Abstract
• Submicron nanocellulose layers generate highly hydrophilic anti-biofouling membrane surfaces. • Microfiltration membranes were altered to ultrafiltration and nanofiltration membranes. • Membrane roll-to-roll modifications were carried out using industrially relevant unit operations. • Nanocellulose layers displayed both size and charge selective separation mechanism with good mechanical integrity. 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.
Highlights
Aside from being a renewable and bio-based alternative for many synthetic polymer-based materials, colloidal nanocellulose (cellulose nanocrystals (CNC), cellulose nanofibrils (CNF), cellulose microfibrils (CMF)) possesses a unique set of features, such as large surface area, nanoporous/microporous fine structure and intriguing interactions with water such as high hygroscopicity, that sets it apart from many other nanoscale materials with comparable aspect ratios and mechanical performance [1]
It can be concluded that our nanocellulose coated PES membranes represent nano filtration membranes and lower boundary of ultrafiltration membranes with clear anti-biofouling performance directly evidenced via systematic bovine serum albumin (BSA) adsorption investigations
Encouraged by our previous experience related to the utilisation of thin nanocellulose coatings on commercial PES microfiltration membranes to advance the anti-biofouling property [15], we introduce a roll-to-roll membrane modification strategy to produce and tailor anti-biofouling PES membranes with size and charge dependent selectivity using unit operations which are compatible with industrial lines (Fig. 1)
Summary
Aside from being a renewable and bio-based alternative for many synthetic polymer-based materials, colloidal nanocellulose (cellulose nanocrystals (CNC), cellulose nanofibrils (CNF), cellulose microfibrils (CMF)) possesses a unique set of features, such as large surface area, nanoporous/microporous fine structure and intriguing interactions with water such as high hygroscopicity, that sets it apart from many other nanoscale materials with comparable aspect ratios and mechanical performance [1]. Polymeric polyethersulfone (PES) microfiltration (MF) and ultrafil tration (UF) membranes are widely used in e.g. biomedical and life science applications to remove small particles, proteins and microorganisms They exhibit outstanding oxidative and thermal stability and good mechanical properties, they are prone to fouling caused by adsorption of proteins and bacteria [14]. Encouraged by our previous experience related to the utilisation of thin nanocellulose coatings on commercial PES microfiltration membranes to advance the anti-biofouling property [15], we introduce a roll-to-roll membrane modification strategy to produce and tailor anti-biofouling PES membranes with size and charge dependent selectivity using unit operations which are compatible with industrial lines (Fig. 1). Following a different approach in pilot scale, foam coating has been employed to apply a thin layer of CNF on a fibre-based substrate to modify the surface [42]. The in tegral anti-biofouling property of the membrane building blocks was demonstrated by following the model protein (Bovine serum albumin, BSA) adsorption by QCM-D
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