Conventional isocyanate-based polyurethane (PU) and polythiourethane (PTU) present challenges for green chemistry, sustainability, and the circular economy. First, isocyanates are toxic, with major negative implications for human health and the environment. Second, conventional PU is most often produced in network form, which disallows mechanical recycling via melt-state reprocessing because the permanent cross-links prevent melt flow. Here, in this Department of Energy funded study, we describe research in which we produce recyclable non-isocyanate PU (NIPU) in the form of polyhydroxyurethane (PHU) and non-isocyanate PTU (NIPTU) via simple one-step or two-step chemistry. As designed, our network-based PHUs and NIPTUs can be reprocessed in the melt-state multiple times with full recovery of cross-link density and associated properties. We also demonstrate that PHU networks can be made in the form of foams, which is a common product format for conventional PU networks. Additionally, we show that linear NIPTUs can lead to network formation during melt-state processing via self-activated dynamic covalent disulfide linkages. Finally, an important end-of-life option for NIPU, NIPTU, and PTU is monomer recovery. We will discuss the challenges associated with developing a general approach for monomer recovery for each of these classes of polymer and show positive results with monomer recovery as high as ~50% for at least one of these materials.

Chemical recycling of non-isocyanate polyurethane and polythiourethane: Monomer recovery from networks and linear polymers and recovery of network cross-link density after reprocessing

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ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.