Influence of nanoparticle geometry on the thermal stability and flame retardancy of high-impact polystyrene nanocomposites

Nanocomposites of high-impact polystyrene (HIPS) with three types of nanoparticles, namely layered organically modified montmorillonite (OMMT), tubular multi-walled carbon nanotubes (MWNTs) and spherical silica nanoparticles, were prepared by melt blending method. The influence of nanoparticle geometry on the thermal stability and flame retardancy of HIPS nanocomposites was investigated by transmission electron microscopy, thermo-gravimetric analysis, cone calorimeter method and scanning electron microscopy. The results show that the presence of three types of nanoparticles with varying geometries does not change the degradation mechanism of the nanocomposites, but greatly decreases the heat release rate and mass loss rate of the materials due to the fire residue formed in the condensed phase. The layered structure of OMMT exhibits the best flame-retarded effect, and the tubular structure of MWNT obtains a weaker flame-retarded effect and the spherical structure of silica nanoparticles the weakest. The effectiveness of flammability reduction is varied with nanoparticle geometries due to the discrepancies in featured structures of fire residues formed in real fire conditions. The idealized models of the featured structures of fire residues from the nanocomposites studied are put forward to explain the flame-retardant mechanism of the nanoparticles with different geometries.