A sustainable strategy: Nano-enhanced bio-based polyurethane coating with optimized hydrophobicity for efficient controlled release of fertilizers

Bio-based polyurethanes can effectively replace petrochemical polyurethanes in the development of coated fertilizers and have become a research hotspot. However, due to their strong hydrophilicity and low density, bio-based polyurethanes often result in excessively rapid nutrient release from coated fertilizers, which fails to meet practical application requirements. In this study, polycarbonate propylene carbonate diol (PPCD) and castor oil (CO) were used to form a co-soft segment, constructing an interpenetrating network structure to enhance the density of the membrane shell. Concurrently, an oleic acid-based hydrophobic agent was synthesized via a click chemistry reaction to modify halloysite nanotubes (HNTs), resulting in superhydrophobic HNTs with a contact angle of 153°. Subsequently, two types of hydrophobically modified controlled-release coated fertilizers were prepared using outer-layer nano-mixing and nano-spraying processes. The results indicated that the synergistic modification using PPCD and superhydrophobic nanotubes significantly improved the hydrophobicity and controlled-release performance of the coated fertilizers. Notably, under a coating rate of 4 %, the fertilizer prepared through the outer-layer nano-spraying process exhibited a longer nitrogen release period, demonstrating a substantial enhancement in the controlled-release performance of bio-based coated fertilizers. Therefore, this study provides a novel strategy for the development of highly efficient controlled-release bio-based coated fertilizers. • Superhydrophobic halloysite nanotubes were synthesized using oleic acid. • Preparation of two types of hydrophobic modified bio-based coated fertilizers. • The compactness and hydrophobicity of PCU have been significantly enhanced. • The surface of SPPCU exhibited significant hydrophobicity (WCA = 142°). • SPPCU has excellent controlled-release performance.