Novel charged and hydrophilized polybenzimidazole (PBI) membranes for forward osmosis

Polybenzimidazole (PBI) is a material with excellent chemical resistance, and thermal and mechanical stabilities. However, significant drawbacks of PBI that prevent its use as a membrane for water purification applications include hydrophobicity and neutral surface charge at neutral pH values. Surface functionalization was investigated as a means to circumvent these drawbacks by modifying PBI membranes to increase hydrophilicity and surface charge. The modifying agents used for functionalization included: p-phenylene diamine, ethylene diamine, taurine, and poly(acrylamide-co-acrylic acid). Functionalized asymmetric flat sheet PBI membranes were investigated in forward osmosis (FO) applications. The FO process involved semi-permeable flat sheet membranes with an ammonium bicarbonate draw solution and a sodium chloride feed solution. The functionalized membrane surfaces exhibit increased hydrophilicity, surface charge, and reduced pore sizes. Additionally, all membrane modifications show increased water flux and a reduction in sodium chloride transport.