Preparation of supported zirconia ultrafiltration membranes with the aid of polymeric additives

Cracking of ceramic films during drying is a well-known phenomenon. Literatures have shown that films cast on the nonporous substrates will crack unless polymeric additives are added to improve the critic crack thickness. This paper investigates the fabrication of crack-free zirconia membranes on porous substrate through a wet chemical method, with a focus on the influence of polymeric additives on the critical crack thickness and membrane performances. Four types of additives were used in the preparation of zirconia slurries, and polyvinyl alcohol (PVA) and methylcellulose (MC) were favorable for a stable, ready-to-dip-coating slurry suggested by viscosity, particle size distribution and sedimentation measurements. Drying experiments also showed that there was a smooth weight loss and a low risk of crack-formation during membrane drying in the case of using PVA or MC as additives. Compared with a sole polymer additive of 0.75 wt% MC, the critical crack thickness increases from 4.0 μm to 5.0 μm when 0.25 wt% PVA was further introduced into the suspension, which benefits the preparation of crack-free membranes. When the membrane thickness was controlled to be thinner than the critical crack thickness, the prepared membrane would be more likely to have a homogeneous and smooth surface, and less defects or cracks. For the membrane with a thickness of approximately 3-4 μm, the pure water permeability reached 1000 L m^-2 h^-1 bar^-1 and the dextran rejections were up to 85%.