbonyl) and the release rates from granules made u sing the various lignins.