Theoretical and experimental investigation of selective gas permeability in polystyrene/polyolefin elastomer/nanoclay nanocomposite films

Nanoclay (NC) has gas barrier properties that, when used in food packaging, protects food against spoilage. Moreover, food packaging frequently makes use of rigid and foamed polystyrene (PS). In this work, reactive blending in a co-rotating twin-screw extruder was used to process PS, polyolefin elastomer (POE), and NC blends, leading to microphase-separated PS/POE/NC nanocomposite films. The structural and CO2 and N2 barrier properties of the resulting films were determined. The distribution of the NC platelets in the blends was theoretically predicted using the wetting coefficients. Nearly all NC platelets were found in the PS phase, in agreement with the theoretical predictions. Moreover, the NC platelets were found to be concentrated at the interfacial zones between the polymer phases when a compatibilizer was added to the blend. Scanning electron microscopy, wide-angle X-ray scattering, and transmission electron microscopy were used to examine the microstructure of the PS/POE/NC nanocomposites. Adding NCs as a gas barrier component to the PS/POE blend resulted in a decrease in CO2 and N2 permeability. For a better understanding of the gas diffusion in the pure PS and POE, as well as PS/POE blend, molecular dynamics simulations were performed to enable the calculation of gas diffusion coefficients in the different systems. The simulation results confirmed the experimental trends observed in this work.