Abstract
The suppression of CO 2 -induced plasticization in polyimide membranes at supercritical conditions up to 120 bar is investigated. Three approaches (polymer blending, thermal treatments and chemical crosslinking) known from relatively low-pressure applications are applied and their effectiveness to suppress membrane plasticization at high CO 2 pressures and under supercritical conditions is systematically identified. CO 2 sorption measurements reveal that especially Henry sorption promotes plasticization and that the corresponding Henry sorption parameter (k D ) correlates with the d-spacing and T g of the membranes. A lower d-spacing and higher T g results in a reduced k D parameter and thus a higher resistance to plasticization. A high interchain rigidity is required to suppress plasticization at the highly plasticizing liquid-like CO 2 densities. Chemical and thermo-oxidative crosslinking results in the largest decrease in interchain mobility and therefore shows the highest resistance to plasticization, but also a significantly lower permeability. Thermally treating the membranes in N 2 retains a high permeability, while still displaying significant plasticization resistance. Polymer blending does increase the plasticization resistance, but strongly reduces the permeability. All three methods manage to suppress plasticization at supercritical conditions, but crosslinking offers superior plasticization resistance. However, proper tailoring strategies are required to combine a high plasticization resistance with a high permeability. • Evaluation of methods to suppress CO 2 -plasticization at supercritical conditions. • D-spacing and chain mobility are essential parameters to suppress plasticization. • Henry sorption parameter (k D ) correlates with d-spacing and T g . • Formation of CTC’s during thermal treatments promotes resistance to plasticization. • Chemical and thermal crosslinking offers superior resistance to plasticization.
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