Pilot-scale modification of polyethersulfone membrane with a size and charge selective nanocellulose layer

The utilisation of plant-derived nanoscale cellulosic materials (cellulose nanofibrils, CNF) in tailoring water purification membranes is constantly gaining interest in the context of green-functionalised membrane solutions. However, most of the existing approaches based on renewable and biobased materials suffer from the lack of efficient and scalable processing strategies. Here, we introduce a roll-to-roll membrane modification approach based on thin submicron nanocellulose coatings (400-800 nm) to manufacture anti-biofouling membranes with size and charge dependent selectivity using unit operations compatible with existing industrial lines. We turned a commercial polymeric polyethersulfone (PES) microfiltration membrane into highly hydrophilic and tight membrane structure by applying thin and water-durable cellulose nanofibril layers using cast or spray coating methods. Nanocellulose coated membranes exhibited water permeance values of 80 - 100 LMH/MPa with the highest rejection levels of > 90% for Cytochrome C. Furthermore, the nanocellulose layers were able to withstand relatively high filtration pressure levels of 1 MPa, indicating that the selected procedures to improve mechanical integrity i.e. polyethylene imine-based anchoring and acid induced CNF cross-linking were successful. The coated membranes with the thinnest nanocellulose layer exhibited a molecular weight cut-off (MWCO) of 2 kDa for negatively charged polystyrene sulfonate and 14 kDa for neutral dextrane indicating charge selective behaviour. It can be concluded that our nanocellulose coated PES membranes represent nanofiltration membranes and lower boundary of ultrafiltration membranes with clear anti-biofouling performance directly evidenced via systematic bovine serum albumin (BSA) adsorption investigations. Our approach paves the way towards tunable and sustainable water treatment technologies simultaneously opening space for novel biobased solutions in membrane sector.