Structure and Transport Properties of Mixed-Matrix Membranes Based on Polyimides with ZrO₂ Nanostars.

Mixed-matrix membranes based on amorphous and semi-crystalline polyimides with zirconium dioxide (ZrO₂) nanostars were synthesized. Amorphous poly(4,4'-oxydiphenylenepyromellitimide) and semi-crystalline polyimide prepared from 1,4-bis(4-aminophenoxy)benzene and 4,4'-oxydiphthalic anhydride were used. The effect of ZrO₂ nanostars on the structure and morphology of nanocomposite membranes was studied by wide-angle X-ray scattering, scanning electron microscopy, atomic force microscopy, and contact angle measurements. Thermal properties and stability were investigated by thermogravimetric analysis and differential scanning calorimetry. Transport properties of hybrid membranes containing 5 wt % ZrO₂ were tested for pervaporation of a mixture of butanol⁻water with 10 wt % H₂O content. It was found that a significant amount of the ZrO₂ added to the semi-crystalline polyimide is encapsulated inside spherulites. Therefore, the beneficial influence of inorganic filler on the selectivity of mixed-matrix membrane with respect to water was hampered. Mixed-matrix membranes based on amorphous polymer demonstrated the best performance, because water molecules had higher access to inorganic particles.