Synergistic flame-retarded effect between carbon nanotubes and ammonium polyphosphate in Nylon6 and Nylon6/polystyrene blends

The association of carbon nanotubes (CNTs) and ammonium polyphosphate (APP) as flame retardants was utilized for improving the flame retardancy of nylon6 (PA6) and blends of PA6/Polystyrene (PS). A remarkable synergistic effect between APP and CNTs was observed in PA6 at 1-wt% CNTs loading. Rheological tests showed that 1-wt% CNTs formed a network structure. Morphology of residue char indicated that a network enhanced synergistic effect. A synergy between APP and CNTs in blends of PA6/PS (56/24) was also investigated. APP and CNTs exhibited a remarkable synergistic effect at 0.25-wt% CNTs loading, but the antagonistic effect on flame retardancy of blends was observed at 1-wt% CNTs loading. Transmission electron microscopy showed that CNTs were exclusively dispersed in the PA6 phase of blends. The selective dispersion of CNTs caused the formation of a network at 0.25-wt% CNTs loading. Morphology of residue char indicated that 0.25-wt% CNTs were benefited by the formation of a continuous and well-swollen residue char that enhanced the synergistic effect in blends. However, the aggregation of 1-wt% CNTs in PA6 phase caused high viscosity of PA6 phase, resulting in a poor expansion of the residue char. Consequently, the antagonism was exhibited.