Iron-containing, high aspect ratio clay as nanoarmor that imparts substantial thermal/flame protection to polyurethane with a single electrostatically-deposited bilayer

Abstract

In an effort to impart fire protection properties to polyurethane foam using environmentally-benign components, layer-by-layer assembly is used to fabricate nanobrick wall thin films of branched polyethylenimine (PEI), chitosan (CH), and sodium montmorillonite (MMT) (or formulated vermiculite (VMT)) clay bricks. Using specially formulated, large-aspect-ratio VMT platelets, a single polymer/clay bilayer deposited on polyurethane foam (3.2 wt% addition) was able to cut the peak heat release rate in half, reduce smoke release, and eliminate melt dripping. It takes 4 polymer/MMT bilayers to match these flame retardant properties and weight gain, indicating that nanoplatelet aspect ratio significantly enhances the nanocoating's ability to reduce heat transfer and prevent mass loss. This study demonstrates a simple, commercially viable, and effective fire protection alternative. Desirable fire performance properties for polyurethane foam no longer have to come at the cost of laborious, multi-step coating procedures or in choosing halogenated additives that are currently being scrutinized due to their potentially adverse effects to human health.