Surface Properties of a Reverse Osmosis Membrane Undergoing Grafting Process

Radical grafting of acrylic acid (AA) monomer onto the aromatic polyamidereverse osmosis (APRO) membrane was performed. The physical adsorption byfree radical initiator technique was applied to modify the surface of theasymmetric membrane. The hydrophobic initiator adsorbed on the APRO membranewas used to initiate the water-soluble monomer in aqueous phase. The APROmembrane was immerged into ether solution of benzoyl peroxide (BPO). The BPO wasphysically adsorbed onto the membrane surface. The hydrophobic initiator wasinhibited to diffuse through membrane surface into the aqueous solution of the acrylicacid monomer because of a hydrophilic/hydrophobic barrier. The grafting process wastriggered by the residing BPO on the membrane surface in an aqueous medium at70°C for a certain time interval. The surface changes of grafted membrane werecharacterized with ATR-FTIR, SEM, AFM and contact angle measurements. The resultsshowed the PAA is successfully grafted on the APRO membrane surface. When thegrafting rate of PAA was increased from 0% to 8.02%, the edge of leaf-like surface ofAPRO membrane was gradually curled and the roughness of APRO membrane wasdecreased about 36% (Ra). These changes of membrane surface increased thehydrophilicity of the APRO membrane surface and the contact angle decreased byabout 50%.