Tortuosity model to predict the combined effects of crystallinity and nano-sized clay mineral on the water vapour barrier properties of polylactic acid

The combined effects of crystallinity and nano-sized clay mineral (montmorillonite) fillers on the water vapour barrier properties of poly(lactic acid) (PLA) nanocomposites are investigated. Both amorphous and semi-crystalline PLA nanocomposites containing 0 to 5 wt% montmorillonite clay are prepared by melt compounding followed by compression moulding with two different thermal treatments: quenching and annealing. Thermal properties and morphology are investigated using differential scanning calorimetry (DSC), polarised light microscopy, transmission electron microscopy (TEM) and wide-angle X-ray diffraction (WAXD). It is confirmed that the nanocomposite structures are intercalated and the montmorillonite aspect ratio is measured to be 40 in both quenched and annealed samples. Water vapour transmission rates (WVTR) through the film samples are measured. A new tortuous path model is developed that fits the WVTR data and accounts for the effects of crystallinity as well as montmorillonite aspect ratio, concentration and orientation.