Enhanced Matrimid membranes for pervaporation by homogenous blends with polybenzimidazole (PBI)

We have demonstrated that the incorporation of a small amount of polybenzimidazole (PBI) into Matrimid polyimide can significantly stabilize Matrimid's polymeric chains for high-temperature pervaporation and remarkably enhance the separation factor/selectivity and flux/permeance for the dehydration of tert-butanol/water mixtures. The strong interactions between the carbonyl group of Matrimid and the NH group of PBI are the cause for the enhanced chain stability, while the hydrophilic nature of PBI and the close chain packing may be the reasons for the high separation performance. Data from DSC, TMA, DMA and FTIR confirm that the PBI/Matrimid blends studied are miscible in molecular level, but the degree of miscibility apparently decreases with an increase in PBI. It is found that annealing plays an important role on membrane structure and separation performance. Not only can it induce chains rearrangement towards a dense packing and the formation of charge transfer complexes (CTC), but also significantly improve separation factor and selectivity. Pervaporation experiments conducted at room and elevated temperatures all indicate that the blend membrane with 3.55 wt.% PBI has the best separation performance, which is consistent with the smallest d-space value measured by XRD. In addition, both DMA and pervaporation experiments verify that the blending of a small amount of PBI with Matrimid can efficiently overcome the plasticization of Matrimid at high temperature operation.