Opportunities in Closed-Loop Molecular Recycling of End-of-Life Polyurethane

Polyurethane (PU) is the sixth most used plastic. Total production reached 24 million metric tons in 2018 and continues to grow at an annual rate of 4%. As production increases, so does the accumulation of PU waste and the need to find a viable recycling method. However, due to the highly cross-linked structure and complex composition of postconsumer PU, mechanical recycling methods produce lower-value products with limited reusability. Chemical treatments that extract reusable components can offer alternative approaches to PU waste valorization. Chemical recycling of PU waste is underdeveloped given the significant potential economic and environmental impacts. Mechanistic studies on chemical recycling pathways, such as hydrolysis, acidolysis, glycolysis, and aminolysis, are incomplete, and few of these methods have been used commercially. This perspective provides an overview of several closed-loop chemical recycling methods that can be used to produce recycled polyol (repolyol) from waste PU, which can be used in place of virgin polyol. We delineate what is known regarding the chemistry and mechanisms, identify knowledge gaps, and compare the utility of the products from each recycling method. We also suggest ways that density functional theory can be used to fill knowledge gaps.