Structure control of asymmetric poly(vinyl butyral)‐TiO 2 composite membrane prepared by nonsolvent induced phase separation

Poly(vinyl butyral) (PVB)‐TiO 2 composite hollow fiber membranes were prepared via nonsolvent induced phase separation (NIPS). The membrane had a skin layer on both the outer and inner surface at the initial stage after membrane preparation. However, the outer surface became porous with the passage of time, as the polymer in the membrane's outer surface was decomposed by the photocatalysis of TiO 2 . The initial water permeability increased with the increase of TiO 2 content. Furthermore, for all the membranes, as time elapsed the water permeabilities increased and became constant after about 15 days, which was in accordance with the alteration on the membrane's outer surface. Despite decomposition of the polymer on the outer surface, particle rejection hardly changed because the inner surface kept the original structure. Thus, addition of TiO 2 to the membrane is a useful way to improve water permeability while maintaining particle rejection. The clear asymmetric structure with both porous structure at the outer surface and skin layer at the inner surface was achieved by the addition of TiO 2 . Therefore, the addition of TiO 2 is a new method for achieving the high porosity at the outer surface of the hollow fiber membrane. In addition, tensile strength and elasticity kept constant over time and were higher than those of original PVB membranes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008