A morphological study of ceramic hollow fibre membranes

Morphologies of ceramic hollow fibre membranes prepared from suspensions of Al2O3, NMP (N-methyl-2-pyrrolidone) and polyethersulfone (PESf) using a dry–wet spinning/sintering process have been studied experimentally. The results indicate that two types of membrane morphologies, i.e. finger-like and sponge-like structures can be expected. It is believed that finger-like void formation in asymmetric ceramic membranes is initiated by hydrodynamically unstable viscous fingering developed when a less viscous fluid (non-solvent) is in contact with a higher viscosity fluid (ceramic suspension containing invertible polymer binder). Finger-like void growth occurs only below a critical suspension viscosity, above which a sponge-like structure is observed over the entire hollow fibre cross-section. The effects of the air-gap, viscosity and non-solvent concentration on fibre morphology have been studied and it has been determined that viscosity is the dominating factor for ceramic systems.