Effects of sulfonation degree on compatibility and separation performance of polybenzimidazole (PBI)-sulfonated polyphenylenesulfone (sPPSU) blend membranes

The molecular compatibility between polybenzimidazole (PBI) and sulfonated polyphenylsulfone (sPPSU) and their blend membranes for herbicide removal in water reuse and for drug separation in organic solvent nanofiltration (OSN) have been investigated as a function of sulfonation degree in sPPSU. Flat sheet membranes cast from PBI-sPPSU blends with a mass ratio of 1:1 were prepared and then crosslinked by trimesoyl chloride (TMC) at room temperature. The blend made of PBI and 12.7 mol% sPPSU showed high compatibility based on the calculated enthalpy of mixing (ΔHm), measured dope viscosity, phase diagram, and single Tg. The TMC modified membrane cast from this composition also exhibited higher chemical resistance, mechanical stability, narrower pore size and pore size distribution, macrovoid-free structure and better separation performance. All fabricated membranes were evaluated using feeds containing tetracycline (MW = 444 Da) as a model drug in ethanol and pendimethalin (MW = 281.3 Da) as a model herbicide in water. The crosslinked PBI-12.7 mol% sPPSU (12.7C) membrane exhibited rejection of >96% against low-molecular-weight pendimethalin from water and tetracycline from ethanol. It also has the capability to separate mixed solutes, even with small molecular weights. This study illustrates the effectiveness of highly compatible polymer blends with the aid of one-step cross-linking modification for nanofiltration.