Fabrication and Characterization of PAA-g-PES Polymers and Resultant Membranes: Combating Fouling through the Introduction of Hydrophilic PAA Brushes

The adoption of polymeric membranes for reclamation of natural organic pollutant-impacted water has been of recent interest. However, membrane fouling has been an obstacle in the application of membranes over a longer period. Fouling, which is mainly caused by organic materials, is a universal challenge in membrane technology for water treatment. The hydrophobic nature of poly-(ether sulfone) (PES) membranes has a high affinity toward organic compounds. To elevate this challenge, in this study, hydrophilic brushes of poly-(acrylic acid) (PAA) were grafted onto the PES backbone using free radical graft polymerization. The successful grafting of PAA brushes on PES was confirmed through characterization using Fourier transform infrared spectrophotometry, 1H NMR, 13C NMR, and thermogravimetric analysis, with a grafting yield ranging from 2.11 to 6.7%. The thermal stability, functionalities, morphology, wettability, and surface roughness of the PAA-g-PES membranes were also investigated as these characteristics play an important role in the overall performance of the membrane system. The improved hydrophilicity was seen through the observed decrease in the membranes' water contact angle (77° for the pristine PES membrane to 46° for the highest modified PAA-g-PES membrane) in response to the increased PAA content. The antifouling propensity of the fabricated PAA-g-PES membranes was tested through the seven-cycle fouling-backwashing processes using bovine serum albumin (BSA) model protein as well as the river water sourced from Centurion, South Africa, as the feeds. It was observed that the flux recovery percentages after the seventh cycle (6.5 h) were 20.7 and 25.5% for the pristine PES membranes and 55.3 and 59.8% for the PAA-g-PES membrane with the highest grafting yield for the BSA-laden water and the river water, respectively. The improved recovered flux suggests that the PAA-g-PES properties enhanced the fouling resistance of the modified membranes, giving the membranes a better chance of applicability in a real-life filtration system.