Flame retardancy of polymers

Thin films prepared via 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 (3 and 6), was paired with anionic montmorillonite (MMT) clay nanoplatelets. Thin film assemblies prepared with CH at high pH are thicker due to 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.