Macrovoids asymmetric hollow fiber membranes

The formation of macrovoids in these asymmetric polyaniline hollow fibers is undesirable as they weaken the mechanical strength and may lead to defects in the selective layer, which make them nonviable for many separations applications. The formation of macrovoids in hollow fiber membranes is generally caused by fast precipitation kinetics of the polymer solution in the coagulation bath. The formation of macrovoids when spinning polyaniline hollow fibers was foimd to be highly dependent on... 

Wang, K. Y., Li, D. R, Chung, T. S., and Chen, S. B. (2004a). The observation of elongation dependent macrovoid evolution in single- and dual-layer asymmetric hollow fiber membranes. Chem. Eng. Sci. 59, 4657. 

Widjojo, N., and Chung, T. S. (2006). The thickness and air-gap dependence of macrovoid evolution in phase-inversion asymmetric hollow fiber membranes. Ind. Eng. Chem. Res. 45, 7618. 

FIGURE 15.7 Schematic diagram for macrovoid growth. (Adapted from D. Li, Duallayer asymmetric hollow-fiber membranes for gas separation, PhD Thesis, Chemical Biomolecular Engineering, National University of Singapore, Singapore, 2005.)... 

Microfiltration and UF membranes can be asymmetric, with a denser side and a more open side, or uniform without macrovoids (See Figure 16.3). The open area behind the denser surface in an asymmetric design means there is less resistance to water permeating the membrane. Operating pressure can be lower and the membrane systems can be more productive. The limitation of the asymmetric design is that the material, predominately used in the hollow fiber configuration, is not as strong as the uniform cross section. 

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