Interface engineering of graphene oxide containing phosphorus/nitrogen towards fire safety enhancement for thermoplastic polyurethane

The high flammability and generation of toxic volatiles during combustion are big obstacles for thermoplastic polyurethane (TPU). In this work, a 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivate containing phosphorus and nitrogen was synthesized and then grafted onto the surface of graphene oxide (GO-DOPO) by using a silane agent [(3-glycidyloxypropyl)trimethoxysilane] as the chemical bridge. Then the GO-DOPO was mixed with TPU by melt compounding to improve its flame retardancy. Tensile tests exhibited that the TPU/GO-DOPO nanocomposite maintained high ductility with a slight increase in tensile stress. The cone calorimeter tests exhibited that the incorporation of 2 wt% GO-DOPO into TPU presented a significant reduction in peak heat release rate (35.8%) and peak smoke production rate (50%), respectively, as compared with those of pure TPU. Meanwhile, the peak of CO production rate and the peak of CO₂ production rate decreased by 57.1% and 35.9%, respectively. The investigation of the flame retardant mechanism for TPU nanocomposites revealed that the presence of GO-DOPO in TPU contributed to generating the compact, continuous and higher graphitized char layer exerted barrier effect in condensed phase, protecting the underlying TPU matrix. This work provides a feasible functionalization approach of GO to enhance the fire safety of TPU nanocomposites without sacrificing the superior mechanical properties, which facilitates the promising applications of TPU in various fields.