Influence of Compositions of Controlled Release Formulationson the Release Rate of Metolachlor

The controlled release formulations (CRFs) of herbicide metolachlor were prepared using alginate /bentonites as composite carriers.The influence of formulation compositions,such as the loading amount of herbicide,the ratio of carrier materials,and the types of bentonites,on the release rate was investigated.Ritger and Peppas equation was used to analyze the release kinetics,and the time taken for 50% of the metolachlor to be released (t50) was calculated to compare with the release rate from various formulations.When the alginate/bentonite composite carriers were used,the t50 values varied between 29.4 h to 68.0 h,depending on the change of loading amount of herbicide and ratio of carrier materials.The composite carriers performed much better than the pure organically modified bentonite (t50=5.9 h).But when the organically modified bentonite was used together with alginate,the t50 increased to 110 h.The n values (0.436~0.496) of release kinetics of metolachlor from the CRFs were close to that of Fickian diffusion model,indicated a diffusion-dominated release mechanism.