Few layered Co(OH)2 ultrathin nanosheets based polyurethane nanocomposites with reduced fire hazard: from eco-friendly flame retardance to sustainable recycling

Due to the huge consumption of thermoplastic polyurethane (TPU), it brings two serious challenges to our society: fire harzards and environment pollution. To address these challenges, on one side, ultrathin β-Co(OH)₂ nanosheets were devised and synthesized by surfactant self-assembly technique and its application in TPU reduced the fire hazards; on the other side, a green method was developed to sustainably recycle TPU nanocomposites into high value-added carbon materials. The structural characterizations demonstrate that the ultrathin β-Co(OH)₂ nanosheets showed a typical two-dimensional lamellar morphology, possessing a lateral dimension of ca.2 µm and a thin thickness of ca. 2.6 nm, corresponding to two layers of β-Co(OH)₂. The incorporation of ultrathin β-Co(OH)₂ nanosheets into TPU matrix effectively reduced the heat release and restrained the toxicity of the volatiles, which was attributed to that the ultrathin β-Co(OH)₂ nanosheets in TPU matrix enhanced barrier effect and catalytic charring capability, and decomposed to Co₃O₄ possessing superior catalytic oxidation of CO. Moreover, a green autocatalytic process in sealed autoclave was developed to convert TPU/Co(OH)₂ nanocomposites into high value-added Co/CNTs nanocomposites with more than 85% yield. This innovative idea may be expanded to other polymer systems and open a new door to developing high performance polymer nanocomposites via green approaches, and sustainable recycling of the polymer based materials in particular.