Chemical characterization of archaeological marine wooden piles from the ancient harbor Theodosius in Istanbul

Abstract

The ultrastructure and chemical composition of marine wooden piles from Cupressus sempervirens and Castanea sativa, buried for approximately 1000 years, were investigated along with recent woods (RW) using wet chemical analyses, FTIR spectroscopy, and TGA. The ash content in RW chestnut samples was 0.49%, compared to 3.30% in archeological wood (AW), and for cypress, it was 0.32% and 1.87%, respectively. Solubility in ethanol–cyclohexane decreased in the archaeological samples due to extractives leaching, while cypress AW showed increased solubility at 1% NaOH. Differences in polysaccharide degradation ratios during aging were observed, with cypress wood having lower ?-cellulose content than chestnut wood. Glucuronoxylans in hardwood degraded easily, while galactoglucomannan in cypress exhibited more resistance. Lignin showed two types of alteration, with slight increase in hardwood and higher values in softwood due to reduced holocellulose. Micro and morphological changes were identified using light microscopy and SEM. Inorganic material accumulation was observed in AW, while resin residues were found only in cypress wood. Cell wall delamination, degradation in ray cells, and deposits from inorganic matter or fungal hyphae were observed. EDX analysis revealed lower potassium contents in AW samples compared to petrified wood. Iron was detected in archaeological chestnut wood, attributed to tannin content acting as a chelator. Chestnut AW exhibited high calcium content due to calcification. FTIR spectra showed minimal hemicellulose peaks in archaeological samples, consistent with wet analysis. The disappearance of the shoulder below 300 °C in the DTG curve indicated hemicellulose loss, especially in AW chestnut. Lignin index values correlated with wet analysis, with higher values in cypress AW. The intensity of lignin-associated peaks at 1510 cm?1 was higher in archaeological samples. The second peak in the DTG curve, related to lignin and phenolic compound degradation, was observed at lower temperatures, particularly in chestnut AW. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.