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 negligible solubility in available solvents, furthered by its non-biodegradable nature. Here in, a new sustainable approach for the unprecedentedly high dissolution (70 w/w%) and depolymerization of PU to low molecular weight (900 – 3000 g mol-1) depolymerized product is established. PU dissolves in deep eutectic solvents (DESs) comprising lactic acid (LA) and ZnCl2 under white light at 60 oC, and the dissolved material was regenerated using water. The multi-technique characterization of regenerated material evidenced the cleavage of urethane linkages and the emergence of new functional groups. The impact of change in DES component ratio on its efficiency towards dissolution and depolymerization of PU has highlighted the crucial role played by ZnCl2. The DESs have been reused where the properties of the regenerated material from recycled DES resemble those obtained from native DESs. The ease of PU processing via this environmentally friendly approach will encourage the development of new metal based DESs for processing of various 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.