Polyacrylic desalination membranes. I. Synthesis and characterization

Abstract

AbstractA new class of desalination membranes has been developed. The membranes were prepared by polymerizing mixtures of two hydrophilic monomers (N‐methyloacrylamide and acrylic acid), a hydrophobic monomer (ethyl acrylate) and a hydrophobic crosslinking monomer (trimethylol propane trimethacrylate) followed by heat treatment. The membranes were homogeneous, averaging about 6 mils in thickness. They were characterized by measuring water contents and salt distribution coefficients using an immersion technique. The fractional water contents in the membranes varied between 0.16 and 0.44 as the molal salt distribution coefficients increased from ca. 0.22 to 0.43. Increasing contents of the hydrophobic monomer and/or crosslinking monomer led to decreased water and salt contents, as expected. A model is postulated in which the water is assumed to be distributed within the polymer in two forms: (1) as primary water, hydrogen‐bonded with hydrophilic polymer groups, and (2) secondary water, imbibed with salt from the external solution into hydrophilic regions or defects within the polymer matrix. It was found that primary water content was approximately constant for all compositions and varied between ca. 2–3 moles of primary water/mole of hydrophilic monomer in the membrane.