Amanda A. Cain

Clay–Chitosan Nanobrick Walls: Completely Renewable Gas Barrier and Flame-Retardant Nanocoatings

Thin films prepared via a layer-by-layer (LbL) assembly of renewable materials exhibit exceptional oxygen barrier and flame-retardant properties. Positively charged chitosan (CH), at two different pH levels (pH 3 and pH 6), was paired with anionic montmorillonite (MMT) clay nanoplatelets. Thin-film assemblies prepared with CH at high pH are thicker, because if the low polymer charge density. A 30-bilayer (CH pH 6-MMT) nanocoating (~100 nm thick) reduces the oxygen permeability of a 0.5-mm-thick polylactic acid film by four orders of magnitude. This same coating system completely stops the melting of a flexible polyurethane foam, when exposed to direct flame from a butane torch, with just 10 bilayers (~30 nm thick). Cone calorimetry confirms that this coated foam exhibited a reduced peak heat-release rate, by as much as 52%, relative to the uncoated control. These environmentally benign nanocoatings could prove beneficial for new types of food packaging or a replacement for environmentally persistent antiflammable compounds.

Inorganic Nanoparticle Thin Film that Suppresses Flammability of Polyurethane with only a Single Electrostatically-Assembled Bilayer

In an effort to reduce the flammability of polyurethane foam, a thin film of renewable inorganic nanoparticles (i.e., anionic vermiculite [VMT] and cationic boehmite [BMT]) was deposited on polyurethane foam via layer-by-layer (LbL) assembly. One, two, and three bilayers (BL) of BMT-VMT resulted in foam with retained shape after being exposed to a butane flame for 10 s, while uncoated foam was completely consumed. Cone calorimetry confirmed that the coated foam exhibited a 55% reduction in peak heat release rate with only a single bilayer deposited. Moreover, this protective nanocoating reduced total smoke release by 50% relative to untreated foam. This study revealed that 1 BL, adding just 4.5 wt % to PU foam, is an effective and conformal flame retardant coating. These results demonstrate one of the most efficient and renewable nanocoatings prepared using LbL assembly, taking this technology another step closer to commercial viability.

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

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 nanocoatings 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.