Modern technology has enabled the isolation of nanocellulose from plant-based fibers, and the current trend focuses on utilizing nanocellulose in a broad range of sustainable materials applications. Water is generally seen as a detrimental component when in contact with nanocellulose-based materials, just like it is harmful for traditional cellulosic materials such as paper or cardboard. However, water is an integral component in plants, and many applications of nanocellulose already accept the presence of water or make use of it. This review gives a comprehensive account of nanocellulose–water interactions and their repercussions in all key areas of contemporary research: fundamental physical chemistry, chemical modification of nanocellulose, materials applications, and analytical methods to map the water interactions and the effect of water on a nanocellulose matrix.

Phosphorylation of cellulose nanocrystals (CNCs) has remained a marginal activity despite the undisputed application potential in flame-retardant materials, sustainable high-capacity ionexchange materials, or substrates for biomineralization among others. This is largely due to strenuous extraction methods prone to a combination of poor reproducibility, low degrees of substitution, disappointing yields, and impractical reaction sequences. Here, we demonstrate an improved methodology relying on the modification routines for phosphorylated cellulose nanofibers and hydrolysis by gaseous HCl to isolate CNCs. This allows us to overcome the aforementioned shortcomings and to reliably and reproducibly extract phosphorylated CNCs with exceptionally high surface charge (∼2000 mmol/kg) in a straightforward routine that minimizes water consumption and maximizes yields. The CNCs were characterized by NMR, ζpotential, conductometric titration, thermogravimetry, elemental analysis, wide-angle X-ray scattering, transmission electron microscopy, and atomic force microscopy.