Understanding hemicellulose-cellulose interactions in cellulose nanofibril-based composites.

Plant-based polysaccharides (cellulose and hemicellulose) are a very interesting option for the preparation of sustainable composite materials to replace fossil plastics, but the optimum bonding mechanism between the hard and soft components is still not well known. In this work, composite films made of cellulose nanofibrils (CNF) and various modified and unmodified polysaccharides (galactoglucomannan, GGM; hydrolyzed and oxidized guar gum, GGhydHox; and guar gum grafted with polyethylene glycol, GG-g-PEG) were characterized from the nano- to macroscopic level to better understand how the interactions between the composite components at nano/microscale affect macroscopic mechanical properties, like toughness and strength. All the polysaccharides studied adsorbed well on CNF, although with different adsorption rates, as measured by quartz crystal microbalance with dissipation monitoring (QCM-D). Direct surface and friction force experiments using the colloidal probe technique revealed that the adsorbed polysaccharides provided repulsive forces-well described by a polyelectrolyte brush model - and a moderate reduction in friction between cellulose surfaces, which may prevent CNF aggregates during composite formation and, consequently, enhance the strength of dry films. High affinity for cellulose and moderate hydration were found to be important requirements for polysaccharides to improve the mechanical properties of CNF-based composites in wet conditions. The results of this work provide fundamental information on hemicellulose-cellulose interactions and can support the development of polysaccharide-based materials for different packaging and medical applications.