Polyurethane nanocomposites can increase the release control in granulated fertilizers by controlling nutrient diffusion

Abstract

We proposed a nanocomposite system based on castor oil-derived polyurethane (PU) for controlling the release of fertilizers by an ion-exchange mechanism. PU coatings modified with less than 5% montmorillonite, a cation-exchange material, successfully retarded the nitrogen release from urea granules, with less than 50% of the nutrient released within 18 days of immersion, as confirmed by soil incubation experiments. The same profile was observed for the phosphate release from monoammonium phosphate (MAP) granules coated with PU modified with hydrotalcite (less than 5% by weight), an anion-exchange material. The release times were proportional to the contents of the cation- or anion-exchange materials, which exhibited specific correlations with the kind of nutrient released (i.e., cationic or anionic), confirming the diffusion barrier promoted by the PU coating structures. Our results demonstrated that the use of PU nanocomposites can significantly reduce the coating thickness with improved nitrogen and phosphorus release control, opening a new field for the investigation of controlled release fertilizers.