Effect of heat treatment on the performance and structural details of polyethersulfone ultrafiltration membranes

Abstract

In this paper, the effect of heat treatment on polyethersulfone membranes is presented. Generally, a small change in membrane structure has a drastic effect on membrane performance. Ultrafiltration (UF) flat sheet membranes were prepared from casting solutions containing 20 wt% polyethersulfone (PES), 65 wt% N,N-dimethylformamide (DMF), and 15 wt% polyethylene glycol 200 (PEG 200) by phase inversion method. The membranes were then heated in air at various temperatures ranging from 50 to 150°C. The membrane performance was initially evaluated in terms of pure water permeation and solute separation using PEG 35000 Daltons solution. Next, the molecular weight cut off (MWCO) of PES UF membranes were then determined by further UF experiments using 1000 ppm polyethylene glycol (PEG) solution of various molecular weights ranging from 1000 to 35 000 Dalton. Mean pore size (µp) and standard deviation (óp) of the membranes were determined from solute transport data. It is observed that solute separation using PEG 35000 Daltons increased while flux decreased as the heating temperature increases. The MWCO and pore size of the membranes decreased with increased heating temperatures. Surface and cross section of PES UF membranes were characterized before and after heating using Scanning Electron Microscope (SEM). Atomic Force Microscopy (AFM) analysis revealed significant changes were observed in the surface of PES UF membrane with increased heating temperatures. The performance of the membrane was not only affected by heat treatment but also the heating temperatures.