Influence of microencapsulated red phosphorus on the flame retardancy of high impact polystyrene/magnesium hydroxide composite and its mode of action

Abstract

A series of high impact polystyrene/magnesium hydroxide/microencapsulated red phosphorus (HIPS/MH/MRP) composites with identical total loading of flame retardant and different loadings of MRP were prepared by melt compounding. The influence of MRP on the flame retardancy of the HIPS/MH composite and its mode of action were investigated by limiting oxygen index, UL-94, cone calorimeter test, thermal analysis, scanning electron microscopy, X-ray diffraction and Fourier transform infrared. It is shown that the introduction of suitable amount of MRP can increase the thermal stability and flame retardancy of the HIPS/MH composite significantly. When the mass fraction of flame retardant in the HIPS/MH/MRP composite is fixed at 33.3 wt% and MRP accounts for around 10 wt%, the composite can reach V-0 rating and have the largest LOI value of 24.2%, exhibiting optimal comprehensive fire retardancy. The composite with 4 wt% MRP has the smallest heat release rate, total heat release and average effective heat of combustion. The flame retardant effect of the HIPS/MH/MRP composite occurs mainly in the gas phase at low MRP loading. Because of the porous and incompact degradation residue and large heat release rate and total heat release, the composite with excessive MRP exhibits notable decrease in flame retardancy.