Mechanical properties of asymmetric polysulfone membranes containing surfactant as additives

The mechanical properties of surfactant containing asymmetric polysulfone ( PSf) membranes were under investigation. The investigated mechanical proper ties include the tensile strength at break, the elongation at break, and th e initial Young's modulus. Lipophilic surfactant (Span-80) or hydrophilic s urfactant (Tween-20) was added in the PSf casting solution. The effects of surfactant concentration and casting temperature on the mechanical properti es of resulting membranes were measured and compared. Experimental results showed that all of the three mechanical properties increased with an increa se of the Span-80 content. However, when the surfactant additive was substi tuted by the hydrophilic Tween-20, the tensile strength at break and the in itial Young's modulus decreased with an increase of the surfactant content, despite the increase of the elongation at break. The plasticizing effect m ight be the major contribution of surfactant Tween-20 on the membrane's mec hanical strength, but surfactant Span-80 affected the membrane's mechanical strength mostly through alteration of the membrane structure. The addition of Span-80 resulted in the suppression of macrovoids and formation of a th icker skin layer and a denser membrane structure. Therefore, as Span-80 was added in the casting solution, the consolidated membrane structure resulte d in an increase in all of the three measured mechanical properties. The ab ove results indicate that we ought to know the effect of surfactants on the membrane structure in order to evaluate how the addition of surfactants af fects the mechanical properties of an asymmetric membrane made by the wet i nversion method.