Effect of molecular weight and concentration of PEG on ultrafiltration membrane morphology structure

MERCEDES L. MÉNDEZ; VERÓNICA B. RAJAL; ELZA CASTRO VIDAURRE; LAURA PALACIO; JOSÉ I. CALVO; ANTONIO HERNÁNDEZ

Amsterdam

Congreso; International Congress on Membrane and Membrane Processes.; 2011

INTRODUCTION:Asymmetric UF membranes synthesized from the phase inversion method are affected by many factors, which could result in significant changes, especially on selectivity and permeability of the resulting filters. Among those factors there could be included: polymer, solvent, non solvent, additives and synthesis conditions. In the present work, polyethersulfone (PES) membranes were prepared using polyethylene glycol (PEG) as additive, with several values of Molecular weight (400, 1000 and 10.000 Da) and concentration (12, 15 y 20 wt %), being dimethylacetamide (DMAc) the solvent. The objective was to determine how the additive used affects the membrane morphology comparing results with similar polymeric systems, [1-2]. During the synthesis process the non-solvent used was a water bath.Membranes were characterized using contact angle to determine the effect of additive on the surface hydrophilicity. Also SEM images have been used to know the membrane morphology and Liquid-liquid Displacement Porosimetry (LLDP) was used to quantify the pore size distributions, [3].RESULTS:SEM images showed a gentle reduction of macropores present in the substructure of the membranes, as the molecular weight of the additive increase for each concentration. Addition of PEG resulted in a contact angle decrease (from 73,9° to 40-50º), so indicating a higher surface hydrophilicity (), surely due to the presence of PEG chains entrapped between PES molecules, as explained for other additives, [4]. Results from LLDP show that for most of the cases the mean pore size of the resulting membranes decrease as additive molecular weight increases.[figure1]CONCLUSIONS:The increase on hydrophilicity due to the addition of PEG is strongly favourable as resulting in increased membrane life and reduction of membrane fouling tendency. Usually increase of MW and concentration of PEG results in lower mean pore size maintaining constant permeabilities. This combination increases membrane selectivity.REFERENCES:[1] Chakrabarty, B., A.K. Ghoshal, and M.K. Purkait, Effect of molecular weight of PEG on membrane morphology and transport properties, J. Membrane Sci., 309 (2008) 209-221.[2] Idris, A., N. Mat Zain, and M.Y. Noordin, Synthesis, characterization and performance of asymmetric polyethersulfone (PES) ultrafiltration membranes with polyethylene glycol of different molecular weights as additives. Desalination, 207 (2007) 324-339.[3] J. I. Calvo, R. I. Peinador, P. Prádanos, L. Palacio, A. Bottino, G. Capannelli and Antonio Hernández, Liquid–liquid displacement porometry to estimate the molecular weight cut-off of ultrafiltration membranes, Desalination, 268 (2011) 174-181.[4] J. Marchese, M. Ponce, N. A. Ochoa, P. Prádanos, L. Palacio and A. Hernández, Fouling behaviour of polyethersulfone UF membranes made with different PVP, J. Membrane Sci., 211 (2003) 1-11.