Performance of polyacrylamide and poly(acrylamide/sodium acrylate) hydrogel-coated mesh for separation of oil/water mixtures

Hydrogels are widely used as a coagulant in water treatment in addition to using in tissue engineering due to their high water absorption capacity and biocompatibility. Our research objective is to synthesize a reinforced membrane made using hydrogels targeted for the separation of water from oil-water mixtures. The reinforced hydrogel is synthesized by graft polymerization of water-soluble polymer such as polyacrylamide (PAM) homo-polymer and poly (Na-Ac/AM) copolymer reinforcing on a thin-fine metallic mesh. Different factors such as the mesh size, the percentage of coated-hydrogel, swelling index are varied to study their effect on the separation efficiency. The morphology of the reinforced hydrogel was analyzed by using scanning electron microscopy. In the case of hydrogels made from copolymers, the effect of the corresponding concentration of the copolymer on the separation efficiency is studied. Oil-water mixtures of 5/95 and 10/90 oil/water % were chosen based on typical compostion found in industrial wastewater. The wettability of water and oil on the PAM- hydrogel coated mesh was evaluated using the contact angle measurements obtained at ambient temperature. It was found that PAM polymer and Na-Ac/AM copolymer hydrogel coated meshes are super-hydrophilic in an air-solid-liquid three phases with both contact angles in oil and water less than 15°. Underwater contact angles for the four different sizes of meshes based on PAM coated mesh are observed to be greater than 90°. This indicates the oleophobic properties of the coated mesh under the water and oil cannot penetrate through the coated mesh while the water alone is absorbed through it. The difference in the water flow or separation time becomes smaller with increasing the mesh’s pore size up to 80 μm, while separation time was higher for 200 μm mesh as more hydrogel was blocking the pores. In contrast, the separation time is faster with the copolymer due to the higher swelling capacity of the copolymer. Therefore, under-water oleo-phobic properties of the PAM coated meshes make it a promising candidate for separation of oil/water emulsions with more than 95% separation efficiency.