Evaluation of the Thermosensitive Release Properties of Microspheres Containing an Agrochemical Compound

The purpose of this study was to develop a deeper understanding of the key physicochemical parameters involved in the release profiles of microsphere-encapsulated agrochemicals at different temperatures. Microspheres consisting of different polyurethanes (PUs) were prepared using our previously reported solventless microencapsulation technique. Notably, these microspheres exhibited considerable differences in their thermodynamic characteristics, including their glass transition temperature (T_g), extrapolated onset temperature (T_o) and extrapolated end temperature (T_e). At test temperatures below the T_o of the PU, only 5-10% of the agrochemical was rapidly released from the microspheres within 1 d, and none was released thereafter. However, at test temperatures above the T_o of the PU, the rate of agrochemical release gradually increased with increasing temperatures, and the rate of release from the microspheres was dependent on the composition of the PU. Taken together, these results show that the release profiles of the microspheres were dependent on their thermodynamic characteristics and changes in their PU composition.