A comparative study on the synergistic effect of expandable graphite with APP and IFR in polyethylene

In this study, synergistic effects of expandable graphite (EG) and ammonium polyphosphate (APP) or intumescent flame retardant (IFR) on flame retardant polyethylene (PE) have been comparatively investigated by means of limiting oxygen index (LOI), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). The results of LOI reveal better synergistic effects of EG with IFR than that with APP. According to TGA and SEM results, EG/APP can retard the degradation to some extent, while EG/IFR can promote the formation of a more compact char layer, consequently leading to much lower weight loss rate and better flame retardant synergistic effect of EG with IFR. EDS gives positive evidences of the interaction of EG/APP or EG/IFR by showing the char that is rich in elements P and S.