Synergistic effects of mono-component intumescent flame retardant grafted with carbon black on flame retardancy and smoke suppression properties of epoxy resins

A mono-component intumescent flame retardant named pentaerythritol phosphate melamine salt (PPMS) was grafted on the surface of carbon black (CB) to obtain PPMS-grafted CB (PPMS-CB). The obtained PPMS-CB was well characterized and then incorporated into epoxy resins (EPs) to investigate flame retardancy and smoke suppression properties. Thermo-gravimetric analysis indicates that the synergism between PPMS and CB could improve the char-forming ability of EP composites. Limiting oxygen index (LOI) and UL94 vertical burning tests reveal that EP composite with 15 mass% PPMS-CB achieves a LOI value of 26.2% and passes the UL94 V-1 rating, while the same addition of PPMS only achieves a UL94 V-2 rating and LOI value of 22.7%. Cone calorimeter and smoke density tests show that the incorporation of PPMS-CB obviously decreases the heat release and smoke production of EPs, for example, 66.9% reduction in peak heat release rate, 54.3% reduction in peak smoke production rate and 36.5% reduction in smoke density rating, are observed in the case of EP composite with 15 mass% PPMS-CB. The excellent performance of EP/PPMS-CB composites can be ascribed to the formation of more cross-linking structures containing N and P in the condensed phase, thus producing a more compact and continuous char that acts as a thermally stable barrier against the heat and mass transfer. Overall, the chemical combination of PPMS and CB provides a new approach to develop highly efficient mono-component intumescent flame retardant and corresponding super flame-retarded polymer materials.