New nanocomposites have been prepared using unmodified polypropylene (PP) and a new form of highly-dispersed AMOZn2Al-borate and AMO-Mg3Al-borate layered double hydroxides (LDHs), with various LDH loadings of 1, 3, 6, 9, 15 and 30 wt%. Scanning electron microscopy (SEM) analysis shows that these nanocomposites form spherical particles with an average size of ca. 10 μm and that the LDH nanoparticles were well dispersed within the PP matrix. XRD analysis of the nanocomposites indicates that the LDHs are completely exfoliated. The thermal stability and flame retardancy properties of these new materials have been evaluated as a function of the nature of LDH and the LDH loadings (wt%). Cone calorimetry analysis indicated that PP/Zn2Al-borate nanocomposites exhibited superior performance than the equivalent PP/Mg3Al-borate nanocomposites; a 15 wt% of the highly dispersed Zn2Al-borate LDH in polypropylene was found to be the optimal loading. For this composition the peak heat release rate (PHRR) = 614 kW/m2, total heat release (THR) = 95.4 MJ/m2, average mass loss rate (10 to 90%) AMLR = 12.7 g/m2s with a final char of 9.5 %. Equivalent measurements on pristine polypropylene gave PHRR = 1693.0 kW/m2, THR = 198.5 MJ/m2, AMLR = 28.2 g/m2s with a final char of 0%. The 15% Zn2Al-borate LDH in pristine (unmodified) PP resulted in reduction of the PHRR (Rdctn) by 63.7%.
