Synthesis and characterization of LDHs using Bayer red mud and its flame-retardant properties in EVA/LDHs composites

Red mud is one of the largest industrial solid wastes in the aluminum industry, which has caused serious environmental and safety issues. In this paper, it is to explore a new technology of synthesizing layered double hydroxides (LDHs) using red mud for flame-retardant ethylene-vinyl acetate (EVA). A series of ternary layered double hydroxides (LDHs: Mg/Al/Fe-LDHs, Ni/Al/Fe-LDHs, Cu/Al/Fe-LDHs and Zn/Al/Fe-LDHs) were prepared using Bayer red mud (BRM) as raw materials by a calcinations-rehydration method. The structures of LDHs were characterized using X-ray diffraction (XRD). The XRD results indicated that LDHs were successfully synthesized; and the structures of Mg/Al/Fe-LDHs were better than the other ones. The SEM analysis results showed that Mg/Al/Fe-LDHs had better dispersity than that of BRM. Then, the flame-retardant properties of Mg/Al/Fe-LDHs in EVA/LDHs composites had been studied by cone calorimeter test (CCT) and limiting oxygen index (LOI). The CCT results showed that the heat release rate (HRR) of EVA/Mg/Al/Fe-LDHs obviously decreased in comparison with that of EVA/BRM composite and the PHRR value of ELDH4 sample was the lowest among all samples. The LOI results showed that ELDH4 has the highest LOI value. In this paper, the method for synthesis of LDHs based on BRM has low cost and feasible technology, which is expected to achieve good economic and environmental benefits.