Self-healing lignin-based coating for controlled-release fertilizers with enhanced damage resistance and stable nutrient release

A lignin-based polyurethane coating with self-healing ability was developed. • Dynamic disulfide bonds reduced coating porosity and improved toughness. • Nutrient-release period of controlled-release fertilizers was extended by 20 days. • The coating maintained release performance even after damage via self-repair. • Molecular simulations revealed optimal self-healing at a modifier content of 4.37%. Lignin is the second most abundant biomass resource in the world; it contains abundant active groups and has great application potential as a coating in controlled-release fertilizers (CRFs). However, lignin-based coatings are porous and vulnerable to damage. Herein, dynamic disulfide bonds were introduced into a lignin-based polyurethane network, increasing the interpenetrating crosslinking density of the network and reducing its porosity, which improved the damage resistance and self-healing performance of the coating. Specifically, the porosity of the lignin-based coating was reduced by 10.98% and the controlled-release period of encapsulated fertilizer was extended by 20 days (from 32 to 52 days) after disulfide-bond introduction. After the wear test, the lignin-based coating without disulfide bonds was almost completely damaged and lost its controlled-release capability, whereas the lignin-based coating with disulfide bonds remained intact, showing release behavior comparable to that of the unworn one. Additionally, cut lignin-based coating with disulfide bonds showed ∼12 days longer nutrient release than cut lignin-based CRFs. Finally, correlation between the self-healing modifier content, interfacial adhesion energy, and self-healing efficiency was investigated using molecular simulations. At a modifier content of 4.37%, the interfacial adhesion energy between the coating interfaces was 209.25 kcal/mol, and the repair efficiency reached the maximum value (44.16%). This study delivers useful theoretical insights into the high-value utilization of lignin and the creation of novel bio-based CRFs. Download: Download high-res image (236KB) Download: Download full-size image