Toward Circular Recycling of Polyurethanes: Depolymerization and Recovery of Isocyanates

Abstract

We report a depolymerization strategy to nearly quantitatively regenerate isocyanates from thermoplastic and thermoset polyurethanes (PUs) and then resynthesize PUs using the recovered isocyanates. To date, chemical/advanced recycling of PUs has focused primarily on the recovery of polyols and diamines under comparatively harsh conditions (e.g., high pressure and temperature), and the recovery of isocyanates has been difficult. Our approach leverages an organoboron Lewis acid to depolymerize PUs directly to isocyanates under mild conditions (e.g., ∼80 °C in toluene) without the need for phosgene or other harsh reagents, and we show that both laboratory-synthesized and commercially sourced PUs can be depolymerized. Furthermore, we demonstrate the utility of the recovered isocyanate in the production of second-generation PUs with thermal properties and molecular weights similar to those of the virgin PUs. Overall, this route uniquely provides an opportunity for circularity in PU materials and can add significant value to end-of-life PU products.

Influence of Carboxylic Acid Structure on the Kinetics of Polyurethane Foam Acidolysis to Recycled Polyol

“…PU chemical depolymerization can be driven by chemolysis using reactants such as water (hydrolysis), glycols/alcohols (glycolysis/solvolysis), acids (acidolysis), and amines (aminolysis) to break chemical bonds within the PU structure into monomeric or oligomeric units. PU chemical recycling schemes generally focus on recovery of polyol, although some recent studies have attempted to recover isocyanates as well . As of 2023, glycolysis and acidolysis have been commissioned on pilot or industrial scales, although neither have been widely commercialized. ,,− Acidolysis uses organic acids, typically dicarboxylic acids (DCAs), to break down PU materials into carbon dioxide (CO 2 ), recycled polyol (repolyol), and amides.…”