(243d) Fundamental Understanding of the Morphology and Macrovoid Evolution of the Single-Layer P84 and Dual-Layer Ultem/P84

Single-layer P84 and dual-layer Ultem/P84 hollow fiber membranes with different morphology have been fabricated simultaneously via a dry-jet wet-spinning process. A preliminary study of the effects of spinneret dimension and its coupling effect with air- gap distance on macrovoid evolution in the single-layer P84 hollow fibers show that the number of macrovoids considerably increases with an increment in spinneret annulus gap thickness. In addition, the number of inward-pointed macrovoids increases while the number of outward-pointed macrovoids decreases with an increase in air-gap distance. Based on the study of single-layer P84 hollow fiber membranes, the desired dual-layer Ultem/P84 hollow fiber membrane morphology with a sponge-like outer layer and free-macrovoid inner layer structures for pressure-driven process applications can be tailored by determining a proper combination of air gap distance, first external coagulant, and bore-fluid chemistry. It is found that dual-layer hollow fiber membranes spun with a longer air-gap and a first coagulant bath using higher alcohol series, i.e. ethanol or 2-propanol are more prone to a closed-cell structure formation as compared to those spun with a lower air-gap and a first coagulant bath using water or methanol. Furthermore, the number of macrovoids in the inner layer increases with an increase in air-gap distance which is similar to the phenomenon found in the single-layer hollow fiber membranes. In addition to the air-gap length, the type of the first coagulation bath and bore-fluid also has a significant impact to the formation of macrovoids in the inner layer.