Controlled release of phoxim from organobentonite based formulation

Abstract

Organobentonite, prepared by employing dodecyl trimethyl ammonium chloride (DTMAC) and hexadecyl trimethyl ammonium chloride (HTMAC) as modifying agents, was used as carrier of phoxim to obtain controlled release granule. The structure of organobentonite was investigated by XRD, and utilized to reveal the effects on the sorption and release of phoxim. The results indicated that organobentonite was an excellent sorbent towards phoxim and greatly reduced the release of phoxim. It was found that the sorbed quaternary ammonium aggregates together to form organic phase in bentonite interlayer to accommodate the pesticide molecules. The average loading percentages for organobentonite modified with DTMAC and HTMAC at the loading level of 50, 100 and 150% of the clay's cation exchange capacity were 70.8, 75.3, 71.0% and 91.8, 93.9, 90.3%, and the time taken for 50% of phoxim to be release, T50, for the CRF based on the organobentonites was 3.7, 11.8, 10.7 times and 3.4, 10.4, 8.2 times of the value for the formulation without organobentonite, respectively. An enhancement of the release of phoxim could be achieved by increasing the carbon chain of quaternary ammonium. The results also showed that an increase of quaternary ammonium loading via electrostatic interaction significantly slowed down the release of phoxim, whereas that via hydrophobic interaction showed little effect. The results suggested the feasibility of regulating the release of phoxim via controlling the structure of organobentonite.