Evaluation of the average state of carbohydrate/lignin coexistence in wood by analysis of molecular motion

To estimate the effect of chemical treatment of wood or typify the phenotypes of genetically modified plants, it is necessary to know the coexistence mode of wood components. Herein, the average states of carbohydrate/lignin coexistence in ball-milled and cellulase-treated wood powder samples were investigated using molecular motion evaluation methods, which were originally established for phase structure analysis of simple, miscible polymer blends. Our aim was to depict the nanoscopic arrangements of the major components of wood using a unified approach. The targeted scales were 20–30 nm, which was evaluated using glass transition temperatures measured by differential scanning calorimetry, and approximately 2 nm, which was evaluated using spin–lattice relaxation times of the 1 H nucleus ( T 1 ρ H ) in a rotating system measured by solid-state nuclear magnetic resonance spectroscopy. In both softwood (Japanese cypress, Chamaecyparis obtuse ) and hardwood (eucalyptus, mainly Eucalyptus globulus ) samples, the main components coexisted in the range 20–30 nm. The T 1 ρ H data revealed that the carbohydrates and lignin behaved independently in wood powders after pulverization, but their molecular motions became similar after enzymatic hydrolysis of cellulose. This meant that hemicellulose and lignin were within approximately 2 nm of each other. The results are consistent with the major findings from microscopy, thermal analysis, spectroscopy, and quartz crystal microbalance measurements. Limitations on the application of these numerical assessments were considered. We envisage that molecular motion data could be applied as an index to connect the wood composition with properties related to wood utilization. Graphic abstract