Cellulose nanofibril films as templates for functional membranes

Renewable and sustainable membrane systems are required in technological fields ranging from water purification to biosensors and analytics. Tunable membrane materials are demanded for such systems, as each application entails its own characteristic performance requirements. Wood-based cellulose nanofibrils are intriguing building blocks for such materials due to their large surface area, strong film-forming tendency and numerous reactive groups. Reactive groups on fibril and film surfaces can be used for customizing mechanical and surface characteristics of the membrane material by chemical modification, enabling their utilization as for example organic solvent nanofilters and ion capturing materials. In this work, TEMPO oxidized cellulosic nanofibrils were covalently bonded with poly(vinyl alcohol) to render water stable films with adjustable mechanical properties. Stimuli-responsive poly(N-isopropylacrylamide) was grafted in order to control the hydrophilic-hydrophobic balance and adhesion properties of the membrane. Film characterization performed using surface sensitive methods showed that grafting could be carried out effectively as a surface reaction, without affecting the morphological features of the film. The nanocellulosic film developed here offers a template for diverse chemical modifications and can be tailored to meet the requirements of membrane applications.