Drying stresses to tune strength and long-range order in nanocellulosic materials

A vast range of extraction processes, chemistries, and wet processing methods have been explored to improve the opto-mechanical properties of nanocellulosic materials. However, the stresses that arise during drying have been scarcely examined, in particular for their impact on performance. As with papermaking, drying is a critical step that significantly impacts the properties of nanocellulosic materials. The nano- and micro-scaled dimensions of nanocelluloses provide opportunities beyond those achievable in paper science, as the associated drying stresses are several orders of magnitude higher than those at the macroscale. Drying may be utilized towards the generation of assemblies with functional structures and enhanced properties. Herein, we highlight recent examples where such drying stresses are tethered to the structure of nanocellulosic materials. Using cellulose nanocrystals (CNCs), we investigate how the stresses that develop upon consolidation, and that remain thereafter (i.e., residual stresses), correlate with the mechanical performance of the obtained materials. We extend this analysis through results that highlight the impact of the “history” of drying of CNCs on the dynamics of the residual stresses. We also briefly discuss how inhomogeneous concentration gradients in drying suspensions may play an important role in the formation of superstructures across a range of nanocellulosic materials. Overall, by highlighting the importance of drying, we expect a more closely scrutinized science of drying to improve the properties of  structures based on nanocellulose.