Hygroscopic properties of PEG treated archaeological wood from the rampart of the 10th century stronghold as exposed in the Archaeological Reserve Genius loci in Poznań (Poland)

The archaeological wood from the rampart of the Poznań stronghold built in the 10th century was subjected to the investigations. The material was obtained during the excavations and conservation works of the earthen and wooden relicts. The archaeological wood, both untreated and treated with polyethylene glycol (PEG), was characterized by determining adsorption and desorption isotherms, which were formed by GAB and GDW models. The anomalous increase of the equilibrium moisture content for air relative humidity values above 80% was found for the PEG treated wood. It was clearly presented that the safety of wood exposition strongly depends on the proper maintaining of air parameters. The mechanisms of the reduction of equilibrium moisture content and sorption hysteresis for the PEG treated wood were explained. It was not recommended to predict equilibrium moisture content values with the Hailwood-Horrobin model fitted to the sorption data collected by the US Forest Products Laboratory as it was not accounting for sorption hysteresis, decay of archaeological wood and the influence of the PEG treatment.