Contribution of polysulfone membrane preparation parameters on performance of cellulose nanomaterials

Abstract

Nowadays, nanocomposite mixed-matrix membranes (NMMMs) have gained considerable attention in many applications and research fileds. In this study, NMMMs composed of polysulfone (PSf) and cellulose nanomaterials (CNMs), i.e. cellulose nanocrystals (CNC) or cellulose nanofibers (CNF), were prepared using immersion precipitation (IP) or vapor-induced phase separation (VIPS) techniques. CNM contents of 0, 0.2, 0.5 and 1.0 wt% with respect to the PSf weight, PSf concentrations of 20 and 30 wt% and casting thicknesses of 50, 100 and 200 μm were considered for preparation of PSf-CNM NMMMs. The membranes were characterized with respect to cross-section and top surface moprhologies, pure water flux (PWF), porosity characteristics and their potential to purify methylene blue (MB) wastewater. Results pointed to slight effect of CNM type on PWF of PSf-CNM NMMMs. It was demonstrated that PSf membrane preparation parameters including membrane preparation technique, dope concentration and casting thickness, highly contribute to the modification performance of CNMs. Irrespective of the preparation technique, the highest PWF was reached at optimum CNC content of 0.5 wt%. For membranes prepared using IP technique at 200 μm casting thickness, CNC content of 0.5 wt% yielded to PWF increase from 2.5 to 10.6 L.m-2.h-1 (by 324.0%) and from 0 to 2.6 L.m-2.h-1, respectively, for PSf concentrations of 20 and 30 wt%. When PSf concentration was 30 wt%, for 50, 100 and 200 μm casting thicknesses, the highest increases in PWF, i.e. from 8.4 to 22.9 L.m-2.h-1 (by 172.6%), from 0.0 to 6.1 L.m-2.h-1 and from 0.0 to 4.6 L.m-2.h-1, were achieved at CNC contents of 0.5 wt%, 1.0 wt% and 1.0 wt%, respectively. CNC content positively affected MB rejection efficiency. PSf-CNC NMMM prepared under conditions of PSf concentration of 30 wt%, CNC content of 0.5 wt% and 50 μm casting thickness, possesses the highest PWF (22.9 L.m-2.h-1) and MB rejection efficiency (98.1%).