Cellulose acetate hollow fiber ultrafiltration membranes made from CA/PVP 360 K/NMP/water

Abstract

Hydrophilic hollow fiber ultrafiltration (UF) membranes have been prepared from a new dope solution containing cellulose acetate (CA)/poly(vinyl pyrrolidone) (PVP 360 K)/ N-methyl-2-pyrrolidone (NMP)/water with a mass ratio of 19.0/5.0/74.8/1.2 by using a dry-jet wet spinning process. The effect of air-gap length was studied. The as-spun fibers were post-treated by means of a hypochlorite solution of 200 mg l −1 (200 ppm) over different duration. The morphology of the membranes was investigated by Scanning Electron Microscopy (SEM). Pure water fluxes and solute retentions of the membranes were measured and different fouling resistances were analyzed. The experimental results showed that water flux of a membrane decreased while retention increased with increasing air gap. Fluxes of hypochlorite treated membranes were three times higher than that of an untreated membrane and retentions of the treated membranes were much lower. A 6 h treatment with 200 mg l −1 hypochlorite solution could achieve a CA UF membrane with a high pure water flux of 220×10 −5 l m −2 h −1 Pa −1. SEM images revealed that, PVP additive would favor the suppression of macrovoids and the thickness of inner skin increased with increasing air gap. PVP contents in the blend membrane could be significantly removed with the hypochlorite treatment. As a result, the treated CA membrane experienced higher fouling tendency than the untreated membrane. It was concluded that hypochlorite treatment altered the pore size of hollow fiber UF membranes made from the blend of CA and PVP 360 K. This is an extended conclusion to the published results and an attempt at explaining some differences were provided.