Preparation of Walnut wood-based lignocellulose-grafted with poly(ε-caprolactone) in DBU/DMSO /CO2 solvent system for slow-release nitrogen fertilizer

Due to the superior nutrient management and biodegradation properties, the biodegradable slow-release fertilizer shows a greater market prospect and environmental protection significance in the chemical fertilizer industry. In this study, a new kind of full bio-based slow-release fertilizers (B-SRFs) encapsulated by walnut wood-based lignocellulose-grafted with poly(ε-caprolactone) (WWL- g -PCL) in the presence of urea was prepared. Considering the multi-hydroxyl structural feature of walnut wood-based lignocellulose , WWL- g -PCLs were synthesized successfully through the ring-opening graft polymerization reaction (ROP) of walnut wood and ε-caprolactone in DBU/DMSO/CO 2 solvent system without adding additional catalyst. The structural and thermal characteristics of WWL- g -PCLs were thoroughly elucidated by nuclear magnetic resonance (NMR), fourier transform infrared spectroscopy (FT-IR), differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The results indicated that the WWL- g -PCLs exhibited favorable thermal properties with adjustable glass transition temperature (T g ) from 20.8 to 29.3 °C compared with walnut wood-based lignocellulose, which was beneficial for melt extrusion and granulation to produce B-SRFs. Scanning electron microscope (SEM), static release in water, and tomato fertilization efficiency experiments were conducted to delve into the slow-release mechanism and assess practical application effects. Subsequently, the outstanding slow-release performance of B-SRFs was observed for cumulative nutrient releases of 48–72% within 5 h in water and agreed with the Korsmeyer-Peppas model, indicating its excellent slow-release property. Furthermore, the formulated B-SRFs demonstrated a substantial increase in tomato cumulative biomass, yield, soil organic matter , and fertilizer utilization. Notably, there was a remarkable 57.8% increase in the cumulative biomass of tomatoes. These findings underscore the potential of walnut wood derivatives in developing effective and environmentally friendly slow-release fertilizers with promising agricultural applications.