Membrane Formation Technologies
This chapter discusses the individual technologies for industrial manufacturing of microfiltration (MF) or ultrafiltration (UF) membranes. The three main casting technologies—air, immersion, and melt casting—differ primarily in the methods used for desolvation, and the equipment used. The chapter attempts to cover some more unique, "special case" technologies for industrial-scale production of MF/UF membranes. Historically, air casting is the oldest technology for manufacturing MF membranes. Immersion casting is probably the most widespread technology for manufacturing both MF and UF membranes. A considerable effort has been devoted toward development of appropriate theoretical ternary mass-transfer models for the desolvation stage of immersion casting. Gelation and demixing usually occur concurrently with desolvation during membrane formation. The combination of rapid desolvation kinetics with relatively slow rates of polymer crystallization is responsible for nonequilibrium effects, which are frequently observed in melt casting. Among the advantages of the track-etched filters, one can list structural simplicity and ease of characterization, non-hygroscopicity, surface flatness, and transparency.