Impact of Drying on Wood Ultrastructure: Similarities in Cell Wall Alteration between Native Wood and Isolated Wood-Based Fibers

Ultrastructural alterations of fresh wood caused by initial drying were compared to changes incurred during drying of never-dried wood pulp fibers of different macromolecular composition. Drying induced inaccessibility of a native wood sample exhibited remarkable similarity to wood pulp samples of different lignin contents. The results suggest that the supramolccular rearrangements in native wood matrix upon dehydration are qualitatively identical to the well-known changes occurring in pulp fibers after drying, although the changes are considerably different in quantity. The alterations were observed and quantified by monitoring the conversion of accessible deuterium exchanged OH groups in fresh wood and wood pulp fibers to inaccessible, reprotonation resistant OD groups during drying. The deuteration/FT-IR measurements correlated well with the water retention measurement of the pulp samples. Irreversible reduction of water retention due to the supramolecular changes implies reduced accessibility of wood polymers in various chemical and mechanical treatments, such as enzymatic conversion of biomass or preparation of cellulosic nano-objects for diverse applications.