NAMS 2002 Workshop - ICOM 2008

Ultra- and Microfiltration II - Processes - 6
Thursday July 17, 11:30 AM-12:00 PM, Moloka’i
Pioneering Explorations of Rooting Causes for Morphology and
Performance Differences in Hollow Fiber Kidney Dialysis Membranes Spun
From Linear and Hyperbranched Polyethersulfone
Q. Yang (Speaker), National University of Singapore, Singapore
T. Chung, National University of Singapore, Singapore - chencts@nus.edu.sg
M. Weber, BASF Aktiengesellschaft
V. Warzelhan, BASF Aktiengesellschaft
The adoption of conventional polyethersulfone (PES) material with linear
structure for kidney dialysis membrane application has attracted intensive
attention due to its excellent stability under sterilization, superior bio-compatibility
after the polyvinylpyrrolidone (PVP) modification, and minimal degradation in
membrane performance over extended period of time. On the other hand,
polymers with highly branched structure have also witnessed gaining interests
during the past decade due to their large number of functional groups and high
surface reactivity in contrast to their linear analogues. Although much progress
has been achieved in the structural understanding and the synthesis of
hyperbranched polymers, fundamental understanding and especially industry
application of these hyperbranched polymers are still in infancy. In addition, there
were few studies conducted to systematically compare hyperbranched polymers
properties with their linear analogues, but not to speak of identifying the
differences between hollow fiber membranes spun with the linear and
hyperbranched counterparts.
First of all in this NUS-BASF joint research program, the science and engineering
of hollow fiber membrane formation by a dry-jet wet-spinning technique was
investigated in-depth in order to identify a membrane with desirable structure,
suitable pore size and pore size distribution for kidney dialysis applications. The
dual-bath coagulation technique has been employed for the first time in this study
for fabricating kidney dialysis membranes: with a weak coagulant isopropanol
(IPA) serving as the first external coagulation bath while water as the second
bath, the as-spun membrane can achieve a tight inner selective skin and loose
outer supporting layer structure. This is a desirable membrane structure for
removing low and middle molecular weight uremic toxins such as uric acid, urea,
creatinine, inulin and beta2-microglobulin but retaining proteins molecules during
hemodialysis.
In addition, we have identified that the addition of PVP into the polymer dope
(both linear and hyperbranched PES) during the hollow fiber membrane spinning
could not only provide a macrovoid-free and completely sponge-like structure but