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 (GODOPO) by using a silane agent [(3-glycidyloxypropyl)trimethoxysilane] as the chemical bridge. Then the GODOPO 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.

Automated summary

By synthesizing a DOPO derivative and grafting it onto the surface of graphene oxide, and then mixing with TPU by melt compounding, the flame retardancy of TPU was improved while maintaining its ductility. The addition of GO-DOPO significantly reduced the heat release rate and smoke production rate of TPU, enhancing the fire safety of the material.