Structural effects of organobentonites on controlled release of pretilachlor

• Pretilachlor release was sustained by incorporating into organobentonites.
• The release decreased with increasing adsorption capability of organobentonites.
• The release was dominated by diffusion related to the structure of matrix.
• Higher surfactant packing density of organobentonite resulted in slower release.

To provide controlled release properties to the formulation containing pretilachlor, organobentonites with different loading levels of dodecyltrimethyl ammonium chloride (DTMA) and hexadecyltrimethyl ammonium chloride (HTMA) were prepared and used as carrier. The organobentonites were characterized by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analysis, and the adsorption towards pretilachlor was investigated, to reveal the structural effects of organobentonites on the release of pretilachlor. Organobentonites with quaternary alkylammonium surfactant showed excellent adsorption capacity for pretilachlor and greatly reduced its release in water. On the basis of the parameter of an empirical equation used to fit the release data, the release of pretilachlor from organobentonites could be deduced to be predominated by Fickian diffusion mechanism. The time taken for 50% of active ingredient to be released, T50, from DTMA-bentonite with surfactant loading of 60, 80, 100 and 120% of the cation exchange capacity was 12.9, 12.7, 18.5 and 26.7 times of that for the formulation without organobentonites and exhibited good linear relationship with the adsorption constant Kf from the Freundlich equation. Similar results were obtained for HTMA-bentonite. Hydrophobic interaction played a key roll in the adsorption and sustained release of pretilachlor. An increasing loading level of quaternary alkylammonium surfactant on organobentonites generally led to an enhancement of the sustained release. The permeability of organobentonite also had an important impact on the diffusion of the herbicide. The extension of the alkyl chain of the quaternary ammonium surfactant resulted in an increased permeability of organobentonites and release of pretilachlor, owing to the increased basal spacing and lower surfactant packing density.

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