Preparation of hydroxy-terminated polydimethylsiloxane and nano-SiO2 hydrophobic polyurethane coated urea and investigation of controlled nitrogen release

Abstract

In the present study, we successfully developed hydroxy-terminated polydimethylsiloxane (PDHT) and nano-SiO2 hydrophobic polyurethane-coated urea by applying the optimal conditions for hydrophobic polyurethane preparation. The hydrophobic polyurethane membrane material undergoes a comprehensive characterization. Infrared analysis confirmed the successful grafting of PDHT onto the polyurethane membrane material. X-ray Photoelectron Spectroscopy (XPS) and Energy Dispersive X-Ray Spectroscopy (EDX) analysis verify the even distribution of silicon on the surface of the membrane material. By Scanning Electron Microscopy (SEM) comparison, we elucidate the micro-structural disparity between the unmodified and modified castor oil-based polyurethane, accounting for the micro-level performance enhancement. The resulting modified membrane exhibited a water contact angle of 133.6°, indicative of its hydrophobic nature. The optimal ratios for PDHT and nano-SiO2 were determined to be 16 % and 2 %, respectively. Notably, hydrophobic polyurethane-coated urea demonstrated an extended-release period of 98 days (5 % coating amount), a 40 % improvement over its unmodified counterpart. In addition, the silicone-modified coated urea reduced the amount of ammonia volatilization by about 76.32 %, which plays a significant role in enhancing fertilizer utilization efficiency and is important for ecological environment protection. This research provides a straightforward and efficient way to fabricate slow-release fertilizers, with significant implications for the advancement of coated slow-release fertilizer technology.