Effects of functional intercalation and surface modification on the flame retardant performance of EVA/LDHs composites

Mg/Al/Fe ternary layered double hydroxides (LDHs) were synthesized by a coprecipitation method using activated Bayer red mud as raw materials. Then, the prepared LDHs were intercalated with sodium dodecyl sulfate (SDS) and modified with (3-aminopropyl)triethoxysilane (KH550) at the surface. All samples were characterized by X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, Fourier transform infrared spectrometry, and contact angle measurement. As flame-retardant filler, the KH550-modified composites showed better compatibility in comparison with both the original LDH and LDH-SDS. The composite ELDH-SDS-KH (ethylene-vinyl acetate/LDHs composites) showed not only a significant reduction in heat release rate, smoke production rate, and total heat release during combustion, but high thermal stability and less production of aliphatic hydrocarbons and carboxylic acid were also observed in comparison with other composites. Moreover, when the added amount of LDH is 50 wt%, the tensile strength value of ELDH-SDS-KH was 9.8 MPa, and the elongation at break value was 427%, which is significantly improved compared with ELDH (with the tensile strength value of 6.3 MPa and the elongation at break value 38%).