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To provide effective delay in release, organobentonites with different loading levels of dodecyltrimethylammonium chloride (DTMA) and hexadecyltrimethylammonium chloride (HTMA) were used as modifying agents in the alginate-based controlled release formulation (CRF) containing imidacloprid. The structure of organobentonites was characterized by FTIR and XRD, and adsorption toward imidacloprid was investigated. The results were utilized to reveal the effects of organobentonites on the release of imidacloprid as well as its mechanism, and to evaluate the potential use of organobentonites to modulate the release of imidacloprid. The results showed that organobentonites could reduce the release of imidacloprid from alginate-based granules, different from the natural bentonite that accelerated the release of imidacloprid. The time taken for 50% of the active ingredient to be released, T50, for CRF incorporating organobentonites with DTMA at loading level of 50, 75, 100 and 125% of the clay's cation exchange capacity was 2.12, 1.59, 1.55 and 1.38 times of the value for the formulation without modifying agent, respectively. The values for those incorporating organobentonites with HTMA at the same loading level were 2.61, 2.20, 1.89 and 1.88 times. It was suggested that imidacloprid released via an anomalous transport kinetics predominated by Fickian diffusion and was influenced by the addition of bentonite and organobentonites due to the change of matrix permeability and the interaction with organobentonites. The enhancement of matrix permeability and imidacloprid release resulting from the addition of natural bentonite might be attributed to the lamellar structure and swellability of bentonite in water. In contrast, the matrix permeability and imidacloprid release decreased when organobentonites were used as modifier agents, as a consequence of the hydrophobicity of organobentonite. The results also suggested the feasibility of regulating imidacloprid release via controlling the structure of the organobentonites. An increase in loading level of quaternary ammonium ions could result in an enhancement of the release, while the extension of the alkyl chain slowed down the release of imidacloprid. |
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