Controllable release fertilizer with low coating content enabled by superhydrophobic castor oil-based polyurethane nanocomposites prepared through a one-step synthetic strategy

Although the inherent degradability and sustainability of bio-based polymers make them promising coating candidates for controlled-release fertilizer (CRFs), large amounts of coating materials (coating content usually above 5%) and complex modification process are usually required to achieve controllable-release characteristics, which increases the production costs and therefore limits their application. In this study, superhydrophobic castor oil-based polyurethane/carbon black nanocomposites was developed through a one-step synthetic strategy to synthesize CRFs with low coating content by a three-layer rotating-drum coating method. The effect of the carbon black content and layer distribution on contact angles, physicochemical properties, microstructure, and release characteristics of the resulting coating material and CRFs was characterized and discussed. The contact angle of the polyurethane nanocomposites can reach up to 152.6°. In addition, the N release longevity of the coated urea fertilizer was extended to 30 days, definitely meeting the standards for CRFs using low coating content of 3 %. The coated fertilizers presented Super Case II transport mechanism. The mechanism underlying the controlled-release of this coated fertilizer was explored and discussed. The technique reported here offers a number of advantages, including low cost, easy performance, and excellent controllable-release performance, opening numerous opportunities for widely application of this environmentally-friendly, green CRF.