Combined effect of transition metal phosphide (MxPy,M = Ni,Co, and Cu) and intumescent flame retardant system on polypropylene

In this paper, three typical transition metal phosphide nanocrystallines (M_xP_y, M = Ni, Co, and Cu) were synthesized by a novel hydrothermal method, and their structures were characterized by X‐ray diffraction and transmission electron microscopy. Then they were used as synergistic agents with intumescent flame retardant (IFR) to improve the fire safety of polypropylene (PP). Thermogravimetry analysis (TGA) results indicated that the introduction of these synergists could improve the thermal stability and char yields of the PP/IFR system. The addition of 2 wt.% Ni₁₂P₅ and Co₂P increased the limiting oxygen index values of the PP/IFR system significantly from 28% to 36% and 34%, respectively, and the system could reach V‐0 rating. The cone calorimeter test results revealed that the combination of transition metal phosphide nanocrystallines and IFR system could result in excellent flame retardancy. The incorporation of these synergists into IFR led to a remarkable influence on charring of PP composites as revealed by TGA and cone data. The morphological structure of char residue proved that the addition of transition metal phosphide nanocrystallines was capable of forming a compact and homogeneous char on the surface, which turned out to be of most importance for the flame retardancy. Thermogravimetric analysis/infrared spectrometry results indicated that the flame retardant mechanism of PP/IFR/M_xP_y (M = Ni, Co, and Cu) system was in the condensed phase rather than in the gas phase. Copyright © 2014 John Wiley & Sons, Ltd.