Recent advances and an industrial perspective of cellulose nanocrystal functionalization through polymer grafting

Cellulose nanocrystals (CNCs) are an emerging nanomaterial for applications ranging from coatings and construction to adhesives and biomedical devices. Owing to their high aspect ratio, stiffness, and reinforcing potential, CNCs have shown great promise to be used in polymer nanocomposites. However, due to their inherent hydrophilicity and compatibility with polar environments, the use of CNCs in hydrophobic polymer matrices or in organic solvent-based formulations has been limited. To overcome this incompatibility, many reports on grafting polymers onto the surface of CNCs have been published over the past ten years. This review describes the recent advances in CNC surface functionalization through polymer grafting, and comprehensively covers the existing work to date. Methods including polymer grafting to and grafting from are described in detail, using polymerization techniques such as free radical, ring opening, and controlled radical polymerization. Purification and characterization of polymer-grafted CNCs, the potential for upscaling these functionalization methods, and current perspectives from academic and industrial viewpoints are presented.