Miscibility and Hydrophobicity of Pyrrolidone-Containing Copolymers Determine Blend Membrane Properties for Diffusion Dialysis

Dense polymeric blends with (transiently) fixed positive charges are ideal as anion exchange membranes (AEMs) for treating acidic wastewater with salts via diffusion dialysis. Pyrrolidone from vinylpyrrolidone (VP) copolymers offers a unique chemistry compared to conventional quaternary ammonium, enabling greener and more efficient membrane synthesis. The hydrophobic/hydrophilic characteristics and the miscibility of copolymers with membrane materials determine the microstructure and consequent membrane properties. Here, a commercial copolymer, poly(vinylpyrrolidone-co-vinyl acetate) (P(VP-VAc)), was blended with membrane material polyether sulfone (PES) to prepare PES-P(VP-VAc) blend membranes. The influence of VP content in the copolymers, casting solution composition, and membrane microstructure on the physicochemical properties, mass transfer performance, and stability of the membranes was systematically investigated. It was found that the copolymers (63.8–73.2 wt % VP content, ∼80 kDa) were partially miscible with PES, resulting in microphase-separated membranes. With the VP mass fraction in the blend membranes increased, both the membrane mass increase and volume swelling degree in water and acid increased. When the membrane VP mass fraction reached 41.5 wt %, the permeability coefficients of sulfuric acid and ferrous sulfate increased rapidly. The PES-P(VP-VAc 6/4) blend membrane, containing 41.5 wt % VP, exhibited sulfuric acid and ferrous sulfate permeability coefficients of 228.5 and 4.1 × 10–9 m2/h, respectively. By simply blending two commercial polymers, this study successfully prepared PES-P(VP-VAc) blend AEMs with a microphase-separated structure, and their application in sulfuric acid recovery through diffusion dialysis was evaluated.