Diffusion of CO2 Molecules in Polyethylene Terephthalate/Polylactide Blends Estimated by Molecular Dynamics Simulations

Molecular dynamics (MD) simulations have been used to study the diffusion behavior of small gas molecules (CO2) in polyethylene terephthalate (PET)/polylactide (PLA) blends. The Flory-Huggins interaction parameters (chi) determined from the cohesive energy densities are smaller than the critical value of Flory-Huggins interaction parameters (chi(critical)), and that indicates the good compatibility of PET/PLA blends. The diffusion coefficients of CO2 are determined via MD simulations at 298 K. That the order of diffusion coefficients is correlated with the availably fractional free volume (FFV) of CO2 in the PET/PLA blends means that the FFV plays a vital role in the diffusion behavior of CO2 molecules in PET/PLA blends. The slopes of the log (MSD) as a function of log (t) are close to unity over the entire composition range of PET/PLA blends, which confirmes the feasibility of MD approach reaches the normal diffusion regime of CO2 in PET/PLA blends.