Journal
EUROPEAN JOURNAL OF WOOD AND WOOD PRODUCTS
Volume 80, Issue 4, Pages 859-876Publisher
SPRINGER
DOI: 10.1007/s00107-022-01828-0
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Funding
- University of Natural Resources and Life Sciences Vienna (BOKU)
- European Union's Horizon 2020 research and innovation programme [773324]
- Federal Ministry BMK
- Federal Ministry BMDW
- Province of Styria within the COMET-Competence Centers for Excellent Technologies programme
- companies ACstyria Mobilitatscluster GmbH
- Collano AG
- IB STEINER
- DYNAmore Gesellschaft fur FEM Ingenieurdienstleistungen mbH
- EJOT Austria GmbH Co KG
- Forst-Holz-Papier
- Fill Gesellschaft m. b.H
- Glanzstoff Management Consulting GmbH
- Holzcluster Steiermark GmbH
- Klumpp Coatings GmbH
- LEAN Management Consulting GmbH
- Volkswagen AG
- Weitzer Wood Solutions GmbH
- Austrian Research Promotion Agency [FFG 882.509]
- Styrian Business Promotion Agency [SFG 1.000.065.896]
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Wood is an efficient material in terms of mechanics, but often falls behind metals and engineered composites in terms of absolute mechanical properties. Densification is a promising approach to improve the mechanical properties of wood. This study investigated the densification of spruce, beech, and poplar wood through a two-step process involving chemical treatment and hot pressing. The results showed that chemically treated and densified wood exhibited better dimensional stability and improved strength.
Regarding mechanics, wood is one of the most efficient materials available. Due to its unique combination of composite and cellular microstructure, it exhibits superb specific mechanical properties which exceed many man-made materials. However, concerning absolute mechanical properties, wood is often inferior to metals and novel engineered composites. Since many wood properties are strongly correlated with its density, densification is a promising pathway towards improved absolute mechanics. Spruce, beech and poplar wood were densified in a two-step process. First, amorphous wood polymers were partially extracted according to an alkaline (AL) and an organosolv (OS) protocol. Subsequently, partially delignified veneers were densified by hot pressing in tangential direction. After densification, average densities increased to 1.00-1.20 g cm(-3). FTIR analysis confirmed chemical changes, mostly in the bands attributed to hemicelluloses and lignin, of chemically treated and hot-pressed veneers. To evaluate the modification process regarding mechanics, tensile and bending properties were characterized and revealed promising results. Compared to untreated control specimens, stiffness and strength tested in tension and bending improved, regardless of wood species and pretreatment. Regarding average tensile properties, the OS treatment improved stiffness, up to 40 GPa, whereas the AL treatment improved strength, up to 300 MPa. Set-recovery tests showed, that chemically treated and densified samples exhibited a better dimensional stability compared to H2O-soaked and compressed specimens. However, 24 h water soaking resulted in excessive thickness swelling. This might be a major drawback of partially delignified and densified wood and should be considered in a material selection process.
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