Abstract
The current work aims at the study of the biological degradation of archaeological European white elm via microscopy and chemical analysis in order to identify the kind of biological degradation and characterize the state of preservation of this type of wood. Profound knowledge of the chemical constituents and biological degradation in fresh-cut and archaeological elm wood will simplify the process of restoration and conservation of the investigated artifacts. Therefore, fresh-cut and archaeological elm were compared in terms of extractive, chlorite holocellulose, α-cellulose, lignin, and ash contents. In the fresh-cut elm wood, the contents of Kürschner–Hoffer cellulose, chlorite holocellulose, α-cellulose, and hemicellulose were significantly higher than that of the archaeological elm, confirmed by the degradation of native wood hemicelluloses by erosion bacteria during soil contact. Naturally, the mass percentage of lignin increases as the amount of chlorite holocellulose in the wood decreases. These wet chemistry results were also confirmed by FTIR analysis, where bands mainly attributed to hemicellulose and cellulose decreased significantly and bands belonging to lignin display higher intensity for the archaeological specimens. Ash and cyclohexane–ethanol extract contents of archaeological elm wood were significantly higher due to the movement of mineral components arising out of the soil into the wood specimens. Based on the microscopic investigation and given the fact that wood decay fungi need oxygen to degrade wood and the investigated archaeological elm specimens were buried to a 10 m depth in the soil, we might conclude that the wood degradation was caused by erosion bacteria.
Highlights
Wood is a naturally robust material long known for its flexible and attractive structural properties and engineering
Current research study on fresh-cut and historic elm (Ulmus spp.) shows that the contents of Kürschner–Hoffer cellulose, chlorite holocellulose assays/α-cellulose, and hemicellulose in the fresh-cut wood were significantly higher than that of the archaeological one, which was explained by the degradation of native wood hemicelluloses during soil contact by erosion bacteria and most likely in the low oxygen amount
The following bands, 1121, 1051, 1028 cm−1, mainly attributable to CO vibrations in hemicelluloses, decrease significantly for the archaeological elm specimen and between 1645 and 1237 cm−1 adsorbed OH bands, β-glucosidic bonds or conjugated C = O groups display high intensity for the archaeological specimen, according to the ATR FTIR spectrum. Such results indicate that cellulose and hemicellulose are the main elements to be degraded during storage completely buried and that the percentage amount of lignin increases with their degradation
Summary
Wood is a naturally robust material long known for its flexible and attractive structural properties and engineering. There are many aggressive wood-destroying fungi, such as white and brown rot fungi Such basidiomycetes specialize in colonizing wood and extensively degrading lignocellulosic materials under certain conditions of the environment and the substrates. Most terrestrial ecosystems usually have their optimum conditions [4] Another group of fungi that includes ascomycetes and deuteromycetes species are capable of attacking wood exposed in the soil in very high moisture contents, as well as in fresh and saltwater. These soft rot fungi are considered to have a lower oxygen demand than basidiomycetes [3]. Humid conditions and air contact are essential for all wood-destroying fungi since the fungal enzyme system uses oxygen as an electron acceptor in the process of decomposing the complex wood structure
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