The role of the nature of the casting substrate on the properties of membranes prepared via immersion precipitation

The role of the nature of five different casting substrates on the properties of the resulting polysulfone membranes has been investigated. Wetting of the NMP-based polymer dope on the casting substrate has been quantified and linked to shrinkage of the membrane during the spreading and the coagulation phase of the wet phase inversion process. Shrinkage was found to less important when cast on hydrophilic substrates. Addition of a ZrO2 filler to the casting dope decreased the degree of shrinking. These data were then correlated to permeabilities and MWCO-values. The latter decreased upon casting on hydrophobic surfaces and the retention curves became sharper and less pressure dependent. FESEM-pictures of the membrane surfaces in combination with image analysis allowed to conclude that the diameter of the surface pores was surprisingly not influenced by the casting substrate. Casting on a Teflon support decreased the surface porosity.