Katrin Zimmer
Research Scientist
Biography
Katrin Zimmer is a research scientist in the Department of Forest Operations and Digitalization. She has over 20 years of experience in the use of wood. She is an educated carpenter, studied Wood Science and Technology at the University of Hamburg, and has a PhD from the University of Life Sciences on the topic “Variation of treatability of Scots Pine sapwood from Northern Europe”.
Katrin Zimmer focusses her work on the use of underutilized wood species, such as birch, with a focus on material development and growth-specific material properties. She is also responsible for the communication activities of the NIBIO-hosted SFI SmartForest.
Abstract
This study investigates the moisture-induced recovery of temporary property changes in thermo-mechanically densified (TMD) birch and aspen wood, compared to thermally modified (TM) wood. Both treatments were prepared under identical thermal conditions, differing only by compression in TMD. Dimensional stability, water vapour sorption, and Brinell hardness were assessed before and after repeated wetting and drying cycles to evaluate the effect of stress storage in the polymer matrix and its recovery during moisture exposure. The results indicate that both TMD and TM treatments induce a temporary reduction in moisture uptake, consistent with the formation of an annealed polymer structure. Water saturation and subsequent drying restored higher moisture content and reduced Brinell hardness in TMD wood, highlighting a moisture-driven recovery of the annealed polymer conformation. Notably, the decrease in hardness could not be attributed solely to the reduction in bulk density, indicating additional effects of polymer plasticisation. The presence of compression stresses during TMD appeared to enhance stress storage, thereby influencing the recovery of moisture-induced properties. Initial wood moisture content before TMD had little effect on the temporary reduction in moisture content, suggesting that annealing also occurs in dry states. These findings emphasise the need to account for moisture cycling in TMD wood’s service life. Future work should focus on the interplay between compression stresses and the annealing effect to reduce the temporary nature of the property improvements by TMD.
Authors
Katrin ZimmerAbstract
No abstract has been registered
Authors
Katrin ZimmerAbstract
No abstract has been registered
