Liquid–liquid displacement porosimetry applied to several MF and UF membranes

• LLDP is very useful for optimizing membrane making conditions.
• It allows accurate estimation of performance related capabilities of the membranes.
• UF membranes from an experimental polymer present promising antifouling properties.

Membranes from different commercial polymers (Trogamid® and Radel®) and a new (PAA-g-PEG550) copolymer, consisting of an aromatic polyamide modified with PEG, have been prepared with pore sizes from 0.4 μm to 8 nm. Their porosimetric features have been analyzed by liquid–liquid displacement porometry. In all cases narrower pores are obtained when the polymer concentration in the casting solution increases. Good accordance with image analysis pore sizes is noted. Good correlation is also detected when air–liquid porometry can be used.Permeability decreases always with increasing polymer concentration. Porosity increases when finger like structures are obtained (Trogamid® and PAA-g-PEG550); while, when granular structures are obtained (Radel®), porosity decreases when more polymer is used in the casting procedure.The membrane manufactured from the experimental polymer PAA-g-PEG550 shows high permeabilities and porosities with simultaneous low pore sizes and narrow pore size distributions. The molecular weight cut-off estimated by liquid–liquid porometry agrees well with that found by PEG retention experiments.

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