Cationic Starch Modified Bentonite-Alginate Nanocomposites for Highly Controlled Diffusion Release of Pesticides

To promote the controlled release efficacy of nanocomposites based on alginate and bentonite, (3-chloro-2-hydroxypropyl)trimethyl ammonium grafted starch was prepared and used as modifying agent of the clay. The nanocomposites were characterized by FTIR, XRD, SEM and TG analysis, to reveal the structural effects on the swelling property of the matrix and the release of alachlor, the model compound. Thermodynamics study indicated that the adsorption of alachlor on the bentonite was dominated by hydrophobic interaction with the siloxane surface of the clay and enhanced by the binding of the cationic starch. The electrostatic attraction between alginate and cationic starch bound on the surface also decreased the aggregation of bentonite platelets, leading to a more compact structure of the nanocomposites. The higher adsorption capability and lower permeability of the matrix resulted in a slower release of alachlor, which was dominated by Fickian diffusion mechanism. The release of alachlor first decreased and then increased with increasing content of bentonite and cationic starch modified bentonite in the nanocomposites, reaching a minimum around weight percentage 10%, at which the time taken for 50% of active ingredient to be released were 4.4 and 7.3 times that for the release from pure alginate hydrogel.