Thermo-responsive mixed-matrix hollow fiber membranes

Up to date, preparation of thermo-responsive mixed-matrix membranes (MMM) has only be described as small scale flat membranes or multi-step processes for hollow fiber membranes. In this work, the development of thermoresponsive MMM hollow fibers composed of polyethersulfone as membrane polymer and poly(N-isopropylacrylamide) (PNIPAM) microgel particles via the wet spinning process is presented. PNIPAM particles are synthesized with (NP-S, zavg 20°C = 105 nm) and without (NP-L, zavg 20°C = 250 nm) sodium dodecyl sulfate and their thermo-responsive behavior is characterized by dynamic light scattering. Particle size (NP-S, NP-L), particle content (10%, 15%) and the extrusion pressure in the wet spinning process (1.0-3.0 bar) are investigated as experimental parameters. Reversible thermo-responsive behavior of the hollow fibers is demonstrated by water permeability measurements at different temperatures (20 and 50°C). The largest switching factors (R) are observed for the hollow fibers containing NP-L. For 15% NP-L and 1 bar extrusion pressure, water permeances between 0.5 and 6.0 L m−2 h−1 bar−1 are observed, corresponding to R = 12 and a dextran (500 kDa) rejection of 91% at 25°C.