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Wood densification and thermal modification: hardness, set-recovery and micromorphology

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Abstract

The density of wood can be increased by compressing the porous structure under suitable moisture and temperature conditions. One aim of such densification is to improve surface hardness, and therefore, densified wood might be particularly suitable for flooring products. After compression, however, the deformed wood material is sensitive to moisture, and in this case, recovered up to 60 % of the deformation in water-soaking. This phenomenon, termed set-recovery, was reduced by thermally modifying the wood after densification. This study presents the influence of compression ratio (CR = 40, 50, 60 %) and thermal modification time (TM = 2, 4, 6 h) on the hardness and set-recovery of densified wood. Previously, set-recovery has mainly been studied separately from other properties of densified wood, while in this work, set-recovery was also studied in relation to hardness. The results show that set-recovery was almost eliminated with TM 6 h in the case of CR 40 and 50 %. Hardness significantly increased due to densification and even doubled compared to non-densified samples with a CR of 50 %. Set-recovery reduced the hardness of densified (non-TM) wood back to the original level. TM maintained the hardness of densified wood at an increased level after set-recovery. However, some reduction in hardness was recorded even if set-recovery was almost eliminated.

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Acknowledgments

The authors would like to thank Joachim Seltman (SP, Sweden) and Niko Tuominen (Aalto University) for technical support. The study was supported by the EcoBuild Centre, Stiftelsen Nils och Dorthi Troëdssons forsknings fond and the Finnish Cultural Foundation.

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Authors and Affiliations

  1. Department of Civil and Architectural Engineering, KTH Royal Institute of Technology, Brinellvägen 23, 100 44, Stockholm, Sweden

    Kristiina Laine, Kristoffer Segerholm & Magnus Wålinder

  2. SP Technical Research Institute of Sweden, Drottning Kristinas väg 67, Box 5609, 114 86, Stockholm, Sweden

    Kristoffer Segerholm

  3. Department of Forest Products Technology, Aalto University, Vuorimiehentie 1, 02150, Espoo, Finland

    Lauri Rautkari & Mark Hughes

Authors
  1. Kristiina Laine
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  2. Kristoffer Segerholm
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  3. Magnus Wålinder
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  4. Lauri Rautkari
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  5. Mark Hughes
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Correspondence to Kristiina Laine.

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Laine, K., Segerholm, K., Wålinder, M. et al. Wood densification and thermal modification: hardness, set-recovery and micromorphology. Wood Sci Technol 50, 883–894 (2016). https://doi.org/10.1007/s00226-016-0835-z

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  • DOI: https://doi.org/10.1007/s00226-016-0835-z

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