Poorly-/well-dispersed graphene: Abnormal influence on flammability and fire behavior of intumescent flame retardant

Surface feature of ammonium polyphosphate is modified by cation exchange reaction with piperazine, and then reduced graphene oxide nanosheets are attached to the surface of modified flame retardant via hydrogen bonding interactions. Good dispersion of graphene in the polypropylene matrix is observed. The dispersion state of graphene has an abnormal effect on the flammability results under small flame and fire behavior under forced flaming condition of intumescent flame retardant (IFR) composites. The well-dispersed graphene results in significantly deteriorated limiting oxygen index and UL-94 rating. The graphene with good dispersion is adverse to flammability results, which is in contrary to the widely-acknowledged flame retardant mechanisms. Low content of well-dispersed graphene exhibits higher reduction effect on heat release than that of poorly-dispersed counterpart. Novel flame retardant mechanism and model are proposed and new understanding of the role of graphene in the combustion of IFR is provided.