Modified poly(phenylene oxide) membranes in ultrafiltration and micellar-enhanced ultrafiltration of organic compounds

Poly(phenylene oxide) (PPO) membranes with sulfonic groups were prepared by two methods: plasma-initiated surface grafting of sodium styrenesulfonate or chemical sulfonation (with chlorosulfonic acid) of PPO, followed by membrane preparation from the modified material. The presence of ionic groups greatly increased the surface polarity of the material and the flux of water through the membranes. It seemed, however, not to improve the protein filtration process. Coating of these membranes with allylamine plasma polymer resulted in amphoteric membranes much better for ultrafiltration than those made of unmodified PPO. Such bipolar membranes appeared to be also very effective in micellar-enhanced ultrafiltration of mixtures of the 2,4-D herbicide and hexadecyltrimethylammonium bromide.

Both investigated methods of introduction of sulfonic groups into membranes were efficacious, namely plasma initiated surface grafting of NaSS and chemical sulfonation (with chlorosulfonic acid) of PPO, the latter giving the higher sulfur concentration on the surface of the membranes. Sulfonated materials are much more hydrophilic (polarity from 20 to 50%) than PPO (5%). PPO membranes grafted with NaSS do not demonstrate improved properties in the BSA filtration process. However, deposition of allylamine pp on their surface gives bipolar, amphoteric membranes with much improved filtration capacities. The second type of bipolar membranes made from PPO sulfonated in bulk perform very well in the MEUF process, removing more than 90% of 2,4-D herbicide from water.