Effect of metallic oxides in polypropylene composites containing melamine phosphate and pentaerythritol

Abstract

The effect of metallic oxide in the intumescent flame retardant (IFR) polypropylene (PP) composites containing melamine phosphate (MP) and pentaerythritol (PER) is studied. The flammability of the composites was characterised by limiting oxygen index (LOI), UL-94 and cone calorimeter tests. It is found that, in the case of the IFR composites containing metallic oxides, all of them have higher LOI values than the composites without them, and composites with 1% zirconium dioxide (ZrO₂) or 1% dichromium trioxide (Cr₂O₃) can achieve the V-0 rating. The cone calorimeter results show that the composite containing 1%Cr₂O₃ has a lower heat release rate than the IFR composite, and the incorporation of titanium dioxide (TiO₂), lanthanum trioxide (La₂O₃), zirconium dioxide (ZrO₂) and Cr₂O₃, leads to a major decrease in the peak CO emission. Scanning electron microscopy reveals that the surface of the intumescent char is strongly modified in the presence of the metallic oxide. Moreover, the mechanical properties of the composites and the intumescent chars are studied.