Synergistic effect of lanthanum oxide on the flame retardant properties and mechanism of an intumescent flame retardant PLA composites

Abstract

The synergistic effect of lanthanum oxide (La2O3) on the flame retardant properties and mechanism of a novel intumescent flame retardant polylactide composites (PLA/IFR) was investigated by the means of limited oxygen index (LOI), catalytic effectivity analysis (CAT-EFF), vertical burning test (UL-94), microscale combustion calorimetry (MCC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), Laser Raman spectroscopy (LRS) and X-ray photoelectron spectroscopy (XPS). La2O3 enhanced the LOI value of the PLA/IFR composite dramatically and all the composites passed the UL-94 V-0 rating test. PLA/IFR/1% La2O3 had the highest CAT-EFF, and the LOI value of the composite increased from 32.8 to 42.2% according to catalytic affectivity (CAT-EFF) analysis. 1%La2O3 enhanced the fire retardant performance of PLA/IFR, resulting consequently in reduction of heat release rate (HRR), total heat release (THR), heat release capacity (HRC) and degree of flammability (Findex) of the PLA/IFR. The TGA test revealed that La2O3 changed the degradation behavior of the PLA/IFR, enhanced the thermal stability of the PLA/IFR at high temperature and increased the char residue. The morphological structures observed by SEM demonstrated that La2O3 effectively help to form more continuous and compact intumescent char layer on the surface. The LRS results indicated that higher graphitization degree of the residue char was formed. The EDS and XPS results illustrated that the existence of La2O3 promoted to remain more P and O in the char layer to form more crosslinking structure to improve barrier properties of the char layer.