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. © 2016 Society of Plastics Engineers