Superior flame retardant by combining high aspect ratio layered double hydroxide and graphene oxide

By combining two platy nano-additives with high aspect ratio, a layered double hydroxide (LDH) and graphene oxide (GO), remarkable flame retardancy in polystyrene nanocomposite was observed. Surprisingly, the effect is superior to nanocomposites made with either of the two types of fillers. The nanocomposites were prepared via solution blending from tetrahydrofuran utilizing a three-roll mill for improved compounding. A highly stable suspension of a mixture of the two nano-additives in THF was achieved by sophisticated surface modifications of LDH and GO using 3,4-dihydroxybenzophenone (DBP) and 1-dodecylamine (DDA), respectively. Forced sedimentation tests and particle size distribution confirmed the good suspension and suggested that heterocoagulation between the two types of oppositely charged colloids could be prevented by the appropriate combination of surface modificators. Cone calorimetry revealed a significant reduction of the peak of heat release rate of 47% at a very low loading (5.5 wt%). Most interestingly, after formation of a protective layer, combustion occurred at a much reduced heat release rate, and consequently, the related burn out time was prolonged by 154%. While, as usual, these platy inorganic fillers fail to reduce time of ignition or improve limiting oxygen index, the pronounced push of the burn out time underlines the great potential resting in the combination of different types of adjuvant fillers. The remarkably reduced heat release rate for longer burning times is superior to other published nanocomposites. When combining this system with flame retardants decreasing total heat evolved and reducing the initial peak of heat release rate, very efficient flame retardant systems will be obtained.