Influence of the concentration and molecular weight of polyethylene glycol on the structure and permeability of polysulfone hollow fiber membranes

Abstract

The influence of the concentration and molecular weight of polyethylene glycol (PEG, 400–40000 g mol^–1) on the phase state and viscosity of ternary polysulfone–polyethylene glycol–N,N-dimethylacetamide solutions has been studied. It was shown that an increase in PEG molecular weight (MW) results in a decrease in the region of existence of homogeneous solutions on the phase diagram due to polymer incompatibility, and in an increase in the viscosity of polymer solutions. At a constant PEG concentration (5%) the viscosity depends on PEG MW in a complicated way: in the range of PEG molecular weights 1000–6000 g mol^–1 the viscosity is nearly unchanged, but when the PEG MW exceeds 6000 g mol^–1 a sharp increase in the viscosity of the polymer solutions is observed. It was shown that changes in the membrane performance are determined by PEG concentration in the dope solution. At a PEG concentration of 5% an increase in PEG MW results in an increase in membrane performance and a decrease in the rejection capability; at an increase in PEG concentration in the dope solution up to 25% the maximum pure water flux was observed for PEG-400. The bubble point test showed that with an increase in PEG molecular weight a fraction of large pores, which can be considered as selective layer defects, increases.