Polymer nanocomposites using zinc aluminum and magnesium aluminum oleate layered double hydroxides: Effects of the polymeric compatibilizer and of composition on the thermal and fire properties of PP/LDH nanocomposites

A series of five oleate-containing layered double hydroxides with varied ratios of zinc to magnesium, i.e., with the general formula Zn_2-yMg_yAl(OH)₆ [CH₃(CH₂)₇CH{double bond, long}CH(CH₂)₇COO]·nH₂O, were synthesized and used to prepare nanocomposites of polypropylene (PP). The nanomaterials were characterized by elemental analysis, attenuated total reflection-infrared spectroscopy (ATR-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA), while the composites were characterized by XRD, TGA, transmission electron microscopy (TEM) and cone calorimetry. The zinc-containing LDH showed better dispersion in the polymer at the micrometer level than did the magnesium-containing LDH while both are equally well-dispersed at the nanometer level. The magnesium-containing composites led to more thermally stable systems in TGA experiments, while the zinc systems gave greater reductions in heat release rate during combustion. Dispersion was also affected by the amount of PP-g-MA which was present. More PP-g-MA gave better dispersion and a significantly reduced peak heat release rate, i.e., enhanced fire performance.