In this article, the low-field nuclear magnetic resonance was used to measure the moisture content (MC) and MC profiles in poplar wood during real-time drying. The T₂ distribution curve at each drying stage measured using the Carr–Purcell–Meiboom–Gill pulse sequence provided detailed information in the dynamic change of free water as well as bound water of the whole wood sample. In addition, a new developed SE-SPI pulse sequence was first used to evaluate the spatially resolved T₂ distribution of the successive nondestructive sliced layer of wood. Combined with the area integration method, the moisture content in each layer was calculated, and the change of MC profiles within wood at the MC above and below fiber saturation point was well reflected.

The shrinking and swelling of wood due to moisture changes are intrinsic material properties that control and limit the use of wood in many applications. Herein, hygroscopic deformations of normal and compression wood of Chinese fir (Cunninghamia lanceolata[Lamb.] Hook.) were measured during desorption and absorption processes. The dimensional changes were observed in situ by an environmental scanning electron microscope and analyzed at different hierarchical levels (tissue, cell and cell wall). The relationship between moisture variation and hygroscopic deformation was measured. During initial desorption periods from 95 to 90 or 75% RH, an expansion of the lumen and a shrinkage of the cell wall were observed, revealing a non-uniform and directional deformation of single wood cells. The variation of shrinking or swelling at different hierarchical levels (tissue, cell and cell wall) indicates that the hygroscopic middle lamella plays a role in the deformation at the tissue level. Higher microfibril angles and helical cavities on the cell wall in compression wood correlate with a lower shrinking/swelling ratio. Normal wood showed a more pronounced swelling hysteresis than compression wood, while the sorption hysteresis was almost the same for both wood types. This finding is helpful to elucidate effects of micro- and ultrastructure on sorption. The present findings suggest that the sophisticated system of wood has the abilities to adjust the hygroscopic deformations by fine-tuning its hierarchical structures.

The effects of time and temperature on dynamic viscoelastic properties of Chinese fir (Cunninghamia lanceolata [Lamb.] Hook) were investigated using dynamic mechanical analysis in this study. The isothermal tests were applied to the small clear specimens with a moisture content of about 0.6% at constant temperatures ranging from 25 to 200°C for 550 min at atmospheric pressure. Changes in storage modulus and loss tangent with heating time were examined. The results indicated that heating time mainly resulted in thermal softening, thermal degradation of wood, and the reduction of wood stiffness. At more than 60°C, the reduction in storage modulus was accelerated generally as the wood was subjected to a higher temperature or longer heating time. At constant temperatures of 140 and 160°C, a relaxation phenomenon was observed with a slight change in weight, which could be attributed to the relocation of lignin molecules. At the temperature range of 140 to 180°C, the higher the heating temperatures, the earlier the tanδ peak appeared. It is suggested that the wood thermal softening occurs at higher temperatures with shorter heating times or at lower temperatures with longer heating times. At temperatures of 180 and 200°C, the loss of amorphous polysaccharides due to thermal degradation is considered to be the main factor affecting wood viscoelasticity.