An Experimental and Theoretical Investigation on the Diffusion of Olefins in Semi-Crystalline Polymers: The Influence of Swelling in Polymer-Penetrant Systems

摘要

A comprehensive dynamic diffusion model has been developed to predict the diffusion coefficient of low molecular weight penetrants in semi-crystalline polymer films. The model takes into account the extent of polymer swelling on penetrant diffusion flux, resulting in a moving boundary value problem. The free volume theory is employed to calculate the dependence of the diffusion coefficient on the penetrant concentration. The diffusivities of ethylene and propylene in semi-crystalline polyethylene films at elevated pressures and temperatures are measured by carrying out sorption experiments using a Ru-botherm~® magnetic suspension microbalance. In addition, the extent of polymer swelling is measured by monitoring the volume change of the polymer film via an optical apparatus, operated in series with the suspension microbalance. The theoretical predictions of the proposed model are found in excellent agreement with the experimental measurements. It is shown that the value of the penetrant diffusion coefficient significantly varies during the sorption process.