Mechanical and Transport Properties of Nanofiber Supported Thin Film Composite Membranes for Forward and Pressure Retarded Osmosis

Re-engineering the support layers of membranes for forward and pressure retarded osmosis is critical for making these technologies commercially viable.  Structural changes to the support layer must minimize internal concentration polarization without compromising its critical abilities to resist mechanical stress and provide a surface suitable for interfacial polymerization.  Electrospinning can provide nanofibers for support layers to potentially overcome the limitations of traditional membrane fabrication techniques in fulfilling these challenging design criteria.  In this work, we present the fabrication and evaluation of thin film composite membranes composed of electrospun poly(ethylene terephthalate) nanofibers, a phase separation formed microporous polysulfone layer, and a polyamide selective layer formed by interfacial polymerization.  These membranes have active and support layer transport properties that are suitable for engineered osmosis, with water permeability of 1.13 Lm^-2h^-1bar^-1, salt permeability of 0.232 Lm^-2h^-1, and a structural parameter of 651 μm.  Water flux in forward osmosis was 12.9 Lm^-2h^-1 with a deionized water feed solution and a 1 M NaCl draw solution.  Relevant and easily reproducible tests for mechanical resistance to stress were performed.  The use of electrospun fibers in the support layer enhanced membrane resistance to delamination at high cross flow velocities because the 340-nm diameter electrospun fibers enmesh with the microporous polysulfone layer.  Such resistance to delamination in membranes for engineered osmosis could not be achieved with fibers of the size produced by mechanical fiber fabrication techniques.  A broader discussion of the most promising approaches for using electrospun materials to improve membranes for engineered osmosis is provided.