Char Barrier Effect of Graphene Nanoplatelets on the Flame Retardancy and Thermal Stability of High-Density Polyethylene Flame-Retarded by Brominated Polystyrene

Graphene nanoplatelets (GNPs) with the char barrier effect were combined with brominated polystyrene (BPS) and antimony trioxide (Sb2O3) to improve the flame retardancy and thermal stability of high-density polyethylene. Thermogravimetric analysis, limited oxygen index (LOI) testing, and vertical burning testing (UL-94) showed that the presence of GNPs led to enhanced thermal oxidation stability and significantly reduced the flammability. The addition of 1 wt % GNPs to polyethylene/BPS-Sb (mass ratio=92/6/2) led to UL-94 grades from NG (first burning time>30 s) to V-2 (total burning time=14 s), and the LOI value increased from 23.4 to 24.1%. The results of the pyrolysis products provided evidence that the GNPs restricted volatilization. The morphology of the chars also proved the formation of the char layer, which could act as a barrier to isolate the material from the flame and retard the vaporization of flammable gases via a tortuous pathway. (c) 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40520.