Synergistic Surface Engineering of Sustainable Polyurethane: Flame Retardancy, Kinetics, and Multiphase Oil Adsorption Perspectives

Abstract Severe threats posed by oil spill incidents to aquatic ecosystems have increased the demand for green, circular, and sustainable materials to mitigate these problems. Biobased polyurethane sponge (BS) derived from renewable resources serves as an excellent candidate; however, the inherent flammability and poor hydrophobicity hinder its practical use in oil spill remediation. Herein, we introduce a multifunctional surface modification approach for these matters. A coating containing reduced graphene oxide (RGO), diammonium hydrogen phosphate (DAP), and stearic acid (SA) was applied to BS to fabricate the modified sponge (BS-RDS). This modification imparted the BS with self-extinguishing behavior and markedly enhanced its flame retardancy; notably, a UL-94 V-0 rating was achieved when the BS was coated with a 10 wt % DAP solution. In parallel, the surface hydrophobicity of the modified BS was significantly improved, with an increase in the water contact angle to 134°. Moreover, the BS-RDS demonstrated effective oil adsorption capacities ranging from 11 to 40 g/g, depending on oil type, and retained 7–9 times its own weight after 10 cycles. The adsorption of different oils followed distinct multistep mechanisms, with their adsorption rates being determined by their respective physicochemical properties. These results demonstrate a sustainable solution for oil spill remediation.