On O2 gas permeability of PP/PLA/clay nanocomposites: A molecular dynamic simulation approach

Polypropylene/poly(lactic acid) (PP/PLA) blends were prepared by reactive blending in a co-rotating twin-screw extruder. Effect of blend composition on oxygen permeability through compression molded films was investigated and correlated to the microstructure. Two blends, PP-rich (75/25) and PLA-rich (25/75), were selected in order to consider the effect of incorporation of clay and compatibilization on the permeability. The PP-rich blends had greater oxygen barrier properties compared to those of PLA-rich blends. Several proposed models of permeability for blends and nanocomposites were examined. These models failed to predict the permeability values, especially for PLA-rich blends. The failure was attributed to the immiscibility issue leading to appearance of microvoids at the interface. Molecular dynamics simulations were performed by employing the COMPASS force field to estimate the diffusivity of oxygen gas through pure components, PP-rich and PLA-rich systems. The simulated results were in good agreement with the available experimental data.