Study on Sustained-Release Pesticides Blended with Fosthiazate-Stearic Acid/Expanded Perlite

Abstract

The low utilization rate of pesticides makes the migration of pesticides in water and soil, which brings great harm to the ecosystem. The development of pesticide carriers with good drug loading capacity and release control ability is an effective method to realize effective utilization of pesticides and reduce pesticide losses. In this work, fosthiazate-stearic acid/expanded perlite sustained-release particles were successfully prepared by vacuum impregnation using expanded perlite (EP) as carrier, fosthiazate (FOS) as model pesticide and stearic acid (SA) as hydrophobic matrix. The structure and morphology of the samples were studied by BET, FT-IR, TGA, XRD, DSC and SEM. The effects of different mass ratios of FOS to SA on loading capacity and release rate at 24 h were investigated. The sustained release behavior of FOS-SA/EP at different temperatures and pH values was investigated by static dialysis bag method. The results showed that FOS and SA were adsorbed in EP pores by physical interaction. With the mass ratios of FOS to SA decreasing from 7:3 to 3:7, the 24 h release rate of FOS-SA/EP decreased from 18.77% to 8.05%, and the drug loading decreased from 461.32 to 130.99 mg/g. FOS-SA/EP showed obvious temperature response at 25°C, 30°C and 35°C, the cumulative release rate (CRR) of 200 h were 33.38%, 41.50% and 51.17%, respectively. When pH = 5, the CRR of FOS was higher than that of pH = 7, and the CRR of FOS for 200 h were 49.01% and 30.12%, respectively. At different temperatures and pH = 5, the release mechanism of FOS-SA/EP belongs to the Fickian diffusion mechanism; When pH = 7, the diffusion mechanism is dominant, and the dissolution mechanism is complementary.