Acquisition of sorption isotherms for modified woods by the use of dynamic vapour sorption instrumentation. Principles and Practice

The complex wood-water relationship has been the topic of numerous studies. Sorption isotherms – in particular – have been derived for hundreds of wood species, their sap- and heartwood sections as well as for decayed, engineered and modified wood materials. However, the traditional methods for obtaining sorption isotherms are very time consuming. With new dynamic vapour sorption (DVS) instrumentation, the acquisition of data for constructing sorption isotherms is suddenly dramatically lowered. Where the traditional methods often required months, data can now be obtained in a matter of days depending on the number of data points required. The fast data acquisition makes DVS a useful tool in studying the sorption properties of wood, and especially in studying the effect of different modification treatments on these properties. This study includes an investigation of the sorption properties of heat treated and acetylated softwood. The results of both are compared with results for untreated softwood, and general remarks regarding the acquisition and interpretation of sorption data are made. It is pointed out that care must be taken when interpreting results such as desorption isotherms not commencing from full water saturation. The sorption properties of heat treated Scots pine (Celloc) and acetylated Radiata pine (Accoya) showed a greater hysteresis effect for the previous than both acetylated and untreated softwood. Furthermore, the effectiveness of the different modification treatments was quantified by the reduction in moisture content relative to untreated Scots pine sapwood. This may be used in future documentation of the resistance of modified wood to fungal decay.