Pure and mixed fluid sorption and transport in Celazole® polybenzimidazole: Effect of plasticization

Tough polymers are recognized as ideal membrane materials for gas and liquid separations in harsh environments. However, while solvent flux and solute rejection data, as well as permeability and selectivity data for light gases are widely available in the literature, fundamental studies of organic species transport in tough polymers and their correlation with the membrane structure are rare. This study focuses on the solubility of pure and mixed organic species in Celazole®, a commercial polybenzimidazole. Methanol was selected as a model penetrant to run sorption and diffusion experiments in the activity range 0–1. The role of polymer-penetrant interactions, membrane degree of swelling, and penetrant clustering on small molecule sorption and transport in Celazole® was discussed and several structure-property correlations were identified. Remarkably, polar penetrants, such as methanol, cause severe matrix plasticization. In contrast, Celazole® is highly stable in non-polar aliphatic and aromatic hydrocarbons. Finally, the polymer mechanical properties were measured before and after soaking in liquid water and methanol.