Fine dispersion of phosphazene-amines and silicate platelets in epoxy nanocomposites and the synergistic fire-retarding effect

摘要

We have synthesized the phosphazene-amine adduct of hexachlorocyclophosphazene (HCP) and poly(oxypropylene)-diamines of 400 g/mol molecular weight (D400) by amine/chloride substitution and HCl removal by triethylamine. Subsequently, the adduct HCP-D400 was physically mixed with exfoliated silicate platelets (SP) to prepare the HCP-D400/silicate hybrids (HCP-D400/SP). This preparation was performed at low temperature for homogeneous mixing due to the lower critical aggregation temperature (LCAT) character of HCP-D400. The HCP-D400/SP hybrids of three different weight compositions were evaluated for thermal decomposition and fire retarding properties in further mixing with an epoxy to form polymer composites. We have also prepared the HCP-D400/MMT hybrid by intercalating the layered sodium montmorillonite (Na~+ -MMT) with HCP-D400; and the controlled hybrid (HCP-D400/Na~+ -MMT) by the physical mixing of HCP-D400 with Na~+ -MMT. The analyses by SEM-EDX, XRD, and TEM indicated that the HCP-D400/SP/epoxy composites had a more homogeneous silicate distribution in the polymer matrix than the HCP-D400/MMT and HCP-D400/Na~+ -MMT counterparts. The thermal gravimetric analysis (TGA) revealed that the epoxy composite with 10 wt.% of HCP-D400/SP, HCP-D400/MMT, and HCP-D400 had a degradation temperature of 757, 712, and 519 °C at 80 % weight loss, respectively, in comparison with the 500 °C of the pristine epoxy system. Anti-flame test confirmed that the HCP-D400/SP/epoxy had a higher limit oxygen index (LOI) of 27 % than the HCP-D400/MMT counterpart (24 %). The degree of exfoliating the layered clay into random silicate platelets is the predominant factor for the thermal stability enhancement. It is also demonstrated that the copresence of phosphazene-amines and silicate platelets has a synergistic effect in improving the thermal behavior of the epoxy composites.