Effect of a thermo-mechanical densification process on selected properties of densified wood of Tasmanian oak and Eucalyptus nitens

Regrowth Tasmanian oak and Eucalyptus nitens are fast-growing Australian plantation hardwoods widely cultivated in Tasmania. Despite their favourable physical and aesthetic properties, their relatively low density limits use to wood-chip production and minor interior applications. This study aimed to enhance the material properties of these species through thermo-mechanical densification. The effects of compression ratio, pressing time, and pressing temperature were evaluated on color change, set recovery (wet and dry), pull-off strength, and delamination. Eucalyptus nitens showed excellent color stability under all conditions (ΔE*ab < 5), while Tasmanian oak exhibited significant darkening at 175 °C (ΔE*ab 6.17–9.06). At 175 °C and 37% compression, E. nitens responded more strongly, achieving a mean wet-use set recovery of 0.0%, compared with 2.7% for Tasmanian oak. Both species showed significantly improved dimensional stability at 37% compression ratio compared to 25%. The highest F-values observed for Eucalyptus nitens and Tasmanian oak were 25.36 and 17.91, respectively. Increased compression also improved pull-off strength in both species, but in Tasmanian oak, extractive migration at 175 °C likely reduced coating adhesion. The densification process had minimal impact on bondability overall. However, a higher pressing temperature significantly reduced delamination in Tasmanian oak (P-value 0.031), while showing negligible effect in Eucalyptus nitens. The results suggest that both Eucalyptus nitens and Tasmanian oak species were stable following the densification process and would make the densified wood serviceable under conditions in which the EMC does not exceed 17% if unprotected. Statements and Declarations. All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Benoit Belleville. The first draft of the manuscript was written by Benoit Belleville and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. The authors have no relevant financial or non-financial interests to disclose. The authors have no competing interests to declare that are relevant to the content of this article. All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript. The authors have no financial or proprietary interests in any material discussed in this article.