Influence of process conditions on hygroscopicity and mechanical properties of European beech thermally modified in a high-pressure reactor system

Research output: Contribution to journalArticle


Research units

  • University of Göttingen


European beech (Fagus sylvatica L.) was thermally modified in a closed reactor system under various process conditions. Sorption cycles, dynamic vapor sorption (DVS) measurements, and a three-point bending test were performed on thermally modified wood (TMW) to assess hygroscopicity and mechanical properties. As a function of mass loss (ML), the initial equilibrium moisture content (EMC) measured at 20°C/65% relative humidity (RH) directly after the process was strongly influenced by the RH during the process. This effect is explained by realignments of amorphous polymers in the cell wall ultra-structure in the course of thermal modification (TM). However, the EMC of TMW gradually increased after sorption cycles consisting of conditioning over liquid water and water-soaking. This increase was most distinct for TMW modified at low RH, which is an indication for reversible ultra-structural realignments. Results of the bending test suggest that structural realignments also hindered the plastic flow of amorphous cell wall polymers, thereby reducing inelastic toughness and inelastic deflection, while other bending properties were solely affected by ML alone. Process conditions in a closed reactor systems have a profound impact on resulting wood properties, and thus, the partial reversibility of these property changes need to be considered during the application.


Original languageEnglish
Pages (from-to)971-979
Number of pages9
Issue number10
Publication statusPublished - 1 Oct 2016
MoE publication typeA1 Journal article-refereed

    Research areas

  • dynamic vapor sorption (DVS), equilibrium moisture content (EMC), hygroscopicity, mass loss, relative humidity, static bending test, thermally modified wood, water vapor pressure

ID: 11745553