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

Zhang, Junhao, Kong, Qinghong, Yang, Lingwei, Wang, De-Yi
Green chemistry 2016 v.18 no.10 pp. 3066-3074
autoclaves, carbon, carbon monoxide, cobalt, cobalt oxide, fire hazard, green chemistry, heat, nanosheets, oxidation, pollution, polymer nanocomposites, polyurethanes, recycling, surfactants, thermoplastics, toxicity, value added
Huge consumption of thermoplastic polyurethane (TPU) results in two serious challenges for our society: fire hazards and environment pollution. To address these challenges, on the one hand, ultrathin β-Co(OH)₂ nanosheets were devised and synthesized by a surfactant self-assembly technique and their application in TPU reduced the fire hazard; on the other hand, 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 low thickness of ca. 2.6 nm, corresponding to the two layers of β-Co(OH)₂. The incorporation of ultrathin β-Co(OH)₂ nanosheets into the TPU matrix effectively reduced the heat release and restrained the toxicity of the volatiles, which was attributed to the ultrathin β-Co(OH)₂ nanosheets in the TPU matrix offering an enhanced barrier effect and catalytic charring capability and Co₃O₄ decomposed from β-Co(OH)₂ possessing superior catalytic oxidation of CO. Moreover, a green autocatalytic process in a 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 opens a new door to developing high performance polymer nanocomposites via green approaches and in particular, the sustainable recycling of the polymer-based materials.