A Novel Manufacturing Process to Fabricate Double-Layer Membranes

A new method to fabricate double-layer membranes by using a specially design casting machine is described in this study. This machine is able to produce membranes with a double-layer structure via a single-casting technique with the use of a closed-loop feedback control system. The membrane casting operation is controlled by a programmable logic controller (PLC). Membranes produced from this simplified technique exhibit similar properties as the double-cast membranes, such as a macrovoid free structure and good porosity property. Results show that high casting speed is desired during the membrane fabrication process as the relaxed polymer molecular orientation and low polymer chain entanglement promote vertical swelling, and hence enhance the membrane porosity. Turbulent coagulant flow further improves the membrane porosity due to the high solvent–coagulant exchange rate during the phase inversion process. In summary, this machine simplifies the double-casting technique and produces membrane with similar advantages as the membrane fabricated via a double-casting technique.     

The observation of elongation dependent macrovoid evolution in single- and dual-layer asymmetric hollow fiber membranes

We have reported, for the first time, that macrovoids in asymmetric hollow fiber membranes may be completely eliminated at high elongational draws. The evolution of macrovoids vs. elongational draw was observed for both single- and dual-layer hollow fiber membranes. The number of macrovoids and the number of macrovoid layer decrease with an increase in elongational draw ratio, while the dimension of macrovoids varies with increasing elongational draw ratio until the macrovoids are fully eliminated. This study indicates that the elongational stress may play a much more important role than our original thoughts on hollow fiber membrane morphology.     

Cellulose acetate (CA)/polyvinylpyrrolidone (PVP) blend asymmetric membranes: Preparation, morphology and performance

Cellulose acetate (CA) membranes are widely used for reverse osmosis (RO) and ultrafiltration (UF) applications. In this study, asymmetric CA membranes were synthesized using phase inversion method. CA with molecular weight of 52,000, polyvinylpyrrolidone (PVP) with molecular weight of 15,000 and 1-methyl-2-pyrrolidone (NMP) were used as polymer, additive and solvent, respectively. The effects of PVP concentration (at 0, 3 and 6 wt.%) and coagulation bath temperature (CBT at 0, 25 and 50 °C) on morphology, contact angle and permeability of the prepared membranes were studied and discussed. It was found out that the effects of PVP concentration and CBT depend on their values.     

Adsorption selectivity of phenylalanine imprinted polymer prepared by the Wet Phase Inversion Method

A phenylalanine (Phe) imprinted polymer was prepared by the wet phase inversion method to investigate the optimum preparation condition which endows the polymer matrix with prominent adsorption selectivity. The addition of a large amount of porogen (dimethyl sulfoxide: DMSO) was needed to form macrovoids in the polymer matrix. For the high adsorption selectivity of the polymer matrix, a complex between functional monomers and a template molecule must be formed before the copolymerization of acrylomtnle (AN: crosslinker) and acrylic acid (AA: functional monomer). The formation of a phenyl group in the polymer matrix by the coupling reaction between D-Phe and AA seemed to cause the reverse adsorption selectivity of the polymer matrix. The adsorption selectivity of the Phe imprinted polymer was dependent on the pH of the racemate solution. The adsorption selectivity of the D-Phe imprinted polymer prepared by the post implanting method reached 11 at pH 2 and showed a reverse adsorption selectivity at pH 4 and 6.