Self-repairing bio-based controlled-release fertilizer for enhanced quality and nutrient utilization efficiency and reveal their healing mechanisms

Developing a bio-based membrane shell with excellent damage resistance and self-repairing capabilities is an effective strategy for enhancing the quality and efficacy of membrane-coated controlled-release fertilizers (CRFs). We present a simple and practical method to incorporate dynamic disulfide and hydrogen bonds into polyurethane to form a dynamic covalent network, which greatly improves the mechanical properties, damage resistance, and self-repair performance of polyurethane membrane shells. The novel membrane shell was coated on bio-based polyurethane CRF (BPCRF) to produce the self-repairing bio-polyurethane-coated CRF (SBPCRF). The SBPCRF product exhibited excellent controlled-release performance, and the nitrogen release life span increased by >50 % (by more than 20 days) than BPCRF. SBPCRF also exhibited remarkable damage resistance and exceptional self-repairing performance with a repair efficiency of 92.2 % at 25°C. Additionally, nitrogen release life span of the damaged SBPCRF can extended by 30 days than the damaged BPCRF. Furthermore, the membrane shell exhibited exceptional tensile elongation (1229 %) and tensile strength (5.271 MPa). The application of SBPCRF on maize also exhibited high nitrogen utilization (>60 %). Density-functional theory calculations indicated that the reorganization of dynamic disulfide bonds spontaneously occurred after breaking and then induced the responsible repair process of the material. This research provides insights into the development of coating materials that maintain the integrity of the membrane shell and ensure stable nutrient release throughout the crop life span and offers a novel strategy for the advancement of sustainable agriculture.