Recyclable and removable functionalization based on Diels-Alder reaction of black phosphorous nanosheets and its dehydration carbonization in fire safety improvement of polymer composites

Based on reversible Diels-Alder reaction, we herein precisely control the formation and elimination of surface functionalization composed of triallyl isocyanurate for black phosphorous (BP) nanosheets, at different reaction temperatures. Direct TEM observation, FTIR spectra, and XPS test confirm that this surface functionalization is capable of firstly covering onto the surface of BP nanosheets and then removed. This surface functionalization not only improves the interfacial interaction between BP nanosheets and polymer matrix, but also converts BP nanosheets into phosphorus pentoxide and phosphoric acid owning dehydration carbonization effect. As a result, cone calorimetric test demonstrates that incorporating 2.0 wt% functionalized BP nanosheets strikingly decreases the peak heat release rate (PHRR) and total heat release (THR) of thermoplastic polyurethane (TPU) by 61.6% and 56.7%, respectively. Such a novel strategy simultaneously improves the flame retardancy, solves the contradiction between high crystal purity and surface functionalization, and offers recycle capsulation method for BP nanosheets.