Synergistic effects of lanthanum oxide on a novel intumescent flame retardant polypropylene system

The effects of lanthanum oxide (La2O3) as a synergistic agent on the flame retardancy of intumescent flame retardant polypropylene composites (IFR-PP) were studied, and the new IFR system mainly consisted of the charring-foaming agent (CFA) and ammonium polyphosphate (APP). The limiting oxygen index (LOI), UL-94 test, thermogravimetric analysis (TGA), cone calorimeter (CONE) and scanning electron microscopy (SEM) were used to evaluate the synergistic effects of La2O3. It was found that when IFR was fixed at 20 wt% in IFR-PP composites, only a little amount of La2O3 could enhance LOI value and pass the UL-94 V0 rating test (1.6 mm). The TGA data showed that La2O3 could enhance the thermal stability of the IFR-PP systems at high temperature and effectively increase the char residue formation. The CONE results revealed that La2O3 and IFR could clearly change the decomposition behavior of PP and form a char layer on the surface of the composites, consequently resulting in efficient reduction of the flammability parameters, such as heat release rate (HRR), total heat release (THR), smoke production rate (SPR), total smoke production (TSP), ignition time (IT) and so on. The morphological structures observed by SEM demonstrated that La2O3 could promote to form the homogenous and compact intumescent char layer. Thus, a suitable amount of La2O3 plays a synergistic effect in the flame retardancy and smoke suppression of IFR composites.