Controlled Aminolysis of Multilayer Polyurethane Composites for Sustainable Upcycling into Waterborne Polyurethane Emulsions

The effective chemical recycling of polyurethane (PU) waste remains a critical challenge due to its crosslinked structure and frequent integration into multilayered composites. Herein, we report a controlled aminolysis strategy using diethanolamine (DEA) at 130 °C to selectively cleave urethane bonds and recover functional oligomers from diverse industrial PU wastes, including foams, elastane blends, and PU-coated textiles. A simple pretreatment enables intact separation of PU layers from textile substrates, followed by depolymerization and liquid–liquid extraction to yield phase-separated oligomers with distinct molecular weights and end-group functionalities. Without requiring complete depolymerization into monomers, the organic phase oligomers were directly upcycled into waterborne polyurethane (WPU) emulsions by replacing 50% of the virgin polyol. Among the formulations, elastane-derived WPU (WPUE) exhibited superior emulsion stability closely matching that of a model polyol-based WPU, while foam- and coating-derived variants showed relatively lower performance. The resulting WPU emulsions had number-average molecular weights in the range of 15–20 kg/mol and solid contents exceeding 35 wt.%, making them suitable for high-performance functional coatings. To demonstrate practical applicability, WPUE was applied as a leather coating and compared with a commercial PU binder. Notably, WPUE showed higher adhesion strength than the commercial control, confirming its potential as a standalone sustainable coating material. This scalable and solvent-free process therefore enables selective upcycling of complex PU waste into functional WPU emulsions with direct industrial relevance, advancing circularity in polyurethane-based materials.