Ternary Synergistic Catalysis Enables Mild Solvent-Free Closed-Loop Upcycling of Polyurethane Foam

Abstract

Efficient recycling of polyurethane foam (PUF) under mild conditions remains a critical challenge. Herein, we report a ternary 1,1,3,3-tetramethylguanidine (TMG)/cadmium (Cd)/1-methyl-2-hydroxymethylimidazole (HMMI) catalyst with Cd as the metal center, integrating Brønsted base, Lewis acid, and binuclear metal. Combined with a multistage degradation strategy, it achieves complete cleavage of carbamate/urea bonds in PUF under solvent-free mild conditions (180–200°C, 4 h, degradant dosage: 10 wt% relative to PUF mass), enabling spontaneous phase separation into high-purity recycled polyols (RP) and isocyanate-derived hard segments (HS). RP exhibits properties similar to virgin polyols (VP) (hydroxyl value: 66 mgKOH g⁻¹; viscosity: 950 mPa s) and can replace 40 wt% of VP without compromising foam performance, while HS serves as a reinforcing additive for rigid foams. This closed-loop strategy minimizes waste, aligns with circular economy principles, and provides a scalable pathway for PUF upcycling.