Thermo-responsive nanofibrous composite membranes for efficient self-cleaning of protein foulants

This study developed a self-clean thermo-responsive nanofibrous poly(vinylidene fluoride) (PVDF)/nylon-6,6/poly(N-isopropylacrylamide) (PNIPAAm) composite ultrafiltration membrane consisting of a nylon-6,6/PNIPAAm functional nanofibre layer integrated into a PVDF substrate. The morphological analysis showed the presence of electrospun nano-nets branching out from the main nanofibres as PNIPAAm concentration increased, affecting the pore size distribution and solute rejection. The PVDF/nylon-6,6/PNIPAAm membranes showed improved surface hydrophilicity below the low critical solution temperature (LCST) and strong thermo-switchability. With bovine serum albumin (BSA) as the model foulant, the rejection of the 4 wt% PNIPAAm membranes was greatly improved to above 96%. Through a two-cycle ultrafiltration study using feed solution containing BSA and CaCl2, the membrane with 4 wt% PNIPAAm showed superior recovery of water permeance up to 97% assisted with temperature-change cleaning, compared to the control membrane that only recovered 56%. Filtration experiments with and without intermediate temperature-change cleaning proved that the antifouling mechanism of the PNIPAAm membranes was strongly associated with surface wettability and rapid conformation of PNIPAAm polymer chains induced by volume-phase transition, resulting in reduced protein adsorption and 'shaking-off' of the absorbed proteins from the membrane surface. Such smart responsive membranes have great potential for the development of easy-to-clean membranes for food and wastewater treatment.