Recovery of multiple polyol grades from complex flexible polyurethane foams by depolymerization with alkanolamines

The chemical recycling of polyurethane (PU) foams is limited by their chemical complexity, especially in multi-polyol formulations, resulting in low recovery rates of high-value products. This study presents a novel chemical depolymerization approach using diethanolamine (DEA) to achieve three-phase separation and maximize recovery of aromatic amines derived from isocyanates. Reaction parameters including temperature, reaction time, and DEA:PU ratio were evaluated, identifying optimal conditions (240 °C, 30 min, DEA:PU 2:1 by mass) that consistently produced a clear three-phase separation and yielded methylenedianiline (MDA) at 89 % of the theoretical maximum. Layer analysis revealed a distinct component distribution: the top and middle phases contained mainly polyols (82.7 % Polyol 1, 87.4 % Polyol 2, respectively), while the bottom phase was predominantly MDA and unreacted DEA. Urea-containing intermediates formed under milder conditions, gradually decomposing into aromatic amines under extended reaction times, revealed aminolysis as the dominant reaction pathway. The method was successfully applied to MDI- and TDI-based foams, with up to five polyols, and to mixed foams, demonstrating robustness and versatility. A predictive test, mixing polyols and cleaving agents at room temperature, reliably indicated the feasibility of three-phase separation even before depolymerization. Testing other cleaving agents showed that alkanolamines with primary or secondary amines, such as 2-aminoethanol, can also induce three-phase separation. The potential of other amines requires further investigation for optimized and efficient macroscopic phase separation.