Macromolecular Nitrogen-Phosphorous Compound/Expandable Graphite Synchronous Expansion Flame Retardant Polystyrene Foam

A macromolecular nitrogen-phosphorous flame retardant combined with expandable graphite (EG) was employed to flame-retard expanded polystyrene foam. As the intumescent char formation (catalyzed by the flame retardant) temperature overlaps with the expanding temperature of EG, their synchronous expansion occurs. In this process, the EG sheets can be embedded in the intumescent char and pushed forward to the surface with inflation of the composite chars, which greatly enhances the compactness and strength of the char layer, and better shields the heat and oxygen, as well as promotes the interactions of the degraded products of the polymer and the flame retardant. The limiting oxygen index (LOI), vertical flame and cone calorimeter tests showed that good flame retardance for the flame retardant EPSF could be achieved (LOI: 33.9%, UL94-V0 (1.6 mm) and remarkably decreased heat release rate). A series of characterizations-including char morphology observation scanning by electron microscope, surface elements determination through X-ray photoelectron spectroscopy, char strength test and thermogravimetric analysis-were performed to verify the synergistic mechanisms based on the synchronous expansion of the composite chars.