Oxygen barrier of multilayer thin films comprised of polysaccharides and clay

Multilayered thin films of chitosan (CH), carrageenan (CR) and montmorillonite (MMT) clay, deposited using the layer-by-layer technique, were studied in an effort to produce fully renewable polysaccharide-based thin films with low oxygen permeability. Ten ‘trilayers’ of CH/MMT/CR (<40 nm thick) on PET film reduced its oxygen permeability (1.76 × 10⁻¹⁵ cm³ cm/cm² s Pa) by an order of magnitude under dry conditions. By adding an additional layer of CH to the trilayer sequence, a ‘quadlayer’ film of CH/CR/CH/MMT (<60 nm thick) was created, which was able to reduce oxygen permeability of PET by two orders of magnitude under the same conditions. This high oxygen barrier is believed to be due to the unique nanostructure of these films, often referred to as a “nanobrick wall” structure, as well as a strong association amongst the oppositely charged polysaccharides. Combining fully renewable and food contact approved ingredients with high gas barrier and optical transparency makes this technology promising as a foil replacement for food packaging.