Polymer Nanocomposites Using Zinc Aluminum and Magnesium Aluminum Oleate Layered Double Hydroxides: Effects of LDH Divalent Metals on Dispersion, Thermal, Mechanical and Fire Performance in Various Polymers
Oleate-containing layered double hydroxides of zinc aluminum (ZnAl) and magnesium aluminum (MgAl) were used to prepare nanocomposites of polyethylene, poly(ethylene-co-butyl acrylate) and poly(methyl methacrylate). The additives and/or their polymer composites were characterized by X-ray diffraction, FTIR, elemental analysis, thermogravimetric analysis, mechanical testing, and cone calorimetry. The unusual packing of the monounsaturated oleate anions in the gallery of these LDHs facilitates the dispersion of these nanomaterials. The inorganic LDH protects the polymer from thermal oxidation, shown by enhancement of the thermal and fire properties of the corresponding polymer nanocomposites. There is a qualitative difference in the morphology of the two LDHs in PE and PMMA. ZnAl is better dispersed in PE while MgAl is better dispersed in PMMA. The zinc-containing material led to a large reduction in the peak heat release rate in polyethylene, while the magnesium-containing material led to enhancement of the fire properties of the more polar poly(methyl methacrylate). These fire properties are consistent with the morphological differences. Neither of these LDHs shows efficacy with poly(ethylene-co-butyl acrylate), which indicates a selective interaction between the LDH and the various polymers.