Effect of carbon black on the thermal degradation and flammability properties of flame-retarded high impact polystyrene/magnesium hydroxide/microencapsulated red phosphorus composite

Nanosized carbon black (CB) was introduced to flame-retarded high impact polystyrene/magnesium hydroxide/microencapsulated red phosphorus (HIPS/MH/MRP) composite by melt compounding. The effect of CB on the thermal degradation and flammability properties of the HIPS/MH/MRP composite was investigated by thermal analysis, limiting oxygen index (LOI), UL-94 vertical burning test, cone calorimeter test (CCT), and scanning electron microscopy (SEM). It is shown that the introduction of CB increases both the thermal and thermo-oxidative stability of the HIPS/MH/MRP composite. CB is very effective to hinder dripping of the HIPS/MH/MRP composite. The addition of just 0.7 wt% CB can increase the UL-94 rating of this composite from V-1 to V-0. CB almost has no influence on LOI and peak heat release rate of the composite in CCT, but the composite becomes more difficult to ignite after addition of CB. The HIPS/MH/MRP composite with CB tends to crack upon thermal degradation and burning. On the whole, the introduction of CB is conducive to the improvement of thermal and thermo-oxidative stability as well as flame retardancy of the HIPS/MH/MRP composite. Such improvement originates from crosslinking of polymer macroradicals on the surface of CB particles. The result of this work provides a practicable method to further enhance the thermal and fireproof properties of flame-retardant HIPS. POLYM. COMPOS., 39:770-782, 2018. (c) 2016 Society of Plastics Engineers