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.

No abstract

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.

Single bilayer polymer/clay nanobrick wall self-assembled thin films, deposited as a continuous coating on open-celled polyurethane foam, cut peak heat release rate in half with only 3.2 wt% addition.