Bio-based non-isocyanate polyurethane with closed-loop recyclability and its potential application

Developing bio-based non-isocyanate polyurethanes (NIPUs) to replace petroleum-based conventional polyurethanes (PUs) plays an essential role in green production and relieving energy pressure. However, the synthesis of NIPUs using renewable resources, and recycling after reaching service time remain to be solved. Herein, a novel structural cross-linked NIPU network with closed-loop recyclability was prepared, which is derived from abundant lignin-derived and carbon dioxide (CO2) resources. The obtained NIPUs with dual dynamic covalent bonds exhibit relatively low activation energy (70.34 kJ/mol) and remarkable remolding efficiency (∼100 %). Importantly, spiro bi-acetal structures in polymer chains impart closed-loop recyclability to the obtained NIPUs. The results showed that they can be degraded at room temperature followed by regeneration with nearly full recovery of properties. Moreover, bio-based NIPUs are used as supporting materials to produce phase change materials (PCMs) for the first time, and the latent heat reaches 128.2 J/g. The material has favorable form stability and is leakage-proof owing to ZnⅡ-carboxylates coordination interactions and stable cross-linked networks. This study demonstrates a method for the synthesis of closed-loop recyclable NIPUs from renewable resources, enriching synthetic diversity while providing an initial exploration of its potential as PCMs.