Dual-action comb-shaped amphiphilic polymers as novel cleaning agents for efficient cleaning of organic-fouled RO membranes

This study presents the facile synthesis of environmentally benign, comb-shaped amphiphilic polymers for cleaning organic-fouled reverse-osmosis (RO) membranes. The polymers comprise a hydrophobic polymaleic anhydride (PMA) backbone with hydrophilic oligoethyleneamine side chains; the amine content of the polymer was tuned by varying the side-chain lengths: triethylenetetramine (TETA), tetraethylenepentaamine (TEPA), and pentaethylenehexamine (PEHA). Static cleaning of age-hardened, heavily fouled plant membranes identified TEPA as effective at 2.5 g/L, pH 11.5, and 40 °C. For dynamic tests, commercial membranes were fouled with sodium alginate to ∼50% flux decline and then cleaned using standard protocols. Among the varying amine content, the polymer with PEHA as the side chain exhibited the highest cleaning efficiency, achieving ∼95% flux recovery, and restoring the original membrane hydrophilicity and the peak-valley polyamide morphology, as confirmed by contact angle, Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM). Surface analysis of the PEHA polymer cleaned membrane using Energy-Dispersive X-ray (EDX) indicated surface chemistry similar to that of the pristine membrane. The influence of pH and temperature on the cleaning efficacy was evaluated: PEHA was observed to be the most effective in the pH range 9.5–11 and at a cleaning temperature of 40 °C. A dual mechanism for cleaning is proposed: (i) solubilization and detachment of polysaccharide foulant via electrostatic complexation and hydrogen bonding between cationic polymer groups and foulant carboxylates; and (ii) Ca²⁺ chelation that disrupts cation-bridged alginate layers. Overall, the use of comb-shaped amphiphilic polymers offers an effective and eco-friendly approach to RO membrane cleaning under milder conditions.