Effect of supercritical CO2 pressure on polymer membranes

The aim of this study was to investigate the performance of polyamide membranes upon supercritical CO2 (SC-CO2) processing and depressurization. Membranes were processed up to 24 h at pressures of 120, 200 and 280 bar and their performance was investigated based on changes in physicochemical and morphological properties. These properties were studied by using contact angle, ATR-FTIR and FE-SEM. Two commercial polyamide membranes (AK and SG) were tested by measuring CO2 flux and oleic acid retention upon processing. Contact angle of AK exhibited a dramatic increase. ATR-FTIR results showed that absorbance of Nsingle bondH, Cdouble bond; length as m-dashO and Osingle bondH groups decreased with increasing pressure. While there was no obvious change in the morphology of SG membrane, bead-like structure formation was observed on AK membrane, which increased with pressure and/or processing time. Flux increased up to 54% with a 9% decrease in oleic acid retention for AK membrane after 24 h processing with SC-CO2 and depressurization. SG membrane was found to be more resistant upon depressurization due to its covalently cross linked structure. CO2 processing time and depressurization were found to be very effective in reorganization of the polymer network, especially when high level of hydrogen bonding is involved in its structure, which would limit the use of membranes for further processing.