Low Cost and Eco‐friendly Polymeric Matrix Prepared by Physical Cross‐linking As Potential Potassium Nitrate Release System

Chitosan-poly(vinyl alcohol) (PVA) blends were used to form spherical polymeric networks using sodium tripolyphosphate (STPP) as an ionic cross-linker. Ionotropic gelation and neutralization of protonated chitosan induced the formation of beads after contacting the polymeric droplets with a STPP aqueous solution. Morphology, structural characteristics and thermal stability of beads were elucidated using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and differential scanning calorimetry. The water swelling kinetics and the capacity of KNO3 loading of beads as well as the release process of the loaded salt were also studied. It was found that beads exhibited an equilibrium swelling ratio in the range of 324%-361%. PVA addition improved the economic viability of the polymeric matrix without compromising the formation of the beads. The cross-linking time and the composition of the polymeric hydrogel did not significantly modify the cross-linking degree and the fertilizer loading capability. Release experiments were performed submerging loaded beads in distilled water. After 10 days of continuous release, the cumulative concentration in the release medium reached near 100% of the initially loaded salt. Loaded beads are environmental-friendly and could be useful in agricultural applications as controlled-release fertilizers.