Diffusion of chemicals into archaeological waterlogged hardwoods obtained from the Thang Long Imperial Citadel site, Vietnam

Abstract

This study shows a method to easily develop suitable impregnation procedure of chemicals for preserving the archaeological waterlogged wood (WW) using diffusion constant. The steady-state diffusion coefficients of polyethylene glycol 4000 (PEG4000), trehalose, and keratin through eight archaeological waterlogged wood species were obtained from the total amounts of the chemicals diffused through the wood samples. The diffusion coefficients were strongly affected by the anatomical structures of the wood species and degree of wood deterioration. Within the same species of wood, the highest diffusion rates were measured in the longitudinal direction, followed by those in the radial and tangential directions. The longitudinal diffusion coefficients were 1.5-to 8.1-times higher than the radial diffusion coefficients, which were in turn approximately 1.1-to 5.7-times higher than the tangential diffusion coefficients. The diffusion rates were found to be inversely proportional to the molecular weight of the diffusing chemical. The diffusivity of trehalose through the waterlogged woods was found to be higher than those of keratin and PEG4000. This study provides a potential method to easily estimate chemical diffusion coefficients for dip-diffusion treatments.

Conservation of Waterlogged Wood—Past, Present and Future Perspectives

“…PEG was first used in the preservation of wooden artefacts after research at the Forest Products Laboratory in Madison WI in the 1950s [107][108][109][110]. The diffusion of PEG into waterlogged wood is a slow process, which is influenced by the MW and composition of the consolidant, the orientation of the wood sample with respect to the diffusant, anatomical characteristics of the wood and extent of deterioration of the wood, as well as physical conditions, such as the temperature of treatment [111]. Heavily degraded wood with a low density will exhibit severe collapse on drying and is usually treated with high MW PEG, followed by freeze-drying.…”