Sugar fractionation using surface-modified nanofiltration membranes

Nanofiltration (NF) membranes were prepared using layer-by-layer (LbL) deposition of poly(sodium 4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC) on polysulfone (PSf) ultrafiltration (UF) membranes. The feasibility of using these NF membranes for fractionation of sugars was investigated. Deposition of polyelectrolyte multilayer (PEM) on the PSf membrane substrates was also confirmed by various characterization methods. Characterization results along with NF tests confirmed that pore-filling took place for 50 and 100 kDa PSf membranes. Results show that modified membranes were capable of separation/rejection of compounds with molecular weights in the range of mono- and disaccharide solutes. The 50 kDa base UF membrane modified with [PSS/PDADMAC]₇PSS showed the best NF performance with sucrose to glucose selectivity of more than 11. In order to further enhance the separation factor and ensure a stable modification of the membrane, a novel method to convert the ionic bonded coatings into covalently bonded coatings has been developed.