The effect of the drying method on the cell wall structure and sorption properties of waterlogged archaeological wood

Abstract

Drying is a process affecting various wood properties, including its structure, moisture behaviour and mechanical properties. Since waterlogged wooden artefacts usually constitute priceless objects of cultural heritage, understanding the effect of drying on the complex interactions between the wood ultrastructure and the resulting properties is necessary to ensure their proper conservation. Hence, this was the aim of the present study, with a particular emphasis on the influence of drying conditions on the relations between the cell wall structure, dimensional stability and hygroscopicity of degraded archaeological wood. The choice of the particular drying methods was dictated by their final effect on wood appearance (dimensions). The results obtained clearly show that depending on the drying method applied, the resulting material differs significantly in structure, dimensions and sorption properties, despite the same degree of wood degradation. Air- and oven-drying resulted in the highest wood shrinkage, lower porosity, and a decreased number of free hydroxyls in the wood cell wall. The best wood dimensional stabilisation and the highest porosity were ensured by freeze- and supercritical drying. No correlations were found between wood structure and moisture behaviour. The outcome of the research may be useful for conservators who plan to provide the artefacts with proper storage conditions and effective conservation/reconservation.

Effects of Biological and Chemical Degradation on the Properties of Scots Pine Wood—Part I: Chemical Composition and Microstructure of the Cell Wall

“…Degradation also affected the microstructure of the cell walls. It is visible in the approximately twofold increase in the total pore volume and surface area for degraded wood compared with undegraded ( Table 1 ), despite the shrinkage and presumed collapse of the degraded cell walls during drying that undoubtedly reduced both their surface area and pore volume [ 30 ].…”

“…Alterations in the wood cell wall microstructure after biological and chemical degradation were investigated using a nitrogen absorption method [ 28 , 29 , 30 ]. Measurements were performed on a Gemini Surface Area Analyser (Micromeritics Instrument Corporation, Norcross, GA, USA) using de-gassed wood specimens.…”

“…Wood porosity (i.e., total pore volume and their size distribution) was analysed using the Barrett–Joyner–Halenda (BJH) method [ 32 ]. Although the method is not appropriate for measurements of micro- and mesopores with a diameter below 4 nm, we have already shown that it is suitable for making comparisons between analysed samples [ 29 , 30 ]. Micromeritics Stardriver software was employed for all calculations.…”

Conservation of Waterlogged Wood—Past, Present and Future Perspectives

“…Porosity determination of waterlogged wood can be challenging to measure. Techniques, such as nitrogen sorption require dry samples and this risks collapse occurring, even when using methods such a solvent exchange or supercritical drying [90]. Porosity measurements on water-saturated samples, such as solute exclusion, thermoporometry, or NMR relaxation may be compromised by the presence of degradation products in the wood.…”

The Viscoelastic Behaviour of Waterlogged Archaeological Wood Treated with Methyltrimethoxysilane

“…Based on the Brunauer-Emmet-Teller (BET) theory [80], i.e., the volume of nitrogen absorbed on the surface of the cell walls at different partial pressures, the surface area was calculated using Micromeritics Stardriver software. Wood porosity was analysed using the Barrett-Joyner-Halenda (BJH) method [81], which is appropriate for making comparisons between analysed samples and gives reliable results for meso-and macropores with diameters above 4 nm [39,82].…”