Abstract: Expandable graphite (EG) and traditional intumescent flame retardant (IFR) were introduced into polyethylene (PE). The flame retardant properties of the system was studied using differential scanning calorimetery (DSC), Fourier transform infrared spectroscopy (FTIR) and testing of limited oxygen index. A strong synergistic effect between EG and IFR was observed. As a result, a limited oxygen index value of 31.5 % was achieved by adding 30 phr EG/IFR in PE, which was much higher than that of PE/EG or PE/IFR. The physical interaction between EG and IFR during thermal degradation was proved by their individual degradation behavior and char structure of the composite. The char formed by thermal degradation of EG and IFR was integrated to form an efficient barrier to oxygen and heat, which were in favor of the flame retardant properties.

Key words: polyethylene, intumescent flame retardant, expandable graphite, synergistic effect, limited oxygen index