The improvement of CTA forward osmosis membrane performance by hydrophilic modification on interface between support layer and non-woven fabric

Abstract

Cellulose triacetate (CTA) forward osmosis (FO) membrane was fabricated with a polyvinyl alcohol (PVA)-modified nonwoven fabric (NWF) as a support material, which helps achieve a significant improvement in membrane performance. First, a surface modification was performed on the NWF by attaching PVA and glutaraldehyde to the fabric by cross-linking. Second, a CTA membrane was cast on the surface of the surface-modified NWF by phase inversion process. Then, the modified NWF and the modified CTA membrane were characterized by infrared spectroscopy, scanning electron microscopy (SEM), and the contact angle. It was found from the infrared spectroscopy that large quantities of hydroxyl group on the surface made the NWF more hydrophilic. It was also found from the SEM that, the PVA was not only attached on the surface of the fabric, but also embedded in the fabric. With the PVA content of the modified CTA membrane increased, the small sponge-like pores in the support layer were changed gradually into bigger finger-like pores. After the PVA modification, the contact angle of the NWF decreased from 116.9° to 38.5°, and that of the modified CTA membrane decreased from 114.1° to 55.8°, leading to a significant improvement in hydrophilicity. As a result, the water flux of the PVA-modified CTA FO membrane in FO mode was greatly improved up to 55 LMH. And the same time the Js/Jw was only 0.25. It has been calculated that the modified CTA membrane has a porosity of 0.51, and a tortuosity of 0.48, and a structural parameter of 93.65 μm. Compared the PVA-modified CTA membrane with several other FO membranes, it was found that the former has a smaller structural parameter and which can effectively reduce the internal concentration polarization in the support layer, thereby resulting in a significant improvement in membrane performance.