Preparation, characterization and performance analysis of fosthiazate/expanded perlite sustained-release pesticides

The development of a pesticide-loading system that combines high drug loading and good sustained-release performance is an effective way to reduce pesticide losses and improve utilization of pesticides. In this study, modified waste soybean oil (MSO) and polymethylene polyphenyl polyisocyanate (PM200) were used as raw materials to prepare PM200-MSO. Then, coated fosthiazate/expanded perlite sustained-release pesticides (cFOS/EP) were prepared by disc granulation principle with expanded perlite (EP) as carrier, fosthiazate (FOS) as model pesticide and PM200-MSO as coating material. The results showed that, in PM200-MSO, the –OH of MSO reacted with the –NCO group of PM200 to form carbamate. The surface contact angle of PM200-MSO decreased as the amount of MSO increased. When the amount of PM200 was not less than 50%, FOS leakage from EP was prevented. The pesticide loading (PL) of four pesticides (FOS/EP, cFOS/EP-0, cFOS/EP-1, cFOS/EP-3) was greater than 365.00 mg/g, and kinetic studies showed that FOS release from four pesticides was controlled by diffusion. cFOS/EP-1 had the best sustained-release performance, and its stability at pH5 was better than that at pH7, and the FOS release rate was pH5>pH7, the cumulative release rate (Ri) at 200 h were 58.22% and 46.99%, respectively. The FOS release from cFOS/EP-1 belonged to Fickian diffusion at pH5. When pH = 7, it belonged to non-Fickian diffusion, which was dominated by diffusion and complementary by dissolution. SEM observation confirmed the presence of large protrusions and depressions on the surface of cFOS/EP-1, internal cracks, and slight dissolution of its film structure at pH7.