(657b) Calculation of Phase Diagrams of Polyetherimide/N, N-Dimethylacetamide/Nonsolvent Casting Systems and Prediction of Performances of Ultrafiltration Membranes

Calculation of phase diagrams
of polyetherimide/N, N-dimethylacetamide/nonsolvent casting systems and prediction
of performances of ultrafiltration membranes

Ming
Tan, Gaohong He[*],
Yan Dai, Rujie Wang, Junli Xiao

State Key Laboratory of Fine Chemicals, R&D Center of Membrane
Science and Technology, School of Chemical Engineering, Dalian
University of Technology, Dalian, 116024

Abstract: Polyetherimide (PEI)/N, N-dimethylacetamide
(DMAc) ternary phase diagrams with nonsolvent (NS) of H₂O, polyethylene
glycol (PEG400) and 1-butanol (BuOH)
were calculated
by using Hildebrand and Hansen solubility parameter and Flory-Huggins theory. The
phase diagrams indicate that it should use Hansen solubility parameter and correct
constant ¦Á of 1 to calculate interaction parameters of NS/DMAc/PEI casting
system, and then the interaction parameter between BuOH solution and PEI was computed. Besides,
PEI/DMAc/H₂O-BuOH quaternary phase diagram was
simulated, which is consistent with the experimental cloud points. The phase
diagrams show that when volume ratio of BuOH to H₂O is 9.327, 5.5% BuOH solution consisted of 5%
BuOH and 0.5% H₂O leads to phase
separation of 15-20wt.% PEI
casting solution. Simultaneously, when volume ratio of BuOH to H₂O
is 22.86, 6.5% BuOH solution including 6.2% BuOH and
0.3% H₂O brings on phase separation
of the casting solution. Therefore, additive BuOH can enhance the phase
separation of the PEI
casting solution and hereby induce higher porosity of the membrane. Moreover,
molecular size of BuOH is bigger than DMAc. Hence, compared with DMAc, diffusion
of BuOH into the water coagulation bath causes larger pore size. However, when
additive BuOH increases to a certain value, the greatly increased viscosity of
the casting solution hinders the outlet of the solvent DMAc, additive and inlet
of the nonsolvent water and thereby causes a thicker skin layer. As a result, it
can be predicted that membrane PWF first increases then decreases, and RR
decreases with the increases of BuOH concentration. The prepared membranes
validated our predictions.

Key words: phase
diagram; solubility parameter; interaction parameter; ultrafiltration; Flory-Huggins