Scalable glycolysis-based depolymerization of polyurethane foam waste enabled by ionic liquids

Abstract

We report a sustainable and scalable strategy for the chemical depolymerization of polyurethane foam waste (PUFW) by employing the ionic liquids (ILs) 1-n-butyl-3-methylimidazolium chloride ([Bmim][Cl]) and 1-n-butyl-3-methylimidazolium acetate ([Bmim][OAc]) as dual-function systems that act both as reactive media and efficient catalysts for the selective glycolysis of urethane bonds. Full depolymerization of PUFW is achieved under mild conditions (<100 °C, 1 atm) within 4–5 hours, offering a scalable alternative (up to 100 g of PUFW processing capability) to conventional glycolysis methods that typically require harsh thermal conditions (180–250 °C). The addition of water to the reaction medium enables the direct precipitation of the recycled polyol and allows for the efficient recovery and reuse of the water-miscible ILs [Bmim][Cl] and [Bmim][OAc], enhancing the sustainability of the process. The recycled product is then washed, dried, and analyzed by means of a solubility test in dimethyl sulfoxide (DMSO), the hydroxyl index (iKOH) value, nuclear magnetic resonance (NMR), and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Finally, the obtained recycled polyol is homogenized with the virgin polyol to synthesize new flexible polyurethane foams (FPUFs) that display identical physico-chemical and mechanical properties to the original FPUF. It should be noted that this glycolytic depolymerization process does not generate waste, since the complete mixture of reaction products is suitable for reuse as the starting material in the synthesis of new FPUFs. The active depolymerization medium is completely recoverable and can be reused for up to six operational cycles without any loss of catalytic efficiency, thereby demonstrating the recyclability and promoting the “greenness” of the process. Noteworthily, both the effectiveness and versatility of this process are also extended to the treatment of recalcitrant rigid PUFs (RPUFs), namely polyisocyanurate (PIR), highliting the versatility of this process, as well as its potential application on an industrial scale.