Surface Properties of a Reverse Osmosis Membrane Undergoing Grafting Process

Radical grafting of acrylic acid (AA) monomer onto the aromatic polyamide reverse osmosis (APRO) membrane was performed. The physical adsorption by free radical initiator technique was applied to modify the surface of the asymmetric membrane. The hydrophobic initiator adsorbed on the APRO membrane was used to initiate the water-soluble monomer in aqueous phase. The APRO membrane was immerged into ether solution of benzoyl peroxide (BPO). The BPO was physically adsorbed onto the membrane surface. The hydrophobic initiator was inhibited to diffuse through membrane surface into the aqueous solution of the acrylic acid monomer because of a hydrophilic/hydrophobic barrier. The grafting process was triggered by the residing BPO on the membrane surface in an aqueous medium at 70°C for a certain time interval. The surface changes of grafted membrane were characterized with ATR-FTIR, SEM, AFM and contact angle measurements. The results showed the PAA is successfully grafted on the APRO membrane surface. When the grafting rate of PAA was increased from 0% to 8.02%, the edge of leaf-like surface of APRO membrane was gradually curled and the roughness of APRO membrane was decreased about 36% (Ra). These changes of membrane surface increased the hydrophilicity of the APRO membrane surface and the contact angle decreased by about 50%.