The cellular components of historical or archaeological wooden objects can be degraded by fungi or bacteria during ageing. However, understanding the chemical changes of the molecular and structural features of lignin during ageing and degradation remains inadequate. To improve the state of knowledge in this field of study, lignins from archaeological fir wood aged in tombs, which range in years from ∼200 BC–1600 AD, have been thoroughly analyzed. Results from the visual fluorescence images showed that the lignin in certain regions of the xylem cell wall underwent more degradation compared to the control sample (healthy fir wood). Chemical analysis and structural analysis, using nuclear magnetic resonance, of isolated lignins from each wood sample indicated lignin depolymerization via loss of native substructures, most notably a decrease in β-O-4 linkages over time. Relative to the control sample, it is found that ageing mostly induces depolymerization, but certain results hint that lignin repolymerization might take place at extended ageing times. Overall, the results obtained can help guide efforts towards taking better care of archaeological woods uncovered across the world.

An image dataset of the cross-sectional optical micrographs of the Lauraceae species including 39 species in 11 genera, capturing at least one full annual ring, was investigated by scale-invariant feature transform (SIFT), a computer vision-based feature extraction algorithm. We found an image of 900 × 900-pixel size at a pixel resolution of ca. 3 µm, corresponding to the actual size of 2.65 × 2.65 mm², as the minimum requirement for the image dataset in terms of the accuracy of the recognition at both the genus and species levels. Among the several classifiers investigated, the linear discriminant analysis (LDA) presented the best performance reaching a maximum of 89.4% in the genus with a species identification of approximately 96.3%. Cluster analysis of all the SIFT descriptors for each image yielded practical information regarding the descriptors; they recognize selectively the cell lumina, cell corners, vessels, and axial and ray parenchyma cells. Therefore, the difference between the genus or species levels was determined per the variation in the quantities of these computer-based properties. Another clustering approach, the hierarchal dendrogram, was applied to visualize the numerical distances between the genus and species. Interestingly, even Machilus and Phoebe, which are difficult to distinguish by conventional visual inspection, are quite distantly classified at the genus level. In contrast, some species in Cinnamomum, Machilus and Litsea were categorized into different subgroups rather than the original genus. Microscopic wood identification is found to be possible at the genus level; however, the numerical dataset of the morphological features has various overlapping clusters, causing the genus-level identification of the Lauraceae to be more difficult than species-level identification.

The fiber bundles from the lignified leaf sheath of windmill palm (Trachycarpus fortunei) are widely used as natural fibers for various products, and exhibit excellent durability. In this study, the cell wall of windmill palm fibers was characterized using transmission electron microscopy, high resolution field emission scanning electron microscopy, and polarized light microscopy, and chemical analysis to measure lignin content. It was found that (1) the secondary wall was composed of just two layers, outer (equivalent to S1, 0.65 ± 0.12 μm) and inner (equivalent to S2, 1.28 ± 0.30 μm) ones, with a high ratio of S1 to the whole cell wall thickness; (2) the microfibrils of the S1 are orientated in an S-helix (MFA, 127.0° ± 2.0), and those of the S2 in a Z-helix (MFA, 43.7° ± 2.2); and (3) the Klason lignin content of fiber bundles was very high (nearly 40%). It is suggested that these structural and chemical features of windmill palm fibers are involved in their mechanical properties such as high flexibility and elasticity, and also related to their high durability.