(614e) Clay-Chitosan Nanobrick Walls: Renewable Multilayer Thin Films for Foil Replacement and Flame Suppression

Multilayered thin films assembled with “green” food contact approved materials (i.e., chitosan (CH) and montmorillonite (MMT) clay) were deposited on polylactic acid (PLA) films.  PLA has poor oxygen barrier properties relative to petroleum-based polymers that are widely used as food packaging (e.g. polyethylene terephthalate (PET)). A thirty bilayer CH-MMT assembly (~100 nm thick) on PLA exhibits an oxygen transmission rate (OTR) below the detection limit of commercial instrumentation (≤0.005 cm³/(m²·day·atm)). This high barrier behavior is believed to be due to the brick wall nanostructure that produces an extremely tortuous path for oxygen molecules to take as they permeate through the film. Ten bilayers (~30 nm thick) of this same recipe was deposited on flexible polyurethane foam, in an effort to create an environmentally-friendly flame retardant system. This coating completely stopped foam melting after exposure to direct flame from a butane torch. When cut open, undamaged white flexible foam was revealed under a relatively thin (~ 2 mm) black char layer. Cone calorimetry reveals a peak heat release rate reduced by 52% relative to the uncoated control. These environmentally benign nanocoatings could act as a replacement for packaging foil or toxic antiflammable compounds.