The Modification of Polyethersulfone Membranes Using a Synperonic F108 Block Copolymer and Their Application for the Fractionation of Thermomechanical Pulp Mill Process Water

The effect of additions of a Synperonic F108 amphiphilic triblock copolymer of poly(ethylene oxide) and poly(propylene oxide) to casting solutions on the structure and properties of polyethersulfone (PES) membranes was studied. It is found that the introduction of small amounts (0.3-0.5%) of Synperonic F108 leads to an increase in the pure water flux of membranes from 50 up to 120-200 L m(-2)h(-1)at the same time membranes showed constant selectivity and enhanced hydrophilicity. The water contact angle decreases from 65 degrees down to 41 degrees-42 degrees. Infrared (IR) spectroscopic studies show that Synperonic F108 is predominantly localized on the selective layer of membranes. The investigation of the morphology of membranes by scanning electron microscopy (SEM) shows that the introduction of Synperonic F108 promotes an increase in the total width of the transition layer and suppressed the macrovoids formation in the membranes supporting layer. Modified membranes are tested in the process of fractionation of thermomechanical pulp mill process water in order to isolate hemicelluloses for further processing. It is shown that the modified membranes obtained with the addition of 0.5% Synperonic F108 are characterized by two- to sixfold higher flux and 40% higher flux recovery ratio. The hemicellulose rejection for the initial and modified membranes varies within 95-97%, while lignin rejection is slightly lower in the case of modified membranes (14-19%, 21% for the nonmodified membrane).