Wood's moisture response varies by type, offering clues for material engineering
Scientists using computer simulations discovered that compression wood and opposite wood—two types that grow in tree branches—absorb water differently due to subtle chemical variations in their lignin structure. The finding could help engineers design more durable wood products and improve performance in humid environments.
Originaltitel: Lignin Hygroexpansion in Compression and Opposite Wood: a Molecular Dynamics study
<p>Softwood branches develop compression wood (CW) in the lower parts of thebranch, while opposite wood (OW) develops on the upper. These wood typesdiffer in structure at several length scales, among others in the chemical composition of their lignin matrix. While OW mostly contains guaiacyl (G) units, CW is known to contain a substantial fraction of 4-hydroxyphenyl (H) lignin.In this study, the impact this difference has on lignin hygroexpansion and inter-action with water is studied by the means of atomistic models and moleculardynamics computer simulations of lignin systems at different levels of hydration. It was found that, despite the minor difference in chemical composition, thereare differences in swelling, structure and water dynamics. CW lignin is found tohave a higher uniaxial swelling coefficient, since the phase separation between lignin and water is more pronounced. This behavior is linked to structural differ-ences, where intermolecular π−π stacking is more common in CW lignin andhydrogen bonding to water more pronounced in OW lignin. These findings are of interest for understanding the role of lignin in CW, and general understanding of moisture interaction with lignin inside wood cell walls.</p>