Synergistic effect of La2O3 on the flame retardant properties and the degradation mechanism of a novel PP/IFR system

Abstract

The synergistic effects of lanthanum oxide (La2O3) on the thermal degradation and flame retardancy of a novel intumescent flame retardant polypropylene composites (PP/IFR) were investigated by the means of limited oxygen index (LOI), catalytic effectivity analysis (CAT-EFF), vertical burning test (UL-94), thermogravimetric analysis (TGA), cone calorimeter test (CCT), scanning electron microscopy (SEM), Laser Raman spectroscopy (LRS) and X-ray photoelectron spectroscopy (XPS). It was found that a small amount of La2O3 could enhance the LOI value of the PP/IFR composite dramatically and the materials can pass the UL-94 V-0 rating test. The catalytic effectivity (CAT-EFF) results showed that when 1wt.% La2O3 was added, it had the highest CAT-EFF, and could promote the LOI value of the composites from 27.1 to 32.5. The TGA data revealed that La2O3 could change the degradation behavior of the IFR and PP/IFR, enhance the thermal stability of the PP/IFR systems at high temperature and increase the char residue, especially in the air environment. The presence of La2O3 could change the decomposition behavior of the PP/IFR, and enhance the fire retardant performance, resulting consequently in a great reduction in peak heat release rate (p-HRR), total heat release (THR), smoke production rate (SPR) and total smoke production (TSP) of the PP/IFR system. The morphological structures observed by digital photos and SEM demonstrated that La2O3 could promote to form the more continuous and more compact intumescent char layer. The LRS measurements illustrated that the strength of the outer surface of the char residue with La2O3 is enhanced. The XPS analysis indicated that La2O3 can remain more O, N and P to enhance the strength of outer and inner char. Thus, a suitable amount of La2O3 plays an excellent synergistic effect with IFR on the flame retardancy, thermal degradation at high temperature, smoke suppression of IFR composites, and promotes the formation of compact char structures in the PP/IFR composites.