Abstract
Abstract The moisture-induced recovery of compressed wood is one of the major problems of wood densification technology. Achieving a cost-efficient surface densification process without the need for additional resins to eliminate the set-recovery may lead to an increase in value of low-density wood species. A previous study has shown that a pre-treatment with ionic liquids (ILs) can nearly eliminate the set-recovery. It was however observed that during the pre-treatment process the IL did not penetrate sufficiently deep into the wood to explain the achieved reduction in set-recovery. Based on these findings, the hypothesis was posed that further penetration of the IL into the wood occurs during the densification stage as a consequence of the applied heat and pressure. Thermo-gravimetric analysis (TGA) and gas-chromatography mass-selective-detection (GC-MSD) showed that the depth of penetration of the IL was greater after the densification process than before. Digital image correlation (DIC) showed that in regions with a high IL concentration, there was almost no set-recovery, and it gradually increased with a decrease in the IL concentration, as observed with TGA and GC-MSD analysis.
Highlights
Surface densification, i.e. compression in the transverse direction, of Scots pine sawn timber can lead to a more than twofold increase in surface density, resulting in a hardness level comparable to more expensive wood species, such as oak (Rautkari et al 2013)
Digital image correlation (DIC) showed that in regions with a high ionic liquids (ILs) concentration, there was almost no set-recovery, and it gradually increased with a decrease in the IL concentration, as observed with Thermo-gravimetric analysis (TGA) and gaschromatography mass-selective-detection (GC-MSD) analysis
Densifying only a relatively thin layer of the wood, as opposed to bulk-densification, reduces the needed process resources and maintains a larger share of the wood volume, without detrimental effects on the desired improvement of the material properties. This potentially facilitates the development of a large-scale and commercially viable surface densification process, which would open up new market opportunities for widely available low-density wood species, among them Scots pine
Summary
I.e. compression in the transverse direction, of Scots pine sawn timber can lead to a more than twofold increase in surface density, resulting in a hardness level comparable to more expensive wood species, such as oak (Rautkari et al 2013). Densifying only a relatively thin layer of the wood, as opposed to bulk-densification, reduces the needed process resources and maintains a larger share of the wood volume, without detrimental effects on the desired improvement of the material properties. This potentially facilitates the development of a large-scale and commercially viable surface densification process, which would open up new market opportunities for widely available low-density wood species, among them Scots pine. When subsequently exposed to moisture, the matrix re-plasticises, This work is licensed under the Creative Commons Attribution 4.0
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