Impact of Soft Segment Size on Structural and Permeation Properties of Polyurethane Membranes

A series of polyurethane membranes were synthesized through poly-addition polymerization for reverse osmosis application. Poly (ethylene glycol) with different molecular weights was used as a soft segment and structural and performance properties of membranes were investigated. FTIR spectra of membranes verified the presence of incorporated monomers and the development of urethane linkages. The water content and surface roughness of the membranes were increased progressively with an increase in the size of the soft segment. The surface hydrophilicity and development of porous structure of membranes increased water flux with compromised salt rejection as size of the soft segment was increased. The permeation properties of the membranes including salt rejection and water flux were recorded by a dead-end reverse osmosis unit. PU-3PEG membrane showed the highest salt rejection (88%) whereas the PU-15PEG membrane exhibited the highest water flux (20.7 L/h m²) at effective pressure of 60 bar. The gel content of PU membranes was decreased with increase in the molecular weight of soft segment (PEG). The antibacterial property of PU membranes was validated by the successful inhibition of the gram negative bacterium “Escherichia coli”. These results proved to be influential in interpreting the structure–property relationship of polyurethane membranes for RO process.