A high flux ultrafiltration membrane spun from PSU/PVP (K90)/DMF/1,2-propanediol

Hollow fiber ultrafiltration (UF) membranes have been made from a new dope solution containing polysulfone (PSU)/poly(vinyl pyrrolidone) (PVP) (K90)/N,N-dimethylformamide (DMF)/1,2-propanediol (1,2-PD) with a mass ratio of 15:5:77:3 by using a dry-jet wet spinning process. The membranes were post-treated by means of a hypochlorite solution over a range of concentration for a fixed period of 48 h. The experimental results showed that the fluxes of all treated membranes were 4.0–5.4 times greater than that of an untreated membrane. The retentions of treated membranes for the solutes of molecular mass less than 67 kg mol−1 were much lower than that of an untreated membrane. There was an optimum hypochlorite concentration with this post-treatment to achieve a membrane with a high flux and narrow pore size distribution. In addition, the scanning electronic microscopy (SEM) images clearly showed an inner dense skin layer of thickness less than 0.4 μm after hypochlorite treatment and PVP contents in the blend membrane could be removed with the hypochlorite treatment. As a result, the untreated membrane showed very low fouling tendency due to the hydrophilic nature of the PVP/PSU blend, but the treated membrane experienced a significant fouling tendency due to much reduced hydrophilicity. It was concluded that a dope formulation being very close to its cloud point (binodal line) would result in a membrane with a thin skin and high flux. A PSU UF membrane with flux of 760×105 l m−2 h−1 Pa−1 could be obtained through hypochlorite treatment and the hypochlorite treatment altered the pore size and pore size distribution of a PSU UF membrane while eliminating the swelling of PVP. The latter observation differed from published results and an attempt at explaining the difference was offered.