Effects of the addition of carbon black on the carbonization and flame retardancy of polypropylene in combination with nickel–molybdenum–magnesium catalysts

Carbon black particles were incorporated into the polypropylene (PP) in combination with Ni–Mo–Mg catalysts to investigate their influences on the carbonization and flame retardancy of PP. The results demonstrate that the carbon black exhibited a very positive effect on the char yield of PP in a pyrolyzation experiment with different temperatures. For pyrolyzation at 750 and 550°C, the PP/5% Ni–Mo–Mg/5% carbon black blends gave 56 and 37.1% char yields, respectively. Scanning electron microscopy, transmission electron microscopy results, and direct optical observations from designed experiments all demonstrated a combination of carbon black with growing carbon nanotubes (CNTs) for the generation of char with integrated and compact structures. Cone calorimeter and limited oxygen index tests confirmed that the integration of carbon black particles and CNTs led to a significant improvement in the flame retardancy of PP.