Nanocellulose is an excellent candidate to replace traditionally fossil-derived materials. Although several cellulose nanomaterials (CNM) have reached the commercial market, the full potential of nanocellulose has yet to be realized. For the continued development of CNM for realistic applications, a deeper understanding on the influence of moisture on the structure and dynamics of these hygroscopic materials is needed. In this thesis, a combination of neutron and X-ray scattering has been deployed to evaluate the moisture-induced structural and dynamical alterations of CNM.

Inelastic neutron scattering (INS) was used to access the full vibrational spectra of nanocellulose with three different crystallinities, revealing that moisture primarily interacts with the disordered regions of the cellulose chains. A combination of INS, small angle neutron scattering, and wide angle X-ray scattering (WAXS) was used to link moisture-induced structural modifications in anisotropic cellulose nanocrystals (CNC) foams to the population change in the phonon density of states; an increasing separation distance between nanoparticles was suggested to suppress the effect of higher crystallinity index and larger coherence length.

The hydration-dependent dynamics and temperature-dependent water diffusion in nanocellulose were investigated using quasielastic neutron scattering. A localized rotational motion of the C6 hydrogens could be detected, and hydration was found to result in an increased cellulose chain mobility. At 270 K, water was found to diffuse independently of cellulose, with the extracted diffusion coefficient matching that of bulk water. At 310 K, the diffusion coefficient was lower than that of bulk water. This could be attributed to water diffusing on the surface of CNC, where the water-cellulose interactions may slow the diffusion.

Anisotropic cellulose nanofibril (CNF) foams obtained from upcycled cotton waste textiles (upCNF) and softwood (wCNF) were subjected to a relative humidity range of 10 and 90% and their structural humidity-response evaluated using in-situ small angle X-ray scattering (SAXS), WAXS, and X-ray microtomography. Across the investigated length scales, the upCNF foams exhibited a superior integrity compared to the wCNF foams, highlighting the potential of cotton waste textiles as a source of nanocellulose.

Multidirectional neutron dark-field tomography (MD-NDFT) has been demonstrated as a non-destructive and non-invasive method for advanced characterization of hierarchical materials. This was achieved by using the simple hierarchical structure of anisotropic CNC and CNF foams as model systems, where the alignment of nanoparticles in the full foams was revealed by MD-NDFT and cross-validated with SAXS on the nanometer scale. The dactyl club of the mantis shrimp was also measured, highlighting the potential of MD-NDFT for nature’s more complex hierarchical constructs.