Starch-Chitosan Hydrogels for the Controlled-Release of Herbicide in Agricultural Applications: A Study on the Effect of the Concentration of Raw Materials and Crosslinkers

Present work aims to synthesize the herbicide-loaded bio-based hydrogels and study the release mechanism. The different ratios of starch and chitosan were chosen as the bio-based resources to form the hydrogel matrix with varying concentrations of two crosslinkers. The synthesized hydrogels were characterized using Fourier transform infrared spectroscopy for reaction completion. Thermogravimetric analysis provided information about the obtained hydrogels’ thermal stability, suggesting the tremendous positive impact of chitosan concentration. Differential scanning calorimetry was done to know the initial trapped water release from the hydrogel matrix and relate the structures with the release rate study. Further, scanning electron microscopy revealed the morphology of the obtained hydrogels and could establish the relation with the corresponding hydrogel structures. The equilibrium swelling degree, release dynamics of atrazine, and diffusion mechanism have also been evaluated. The swelling significantly affected the release behavior, and the hydrogels prepared with glyoxal showed the lowest release rate of atrazine, the release vitality reaching 500 h. Until the concentration of starch and chitosan were equal, release followed the Fickian diffusion mechanism, and as soon as the concentration of chitosan increased, non-Fickian diffusion proceeded.