Supercritical CO2 permeation in polymeric films: Design, characterization, and modeling

This study is concerned with the development of an optimum method for identification of supercritical CO2 permeability in thermoplastic films with moderate to excellent barrier properties namely, High-Density Polyethylene (HDPE), Raised-Temperature Polyethylene (PE-RT), Polyvinylidene Fluoride (PVDF) and aliphatic Polyketone (PK) at elevated temperatures (40 °C−82 °C). A high-temperature/high-pressure permeation cell was designed based on the “closed-volume/variable pressure” standard test method. The identified gas transport properties using the time lag method yielded significant error particularly for PVDF and PK, which was ascribed to the sole reliance on the accumulated pressure-rate in steady-state. This error was minimized using the Non-Linear Regression (NLR) by utilizing the full range of measured data including the transient state. The coefficient of determination between the measured and modeled data using NLR was quantified above 0.99 for all the polymers at the entire examined temperature range. The 1.4 % higher degree of crystallinity and 28.5 % smaller spherulite size caused 13.3 % higher diffusivity and 8.6 % lower solubility in PE-RT when compared with HDPE at 82°C. As a result of this trade-off, PE-RT exhibited only 3.5 % higher permeability than HDPE. The developed generalized temperature-dependent model provided the essential data for design optimization of gas barrier performance in multilayer high-temperature pressure-vessels.