Surface densification has the potential to greatly increase the hardness of the outer parts of wood material, and thereby also increase the value of low-density species such as Scots pine and Norway spruce, which are found to a great extent in boreal forests. The density, strength and hardness of these species are lower in comparison to commonly used hardwood species such as oak, and the use in applications such as flooring is rather limited. Through densification, a significant improvement in the mechanical properties can be achieved, thereby opening new fields of application.
An important aspect related to densified wood is how to eliminate the set-recovery after pressing, especially when the densified wood is exposed to a moisture variation. Research has shown that it is possible to greatly reduce set-recovery by thermal post-treatment of the densified wood material.
Only limited attention has, however, been on the economic and environmental aspects of the densification process. So far, surface densification processes are time-consuming batch processes, where a post-treatment stage is necessary in order to reduce set-recovery. This means that low value wood species become not only a high value product but also a high cost product, which eliminates their potential advantage over domestic and more expensive hardwood species such as oak and beech, or high-density tropical woods.
The objective of the research project proposed by Luleå University of Technology is the development of a continuous wood surface densification process, where the process time should be considerable shortened and the energy consumption lowered, in order to reduce the costs and environmental impact.
In the near future, the project will focus on evaluating the process from both an economic and an environmental perspective, i.e. transforming a laboratory process into an industrial process, and on evaluating the environmental impact.
Keywords: roller pressing, wood modification, compression, thermo hydro mechanical processing
Authors
Neyses B.
Wood Science and Engineering, Luleå University of Technology, Skellefteå, Sweden
Sandberg D.
Wood Science and Engineering, Luleå University of Technology, Skellefteå, Sweden
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