Preparation and properties of grafted membranes for desalination. Part I

Abstract

AbstractStyrene grafting to cellulose acetate has been studied in an attempt to synthesize a cellulose acetate reverse osmosis membrane with improved resistance to compaction. The studies reported here involved grafting to homogeneous cellulose acetateE‐398‐3 Eastman Chemical Company. film and evaluation of the tensile creep and water sorption behavior of the resulting grafts. The grafting studies involving homogeneous cellulose acetate films indicated that the kinetics of grafting were rate controlled by monomer diffusion to the growth site. By controlling the ratio of styrene to pyridine (monomer/swelling agent) and controlling total dose, reproducible and predictable grafts were prepared. The tensile creep rate of wet cellulose acetate–styrene grafts decreases sharply with increasing styrene content up to 40% styrene and then decreases more slowly as styrene content is further increased. The creep rate of grafts containing 40% styrene is 7.5 times lower than that of ungrafted cellulose acetate. Unsteady‐state water vapor sorption experiments revealed that the equilibrium water content was decreased as a consequence of grafting although water diffusivities were increased or decreased as percent graft was increased according to the method and level of grafting. Water sorption deviated slightly from Henry's law behavior. The water diffusivity, as measured by the rate of sorption, was concentration dependent, decreasing with increasing water concentration. Membrane constants for water transport (defined as D 1C1 g‐cm/cm2‐sec) could be increased or decreased as a consequence of grafting.