Stimuli response polypropylene membranes as selective separators for alkaline ions

Poly(N‐isopropylacrylamide), copolymer of poly(N-isopropylacrylamide)-co-di(ethylene glycol)methyl ether methacrylate, poly(acrylic acid) or copolymer of poly(acrylic acid-co-di(ethylene glycol)methyl ether methacrylate) was grafted to polypropylene membranes by means of plasma treatment. Dielectric plasma discharge reactor was applied for membrane activation. The grafted polymers exhibited excellent conformational responses to temperature or to pH. The prepared membranes were impermeable to water at room temperature and at pH below 4.5, while at 43 °C and pH above 4.5 the volumetric flux reached 30 L/m2 h at 0.05 MPa. Permeation of KCl, NaCl and LiCl was tested in a process of direct dialysis. The best fluxes of KCl, NaCl and LiCl were obtained at room temperature and at pH below 4.5. It was shown that DEGMEM blocks were able to participate in transport of potassium, sodium and lithium ions and membranes with these blocks were more selective to Li than to other ions.

► pH and temperature dependent membrane permeability.
► Facilitated transport of Li ions through membranes grafted with copolymers of PNIPAM–DEGMEM and PAA–DEGMEM.
► Formation of transport channels induced by temperature or pH change.