the role of polymeric additives on the morphology and performance of a porous layer of nanofiltration composite membranes based on polyether sulfone

the role of polymeric additives such as pvp and peg is studied with respect to the morphology of pes porous layer as a sublayer of nanofiltration composite membranes based on pes/pa. results show that by phase inversionprocess of quaternary systems comprised of four components of polymer/solvent/non-solvent/additive and the diffusion of intertwined polymers some changes occur in membrane morphology with changes in their concentration. with addition of pvp, tear-like pores, finger-like and channel-like morphology change to enlarged channel cavities and by adding more pvp, membrane morphology changes further and spongy regions are extended in the membrane. presence of peg in casting solution delayed the precipitation time. by adding peg, the solution viscosity is increased which is followed by decreases in diffusion rates of solvent/non-solvent in coagulation bath.therefore, membrane morphology shifts to small pores and spongier region. another effect of increased peg content would be deformed pa layer formation in pes sublayer which affects membrane performance. however, pvp as an additive does not change membrane salt rejection very much while it leads to higher fluxes. a membrane with 2.5 percent pvp would perform by 40 percent flux increases, while a membrane with 5% pvp shows flux reductions even below the initial value. contrary to pvp, the peg content of 20 percent leads to 4 folds flux increases and in a membrane with 50 percent peg, there is a flux increase by 7 folds and drop in salt rejection occurs by 50 percent and 70 percent, respectively.