Enhancement of Water Vapor Barrier Properties of Biodegradable Poly(butylene adipate-co-terephthalate) Films with Highly Oriented Organomontmorillonite

Low water vapor permeability is highly demanded for biodegradable packaging and agricultural film applications. However, biodegradable poly(butylene adipate-co-terephthalate) (PBAT) films demonstrate poor water vapor barrier properties. A series of nanocomposite (NC) films composed of organically modified montmorillonite (OMMT) dispersed at levels ranging from 0 to 13 wt % in PBAT were thus generated using both film blowing and biaxial orientation. Films were characterized with wide-angle X-ray diffraction, transmission electron microscopy, thermal analysis and mechanical testing (static and dynamic), and their water vapor permeation (WVP) values were determined. The WVP of PBAT-OMMT NC films relative to that of the pure PBAT dropped and began leveling at the maximum OMMT concentrations tested. NCs for which OMMT layers better aligned with film surfaces, in this case those generated via biaxial orientation, provided for faster and more substantial decreases in WVP values relative to those produced with film blowing. The WVPs can be predicted using the Bharadwaj model, which accounts for OMMT aspect ratio, concentration, as well as orientation. The experimental results are in good agreement with the prediction values of the model. The addition of 13 wt % OMMT more than doubled the Young's modulus, but resulting in a decrease of film tensile strength. The elongation at break was found to initially climb up to OMMT levels of about 6 wt % but declines sharply with higher concentrations. Results demonstrate the viability of reducing WVP levels of PBAT using orientated OMMT addition and provide insights on key structural parameters.