Thermal Analysis and Flame-Retarded Mechanism of Composites Composed of Ethylene Vinyl Acetate and Layered Double Hydroxides Containing Transition Metals (Mn, Co, Cu, Zn)

The effects of transition metals on the hydrophobicity of nano-structured layered double hydroxides (LDHs) and the compatibility of LDHs/ethylene vinyl acetate (EVA) composites have seldom been reported. NiMgAl-LDHs slightly surface-modified with stearate and doped with transition metal cations (Mn2+, Co2+, Cu2+, Zn2+) are investigated. Compared to the pure EVA, not only were the maximal degradation-rate temperatures (T-max) of the ethylene-based chains enhanced, but also the smoke production rate (SPR) and the production rate of CO (COP) were sharply decreased for all the composites. Most importantly, a new flame retardant mechanism was found, namely the peak heat release rate (pk-HRR) time, which directly depends on the peak production rate of CO2 (pk-CO2) time for EVA and all composites by cone calorimeter test. Moreover, the Mn-doped LDH S-NiMgAl-Mn shows more uniform dispersion and better interfacial compatibility in the EVA matrix. The cone calorimetric residue of S-NiMgAl-Mn/EVA has the intumescent char layer and the compact metal oxide layer. Therefore, S-NiMgAl-Mn/EVA shows the lowest pk-HRR and the longest pk-HRR time among all the composites.