Robust surface modified polyetherimide hollow fiber membrane for long-term desalination by membrane distillation

Surface modified polyetherimide (PEI)hollow fibers were prepared by surface segregation of a fluorinated polyurethane additive (FPA). This undergoes spontaneous segregation principally to their outer surfaces resulting in PEI hollow fibers with an improved hydrophobic property of a contact angle up to 132.7°. This high contact angle is attributed mainly to the protrusion of fluorine of FPA at the hollow fiber surface. The addition of FPA also enhanced the mechanical strength and liquid entry pressure of water (LEP)reaching high values in the range 329–541 kPa. The effects of the PEI concentration in the blend on the morphological and structural characteristics of the hollow fibers were studied maintaining the FPA at 2 wt% in the PEI spinning solution. The hollow fibers were tested for desalination by direct contact membrane distillation (DCMD). A very stable DCMD performance was obtained for the FPA hollow fiber prepared with 14 wt% PEI with permeate fluxes around 23.8 kg/m² h and low permeate electrical conductivity (4.9–5.8 μS/cm)over a period of almost two months (54 days DCMD operation with 29.8 g/L NaCl aqueous solution, 80 °C and 20 °C feed and permeate inlet temperatures, respectively).