Measuring Pore Size in the Walls of Hollow Fiber Membranes
Hollow fiber and capillary membranes have a number of attractive properties such as flexibility, high surface area per unit volume, and unique packaging opportunities, which means they can be adapted to a variety of filtration applications. However, their physical form makes it challenging to measure the sub-micron size pores within the walls. A preparation procedure for measurement via capillary flow porometry and examples of different hollow fiber samples measured on the Porometer 3G series are reported.
The excellent mass transfer properties of the hollow fiber construction (a relatively large lumen surrounded by a large area of a thin porous membrane wall) has led to it being utilized in numerous commercial applications in widely different fields such as medical (blood fractionation), water reclamation (purification and desalination), gas separation, and techniques using pervaporation. Other promising applications of this type of membrane are in the biochemical industry (bioseparation and bioreactors). Specifically, its beneficial features, compared with more traditional filtration and separation systems, are modest energy requirements, high volume efficiency, two modes of operation (inside-out and outside-in) and low operation costs. To a certain extent, these benefits are offset by more frequent fouling and initial capital expense.
The challenge faced by those needing to determine the pore size distribution through the walls is to find a technique which can functionally transfer a fluid radially through a narrow fiber; by comparison, measurements across a flat sheet are simple. The difficulty of analyzing hollow fibers has been overcome by a special preparation technique which involves sealing an individual fiber into a special sample holder and analyzing the pore size via capillary flow porometry.
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