Polyacrylamide and methylcellulose hydrogel as delivery vehicle for the controlled release of paraquat pesticide

PAAm–MC hydrogels as a potential delivery vehicle for the controlled release of paraquat pesticide was investigated, as they play an essential role to use hydrogels in controlled release technology. The release kinetics of paraquat was determined using UV–Vis measurements. The release mechanism of paraquat from PAAm–MC hydrogels was investigated through a semi-empirical model proposed by Ritger and Peppas. In general, the initial rate of paraquat release was fast, decreasing after several days, hence indicating that paraquat on the surface (or close to) of hydrogels diffused rapidly after the initial swelling of the gel. Later, the cumulative release occurred in a very controlled and sustained manner, with the paraquat concentration maintaining constant from 15 to 46 days. The paraquat release capacity was dependent on the swelling of the matrix and the density of the network chains. The curves obtained from Peppas’s model presented good linearity (R2 ≥ 0.999), indicating that such model can be applicable to analyze the systems. The n values for the pesticide release from hydrogels indicate that paraquat release has Fickian and non-Fickian diffusion, depending of hydrogel formulation. The values of k showed that the release of paraquat becomes slower when the MC and AAm concentration increases. Finally, to the best of our knowledge, we report a hydrogel-based vehicle (first carrier) that is able to prolong the sustained release of paraquat pesticide up to 45 days, which is essential for its application in controlled release systems.