Preparation and Properties of Bio-Based Polyurethane Controlled Release Urea Coating with Photosensitivity

In order to improve the photodegradation ability of fertilizer coating material and realize the sustainability of fertilizers, in this study, the commercially available photosensitive iron stearate (FeSt₃) was wet-ground into submicrometer FeSt₃ (SFeSt₃) particles and used in preparation of a SFeSt₃-modified bio-based polyurethane (PU)-coated controlled release urea (PU-SFe-CRU). The results showed that after 1 month photodegradation, the coating material had significant yellowing, the oxygen content of SFeSt₃-modified PU (PU-SFe) increased by 56.89%, and its structure became more porous and looser than PU. The thermal stability of PU-SFe decreased, and more intermediate products were produced after exposure to UV light. The germination experiment showed that PU-SFe before and after photodegradation (up to 60 mg/L) had no adverse effect on the seed germination and bud growth of rice. Additionally, PU-SFe had a significantly higher Cr adsorption capacity after photodegradation due to the increase of the oxygen-containing group and specific surface. This study provides a theoretical basis for the research and development of photodegradable environment-friendly controlled release urea.