Upgrading polyamide TFC BWRO and SWRO membranes to higher SWRO membrane performance via surface nano-structuring with tethered poly (acrylic acid)

Polyamide (PA) thin film composite (TFC) BWRO and SWRO membranes were surface nano-structured (SNS) with tethered hydrophilic poly(acrylic acid) (PAA) layers. BWRO and SWRO membranes having water (L-p) and salt (B) permeability coefficients in the ranges of 2.3-3.4 L m(-2) h(-1) bar(-1) and 0.15-0.54 L m(-2) h(-1), respectively, were utilized as base membranes onto which tethered PAA layers were synthesized via acrylic acid (AA) graft polymerization (GP), post-membrane surface activation with atmospheric pressure plasma (APP). Both APP surface activation and GP conditions impacted SNS-PAA-PA membrane performance evaluated in terms of the membrane L-p and B parameters. Surface structuring with a tethered PAA layer enabled tuning of membrane performance (in terms of L-p and B) to achieve water/salt selectivity (evaluated as L-p:B ratio) that was significantly higher (by up to 56%) relative to the base PA membranes. Depending on APP surface activation and AA graft polymerization conditions, membranes could be tuned to have essentially the same salt rejection over a range of permeability or a given permeability over a range of salt rejection. It was also shown that a membrane performance could be achieved that overcomes the permselectivity tradeoff.