Asymmetric membranes with controlled morphology from modified polyetheretherketone (PEEKWC): preparation and characteriz
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Asymmetric membranes with controlled morphology from modified polyetheretherketone (PEEKWC): preparation and characterization. M.G. Buonomenna, A. Figoli, J.C. Jansen, M. Davoli1 and E. Drioli Institute of Membrane Technology (ITM-CNR), c/o University of Calabria, Via P. Bucci, Cubo 17/c, 87030 Rende (CS), Italy. 1 University of Calabria, Department of Earth Science, Via P. Bucci, Cubo 14/b, 87030 Rende (CS), Italy. INTRODUCTION PEEKWC is a high performance thermoplastic modified polyetheretherketone [1-2]. This polymer, like the traditional PEEK, presents excellent thermal resistance, high chemical stability and good mechanical properties. In addition, in contrast to PEEK, it is well soluble in various common solvents. Few studies have been published on PEEKWC as a membrane forming material [3-4] but no systematic studies on the relationship between morphology and preparation conditions have been reported yet. O In the present work, the preparation and O O characterization of PEEKWC membranes by the Nonsolvent Induced Phase Separation (NIPS) technique are described. The influence of the O O O n polymer concentration in the casting solution and PEEKWC different nonsolvent/solvent combinations on the membrane morphology and transport properties have been studied. The solvents used for membrane preparation are N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA) and tetrahydrofuran (THF); water was used as the nonsolvent. The membranes were characterized by means of Scanning Electron Microscopy (SEM), pure water flux, bubble point and gas permeation. EXPERIMENTAL DETAILS Materials. PEEKWC was supplied by the Chanchung Institute of Applied Chemistry, Academia Sinica. The polymer powder was purified by Soxhlet extractor with methanol and then dried in a vacuum oven. All solvents, were purchased from Fluka and used without purification. Phase diagrams. Phase diagrams were determined by visual observation of the cloud point during slow addition of water or a water/solvent mixture to the stirred polymer solution at room temperature (ca. 20°C). After the cloud point was reached, a small amount of extra water was added and then the opposite procedure was followed: determination of the point where the solution became clear again by slow addition of solvent (‘clearing point’). This entire procedure was repeated several times until the system became too dilute for accurate observation of the turbidity changes. Membrane preparation and characterization. The purified polymer was dissolved (10 and 15 wt.% in DMF, DMA and THF) at room temperature by magnetic stirring for at least 1 day. The casting solutions were then centrifuged to remove macroscopic impurities. The solutions were cast uniformly onto a glass substrate by a hand-casting knife (BRAIVE Instruments) with a knife gap of 250 µm and immersed in a water coagulation bath. An overview of the experimental conditions is reported in Table 1. The morphology of the membranes, dried at 60°C overnight, was examined by SEM (Cambridge, Stereoscan 360). The membrane thic
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