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Physical, mechanical and biological properties of thermo-mechanically densified and thermally modified timber using the Vacu3-process

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Abstract

Densification and thermal modification change wood properties in different ways depending on the treatment conditions and the wood species. In the presented investigations, densification and thermal modification were applied consecutively. The primary objective of this treatment combination was the compensation of reduced mechanical properties due to the thermal modification by densification. The combined processes were applied to five European wood species: poplar (Populus nigra L.), beech (Fagus sylvatica L.), Norway spruce (Picea abies Karst.), English oak (Quercus robur L.) and European ash (Fraxinus excelsior L.). Depending on the mean density of the species, a thermo-mechanical densification of 43 or 50% was imposed to improve mechanical strength parallel to the grain. Subsequently, the densified material was thermally modified in the so-called Vacu3-process at 230 °C and 20 or 80% vacuum and at 240 °C and 20% vacuum. The thermal modification resulted in changing wood colour, mechanical strength, hardness, dimensional stability and durability. All the wood modification processes were carried out at industrial scale after pre-tests at laboratory scale. The modified material was characterized regarding flexural properties, static and dynamic hardness, structural integrity, abrasion resistance, moisture dynamics, dimensional stability, and durability against white, brown and soft rot fungi. In summary, the test results showed that the consecutive application of thermo-mechanical densification and thermal modification leads to significantly improved durability whilst mechanical properties at least for beech, ash and poplar remained and the material is dimensionally stable.

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Acknowledgements

The authors gratefully acknowledge the financial support from German Federal Ministry of Education and Research for the Leading-Edge Cluster BioEconomy project VP 1.11—DURAPRESSTIMBER under grant number 031A440A to 031A440D. The authors also thank the partners from industry Deutsche Holzveredelung Schmeing GmbH & Co. KG—Kirchhundem, timura Holzmanufactur GmbH - Rottleberode and terHürne GmbH & Co. KG—Südlohn for collaboration. Jonas Klinger and Ann-Marie Rothschuh are acknowledged for their help with physical and mechanical experiments.

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Authors and Affiliations

  1. School of Civil and Environmental Engineering, Faculty of Civil Engineering, Institute of Steel and Timber Construction, Technical University Dresden, Georg-Schumann-Str. 7, 01187, Dresden, Germany

    Jörg Wehsener, Jens Hartig & Peer Haller

  2. Wood Biology and Wood Products, Georg-August University Göttingen, Büsgenweg 4, 37077, Göttingen, Germany

    Christian Brischke

  3. Faculty of Architecture and Landscape Sciences, Institute of Vocational Sciences in the Building Trade, Leibniz University Hannover, Herrenhäuser Str. 8, 30419, Hannover, Germany

    Linda Meyer-Veltrup

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  1. Jörg Wehsener
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  2. Christian Brischke
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  3. Linda Meyer-Veltrup
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  4. Jens Hartig
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  5. Peer Haller
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Correspondence to Jörg Wehsener.

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Wehsener, J., Brischke, C., Meyer-Veltrup, L. et al. Physical, mechanical and biological properties of thermo-mechanically densified and thermally modified timber using the Vacu3-process. Eur. J. Wood Prod. 76, 809–821 (2018). https://doi.org/10.1007/s00107-017-1278-4

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  • DOI: https://doi.org/10.1007/s00107-017-1278-4

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