NAMS 2002 Workshop - ICOM 2008

ease of manipulation as this allows the desired morphology of the membranes to
be attained via phase inversion followed by further crosslinking on the pre-formed
membrane to maintain this morphology in aggressive conditions. In OSN, where
membrane stability of the under-layer is as critical as the separating layer,
effective and uniform crosslinking of the whole membrane must be achieved.
This suggests the use of radical initiated methods which would have difficulty of
achieving crosslinking throughout the whole membrane. Instead, we chose
chemical crosslinking as the preferred method to achieve uniform crosslinking
throughout the membranes. Several chemical crosslinking strategies for use in PI
membranes have been proposed and include the use of di/poly-amines in a ring
opening reaction [4] and the inclusion of condensable crosslinking sites during
polymer preparation.
A range of solvent stable organic solvent nanofiltration membranes were
prepared through the chemical crosslinking of preformed integrally skinned PI
membranes using aliphatic diamines. The resultant membranes had a spongy
structure and were stable in many organic solvents including toluene, methanol,
acetone, DCM, THF, DMF and NMP. The further development of the membrane
into spiral wound elements was undertaken, involving scaling up the membrane
production process and then developing spiral wound elements that are stable in
aggressive solvents. Extended periods of both flat-sheet and spiral-wound
element testing in DMF and THF for e120 h showed that the membranes and
elements have a stable flux and good separation performance, with DMF
permeability in the range of 1-8 L m -2 h -1 bar -1 and Molecular Weight Cut-Off
(MWCO) between 250-1000 g mol -1 . However possible re- imidization and loss of
crosslinking at elevated temperatures limits their range of application to
temperatures