Development of a controlled release formulation based on a starch matrix system.

Controlled release formulation (CRF) of the insecticide acetamiprid was made using tapioca starch, urea and sodium borate. The data show the recovery of this CRF process is > 95.43%, there is no obvious difference with increase of sodium borate added, however, with the increase of urea in the mixture, the formulation has a decrease recovery. In stability test, the decomposition rate of acetamiprid CRF was less one tenth than that of the acetamiprid emulsifiable concentrate (EC) under UV radiation. The release kinetics of acetamiprid from granules with variation content of urea, sodium borate and granule sizes were evaluated in water under laboratory condition. The release data were fitted to the generalized model Mt/Mz = kt(n), where Mt/Mz is the percentage of insecticide released at time t, k and n are constants, and n is constant that indicates the mechanism of release. The results indicated that the release of acetamiprid was diffusion-controlled. The time taken for 50% of the active ingredient to be released into water, T50, was also calculated for the comparison of formulations. The results showed that the formulation with the increasing urea in formulation had the higher value of T50, which means a slower release of the active ingredient, while that the formulation with the increasing sodium borate in formulation had the lower value of T50, which means a faster release of the active ingredient. It was also found that as the size of this formulation decreased, the release of the active ingredient was faster.