Closing the Loop on Polyurethane Foam Waste: Challenges, Emerging Technologies, and the Road to Sustainable Circularity.

The increasing production of polyurethane foams (PUFs) and their inherently cross-linked, recalcitrant structure pose major challenges for waste management and circular economy implementation. While mechanical recycling remains the preferred option for thermoplastics, its applicability to thermoset materials such as PUFs is severely limited. Chemical depolymerization has therefore emerged as a key strategy for closing the loop on PUF waste (PUFW). This review provides a critical overview of the chemistry, mechanisms, and technological readiness of the main chemical recycling pathwaysparticularly glycolysis and acidolysishighlighting their reaction dynamics, process parameters, and environmental implications. Glycolysis stands out as a mature and versatile technology capable of recovering high-purity polyols under optimized catalytic conditions, whereas acidolysis using (di)-carboxylic acids offers milder operation, faster kinetics, and reduced release of toxic aromatic amines. Hybrid processes that combine both approaches are now entering industrial deployment, as demonstrated by large-scale consortia, such as Renuva, Circufoam, and Recpur, which collectively illustrate the progression from laboratory research to pilot-scale or commercial implementation. Additionally, emerging biotechnological routesencompassing enzymatic depolymerization and nonisocyanate polyurethane synthesisand Dynamic Covalent Polymer Networks (DCPNs) approaches are discussed as complementary long-term solutions, though they remain at low technology readiness levels (TRL < 4). Overall, this review identifies the current advances, limitations, and prospects of PUF chemical recycling technologies and provides a roadmap for integrating these strategies into sustainable polymer value chains within a truly circular economy framework.