Unprecedently high dissolution and depolymerization of hard-to-dissolve polyurethane in deep eutectic solvents under low-energy white light

Abstract

Polyurethane (PU), a synthetic polymer, is of immense commercial use. However, its utility and processing are limited by its negligible solubility in available solvents and by its non-biodegradable nature. Herein, a new sustainable approach for the unprecedentedly high dissolution (70 w/w%) and depolymerization of PU to a low-molecular-weight (900–3000 g mol⁻¹) depolymerized product is established. PU is dissolved in deep eutectic solvents (DESs) comprising lactic acid (LA) and ZnCl₂ under white light at 60 °C, and the dissolved material was regenerated using water. The multi-technique characterization of the regenerated material evidenced the cleavage of urethane linkages and the emergence of new functional groups. The impact of changes in the DES component ratio on its efficiency towards dissolution and depolymerization of PU highlighted the crucial role played by ZnCl₂. The DESs have been reused, and the properties of the regenerated material from recycled DES resemble those obtained from native DESs. This environmentally friendly approach simplifies PU processing and is expected to encourage the development of new metal-based DESs for handling a variety of non-biodegradable and hard-to-dissolve polymers. Further, reusability of DESs is expected to elevate the benefit-cost ratio to 15.723, making this process economically viable and attractive for industrial use.