Despite the structural, load-bearing role of cellulose in the plant kingdom, countless efforts have been devoted to degrading this recalcitrant polysaccharide, particularly in the context of biofuels and renewable nanomaterials. Herein, we show how the exposure of plant-based fibers to HCl vapor results in rapid degradation with simultaneous crystallization. Because of the unchanged sample texture and the lack of mass transfer out of the substrate in the gas/solid system, the changes in the crystallinity could be reliably monitored. Furthermore, we describe the preparation of cellulose nanocrystals in high yields and with minimal water consumption. The study serves as a starting point for the solid-state tuning of the supramolecular properties of morphologically heterogeneous biological materials.

Swelling behavior and rearrangements of an amorphous ultrathin cellulose film (20 nm thickness) exposed to water and subsequently dried were investigated with grazing incidence X-ray diffraction, neutron reflectivity, atomic force microscopy, and surface energy calculations obtained from contact angle measurements. The film swelled excessively in water, doubling its thickness, but shrunk back to the original thickness upon water removal. Crystallinity (or amorphousness) and morphology remained relatively unchanged after the wetting/drying cycle, but surface free energy increased considerably (ca. 15%) due to an increase in its polar component, that is, the hydrophilicity of the film, indicating that rearrangements occurred during the film's exposure to water. Furthermore, stability of the films in aqueous NaOH solution was investigated with quartz crystal microbalance with dissipation monitoring. The films were stable at 0.0001 M NaOH but already 0.001 M NaOH partially dissolved the film. The surprising susceptibility to dissolve in dilute NaOH was hypothetically attributed to the lack of hierarchical morphology in the amorphous film.

Small-angle scattering methods allow an efficient characterization of the hierarchical structure of wood and other cellulosic materials. However, their full utilization would require an analytical model to fit the experimental data. This contribution presents a small-angle scattering model tailored to the analysis of wood samples. The model is based on infinitely long cylinders packed in a hexagonal array with paracrystalline distortion, adapted to the particular purpose of modelling the packing of cellulose microfibrils in the secondary cell wall of wood. The new model has been validated with small-angle neutron and X-ray scattering data from real wood samples at various moisture contents. The model yields reasonable numerical values for the microfibril diameter (2.1–2.5 nm) and packing distance (4 and 3 nm in wet and dry states, respectively) and comparable results between the two methods. It is particularly applicable to wet wood samples and allows changes in the packing of cellulose microfibrils to be followed as a function of moisture content.