Synergistic improvement of flame retardant properties of expandable graphite and multi-walled carbon nanotube reinforced intumescent polyketone nanocomposites

Flame retardant and self-extinguishing properties of composites are of importance to minimize heat release and smoke production during combustion for fire resistant polymer composites. This work presents intumescent flame retardant polyketone nanocomposites composed of multilayered expandable graphites incorporated with multi-walled carbon nanotubes. We observe a significant reduction of heat release rate, total heat release, and smoke production rate as the intumescent expandable graphites are introduced in the nanocomposites. A synergistic improvement of thermal stabilities such as high flame retardancy and self-extinguishing properties is found by adding a small amount of the carbon nanotubes in the composites, which is associated with the network formation between the carbon nanotubes and the expandable graphites, inhibiting the polymer degradation and evaporation of pyrolysis oil chars by carbonaceous chars formed during the combustion. The prediction of oxygen limited index of the expandable graphite and carbon nanotube reinforced nanocomposites is in good agreement with experimental results. Mechanical properties of the nanocomposites are investigated theoretically and experimentally to reveal the bridging effect of carbon nanotubes in the composites. We propose a possible mechanism for the synergistic improvement of the flame retardant behaviors of the nanocomposites to explain the interrelationship of thermal stabilities and network structures of the nanofillers.