A novel positively charged asymmetry membranes from poly(2,6-dimethyl-1,4-phenylene oxide) by benzyl bromination and in situ amination: Part II: Effect of charged group species on membrane performance and morphologies

Positively charged membrane with various charged groups were prepared by in situ amination and phase inversion in which the amine-organic solution and bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) was cast and immerged into an ethanol coagulation bath. The separation performance and morphologies were examined to investigate the effect of hydrophilicity of charged groups on the selective properties and the structure formation of the membranes. Positively charged groups introduced in the membranes were trimethylbenzylammonium, triethylbenzylammonium, tri-n-propylbenzylammonium and tri-n-butylbenzylammonium, in order of increasing hydrophobicity. Pure water flux and rejection to gelatin of the membranes at three pH values changed remarkably with increasing chain length of alkyl groups. The tendency of the change was mainly explained by coagulation value of the casting solution. The streaming potential and ion exchange capacity of the membranes were determined and the results showed that the membranes were all positively charged. Furthermore, water content, pore size distribution and SEM images of the membranes were examined as well.