Controlled Release of Herbicides Supported on Polysaccharide Based Hydrogels

Abstract

Polymeric hydrogels based on polysaccharides, hydroxyethylcellu lose and dextran, were attained by cross-linking with epichlorohydrin. The cross-linked polymer beads were loaded with 2,4-dichlorophenoxyacetic acid by direct esterification in the presence of carbonyldiimidazole. Loads ranging be tween 0.5 and 2.2 mol of 2,4-dichlorophenoxyacetyloyl groups per glucose unit were obtained. The release of 2,4-D herbicide was investigated in buffered aqueous solution at different pH values (4, 7 and 9) and evaluated with respect to different structural parameters, such as nature of the polymer matrices, cross-linking extent and herbicide loading. A fairly slow release, ranging from 10 to 25% after four months, was recorded under neutral and acid conditions, whereas at pH 9 an initial burst in the release profile, reaching almost 90% release of 2,4-D loading, was observed. In the majority of the cases, the release kinetics are reproduced by the combination of two exponential decay processes, that differ by about three orders of magnitude in their absolute rates.