Dimensional stability and hygroscopic properties of PEG treated irregularly degraded waterlogged Scots pine wood

The study concerns the conservation problem of large scale elements of irregularly degraded archaeological wood being characterized by different susceptibility to agents responsible for wood consolidation and bulking. The conservation effectiveness was established for processes carried out with PEG solutions of different molecular weight with respect to dimensional stabilization, hygroscopic properties and the agent consumption. One of the investigated treatment options had concerned the application of PEG 2000, i.e. poorly studied variant of that type of consolidants. The analysis was performed for wooden elements from a Late Medieval road. The investigated artifacts were characterized by different anatomical structure and each of them included sapwood (SW) and heartwood (HW). Chemical, physical and sorption properties of SW and HW were first determined. A significant difference in the degree of degradation and the content of extractives in SW and HW was observed. The examined artifacts were then impregnated with five different PEG solutions. It was found that the highest anti-shrink efficiency (ASE) was obtained for one-stage PEG 2000 impregnation. The obtained data of sorption experiments showed that all applied impregnation options guaranteed safe exposure of wood in air relative humidity (RH) lower than 80%. Moreover, one-stage impregnation with PEG 2000 assured the lowest equilibrium moisture content (EMC) of wood, especially SW, at RH above 80%.