The development of novel micro-capillary film membranes

This paper reports the experimental results for the processing of micro-capillary film (MCF) membranes. MCFs are films with embedded multiple hollow capillaries and can be considered as a hybrid geometry between flat sheet and hollow fibres. Compared to the conventional membrane geometries, MCFs potentially provide a higher surface area per unit volume, better mechanical strength, ease of handling and more efficient module fabrication. MCF membranes were fabricated out of ethylene vinyl alcohol (EVOH) copolymer through a solution extrusion followed by a nonsolvent induced phase separation process (NIPS). Single capillary EVOH membranes were also fabricated prior to the fabrication of MCFs to establish a base process. Fluid flow observations were carried out at different regions in the process in order to better understand the dynamics of extrusion and phase inversion. It was observed that polymer solution and bore fluid rheology as well as processing conditions including air-gap distance and take up rate have significant effects on the flow dynamics and consequently the macrostructure of the membranes. Furthermore, the flow observations led to the identification of an extrudate expansion phenomenon in the external coagulation bath which strongly influenced the membrane formation process. The micro-structure characterization of the fabricated membranes showed the formation of a highly porous, interconnected and macrovoid-free microstructure in the membranes. MCF membranes can be applied with a potentially promising performance in a variety of membrane applications such as micro and ultrafiltration, membrane bioreactors (MBR), porous microfluidic devices as well as membrane contactors for process intensifications.

► Development of membranes in a novel micro-capillary film (MCF) geometry is reported.
► Flow observations were carried out to better understand the process.
► The effect of processing conditions on the MCF membrane macrostructure was studied.
► Air-gap distance and take-up rate significantly influence the MCF fabrication process.
► An extrudate expansion phenomenon was discovered in the process and explained.