Coupling silsesquioxane nanocages into Fe-Mg-Al layered metal hydroxide for enhanced flame retardancy and surface charring of silicone elastomer

Abstract

Bonding of two-dimensional layered metal hydroxides (LMHs) to silicone rubber (SR) is not yet common, mainly due to the hydrophilic surface and limited layer spacing of LMHs, which make it difficult to achieve uniform distribution. In this work, we modified Fe-Mg-Al LMH nanoparticles by incorporating silsesquioxane nanocages bearing anionic benzoate groups and polyethylene glycol chains (SQ–COOH) using a co-precipitation procedure. The modification step leads to an enlarged interlayer spacing for LMHs and simultaneously transforms their intrinsic hydrophilic surfaces into hydrophobic ones, originating from the rigid and bulky nature and also the intercalation capacity of the modifiers. When melt-blended with SR, this SQ–COOH-incorporating strategy allowed an enhanced LMH dispersion via an interfacial compatibilization between the elastomer matrix and the modified nanoparticles. The resulting SR/LMH@SQ–COOH composites showed the expected improvement in mechanical properties while demonstrating outstanding thermal stability and flame retardancy performance. Most importantly, the synergistic effect of Fe-Mg-Al LMH with SQ–COOH endows this SR composite with significant surface charring ability resulting in a compact and strengthened ceramic-like layer to inhibit progressive combustion, which will find application in packing and other utility.