Improved performance of novel bulky polysulfone versus conventional polysulfone as substrate in thin-film composite membrane

In this study, the structure-property-performance relationship was evaluated in a novel polysulfone structure used as a porous substrate for thin-film composite membrane and compared with the common polysulfone structure. Both polysulfones were prepared via nucleophilic aromatic substitution polycondensation reaction of different bisphenols with difluorodiphenyl sulfone. The structural impact of polysulfones on substrate properties and performance of the related thin-film composite membranes were investigated. The new structure had a phenyl group instead of a methyl group in the common polysulfone structure. The existence of bulky phenyl substituent in the backbone of new polysulfone resulted in additional free volume. The new substrate revealed larger pore size and porosity, and higher roughness compared to the common substrate. From another point of view, the extra aromatic ring of this substrate led to more pi- pi interactions with aromatic rings in the polyamide layer, resulting in more uniformity and regularity for thin-film formation. The prepared new rougher thin-film composite membrane exhibited water permeance of 4.21 L m-2 h-1.bar-1 and salt rejection of 97.99 % at 15 bar applied pressure with 2000 ppm NaCl feed solution at 300 min measurement. About 21 % increase in water permeance was observed compared to the common thin-film composite membrane, as well as slightly increase in salt rejection. The results of this study established a practical starting point for the progress of a new polysulfone substrate for reverse osmosis desalination.