Chemical Characterization of Archaeological Wood: Softwood Vasa and Hardwood Riksapplet Case Studies

A sample of hardwood from the Riksapplet shipwreck (Dalaro, 1676) and a softwood sample treated with PEG found near the Vasa warship (Stockholm, 1628) wreck site were chemically characterized. The different fractions (namely extractives, lignin and holocellulose) composing the hardwood and softwood samples were isolated and compared with a sound reference sample of the same genus. Two-dimensional Heteronuclear Single Quantum Coherence, 31Phosphorous NMR and gel permeation chromatography showed no differences between the wood samples recovered from the shipwrecks and the reference samples concerning extractives, lignin and holocellulose. Moreover, innovative analyses by gel permeation chromatography of the entire derivatized wood cell wall material that allows for the detection of all substrate components namely, cellulose, hemicellulose, and lignin, particularly focusing on the presence of lignin-carbohydrate complexes, suggested that the molecular weight distributions of the waterlogged wood samples were comparable with the references confirming a good state of preservation. Maximum water content (MWC %), iron and sulfur content have also been measured and related to the result from chemical characterizations.