Wood Science and Technology

, Volume 50, Issue 5, pp 883–894 | Cite as

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

  • Kristiina Laine
  • Kristoffer Segerholm
  • Magnus Wålinder
  • Lauri Rautkari
  • Mark Hughes


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.


Compression Ratio Densified Wood Wood Compression Thermal Modification Brinell Hardness 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



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.


  1. Adler DC, Bueher MJ (2013) Mesoscale mechanics of wood cell walls under axial strain. Soft Matter 9:7138–7144CrossRefGoogle Scholar
  2. Blomberg J, Persson B, Bexell U (2006) Effects of semi-isostatic densification on anatomy and cell-shape recovery on soaking. Holzforschung 60:322–331CrossRefGoogle Scholar
  3. Dwianto W, Norimoto M, Morooka T, Tanaka F, Inoue M, Liu Y (1998) Radial compression of Sugi wood (Cryptomeria japonica D. Don). Holz Roh Werkst 56:403–411CrossRefGoogle Scholar
  4. Dwianto W, Morooka T, Norimoto M, Kitajima T (1999) Stress relaxation of Sugi (Cryptomeria japonica D. Don) wood in radial compression under high temperature steam. Holzforschung 53:541–546CrossRefGoogle Scholar
  5. EN 1534 (2000) Wood and parquet flooring—determination of resistance to indentation (Brinell)—test method. CEN—European Committee for Standardization, BrusselsGoogle Scholar
  6. Fratzl P, Burgert I, Keckes J (2004) Mechanical model for the deformation of the wood cell wall. Z Metallkd 95(7):579–584CrossRefGoogle Scholar
  7. Gong M, Nakatani M, Yang Y, Afzal M (2006) Maximum compression ratios of softwoods produced in eastern Canada. In: Proceedings of the 9th World Conference on Timber Engineering, Portland, USAGoogle Scholar
  8. Hill CAS (2006) Wood modification—chemical, thermal and other processes. Wiley, ChichesterCrossRefGoogle Scholar
  9. Inoue M, Norimoto M, Otsuka Y, Yamada T (1990) Surface compression of coniferous lumber I. A new technique to compress the surface layer. Moguzai Gakkaishi 36:969–975Google Scholar
  10. Inoue M, Norimoto M, Tanahashi M, Rowell RM (1993) Steam or heat fixation of compressed wood. Wood Fib Sci 25:224–235Google Scholar
  11. Inoue M, Sekino N, Morooka T, Rowell RM, Norimoto M (2008) Fixation of compressive deformation in wood by pre-steaming. J Trop For Sci 20:273–281Google Scholar
  12. Kamke F (2006) Densified Radiata pine for structural composites. Maderas-Cienc Tecnol 8:83–92CrossRefGoogle Scholar
  13. Keckes J, Burgert I, Frümann K, Müller M, Köln K, Hamilton M, Burghammer M, Roth SV, Stanzl-Tschegg S, Fratzl P (2003) Cell-wall recovery after irreversible deformation of wood. Nat Mater 2:810–814CrossRefPubMedGoogle Scholar
  14. Kellog RM, Wangaard FF (1969) Variation in the cell-wall density of wood. Wood Fib Sci 1:180–204Google Scholar
  15. Kutnar A, Kamke F, Sernek M (2009) Density profile and morphology of viscoelastic thermal compressed wood. Wood Sci Technol 43:57–68CrossRefGoogle Scholar
  16. Laine K, Rautkari L, Hughes M (2013) The effect of process parameters on the hardness of surface densified Scots pine solid wood. Eur J Wood Prod 71:13–16CrossRefGoogle Scholar
  17. Laine K, Segerholm K, Wålinder M, Rautkari L, Ormondroyd G, Hughes M, Jones D (2014) Micromorphological studies of surface densified wood. J Mat Sci 49:2027–2034CrossRefGoogle Scholar
  18. Morsing N (2000) Densification of wood: the influence of hygrothermal treatment on compression of beech perpendicular to the grain. vol 79. Technical university of Denmark, LyngbyGoogle Scholar
  19. Navi P, Girardet F (2000) Effects of thermo-hydro-mechanical treatment on the structure and properties of wood. Holzforschung 54:287–293CrossRefGoogle Scholar
  20. Navi P, Pittet V, Plummer CJG (2002) Transient moisture effects on wood creep. Wood Sci Technol 36:447–462CrossRefGoogle Scholar
  21. Niemz P, Stübi T (2000) Investigations of hardness measurements on wood based materials using a new universal measurement system. In: Proceedings of the symposium on wood machining, properties of wood and wood composites related to wood machining, Vienna, AustriaGoogle Scholar
  22. Norimoto M, Ota C, Akitsu H, Yamada T (1993) Permanent fixation of bending deformation in wood by heat treatment. Wood Res 79:23–33Google Scholar
  23. Rautkari L, Hughes M (2009) Eliminating set-recovery in densified wood using a steam heat-treatment process. In: Proceedings of the 4th European conference on wood modification. Stockholm, SwedenGoogle Scholar
  24. Rautkari L, Kamke F, Hughes M (2011) Density profile in relation to hardness of viscoelastic thermal compressed (VTC) wood composite. Wood Sci Technol 45:693–705CrossRefGoogle Scholar
  25. Seborg RM, Stamm AJ (1941) The compression of wood. Forest Products Laboratory, Forest Service US Department of Agriculture, MadisonGoogle Scholar
  26. Seborg RM, Tarkow H, Stamm AJ (1953) Effect of heat upon the dimensional stabilisation of wood. J For Prod Res Soc 3:59–67Google Scholar
  27. Seborg RM, Millet MA, Stamm AJ (1956) Heat-stabilized compressed wood (Staypak). Report no: 1580. Forest Products Laboratory, Forest Service US Department of Agriculture, Madison, WI, USAGoogle Scholar
  28. Seltman J (1995) Opening the wood structure by UV-irradiation. Holz Roh Werkst 53:225–228CrossRefGoogle Scholar
  29. Stamm AJ (1929) Density of wood substance, absorption by wood, and permeability of wood. J Phys Chem 33:398–414CrossRefGoogle Scholar
  30. Stamm AJ, Seborg RM (1942) Resin-treated wood (Impreg). Report no: 1380 (Revised 1962). Forest Products Laboratory, Forest Service US Department of Agriculture, Madison, WI, USAGoogle Scholar
  31. Wålinder M, Omidvar A, Seltman J, Segerholm K (2009) Micromorphological studies of modified wood using a surface preparation technique based on ultraviolet laser ablation. Wood Mat Sci Eng 1–2:46–51CrossRefGoogle Scholar
  32. Yano H, Hirose A, Ibana S (1997) High-strength wood-based materials. J Mat Sci 16:1906–1909Google Scholar
  33. Zhang Y, Zhang SY, Chui YH, Wan H, Bousmina M (2006) Wood plastic composites by melt impregnation: polymer retention and hardness. J Appl Polym Sci 102:1672–1680CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2016

Authors and Affiliations

  • Kristiina Laine
    • 1
  • Kristoffer Segerholm
    • 1
    • 2
  • Magnus Wålinder
    • 1
  • Lauri Rautkari
    • 3
  • Mark Hughes
    • 3
  1. 1.Department of Civil and Architectural EngineeringKTH Royal Institute of TechnologyStockholmSweden
  2. 2.SP Technical Research Institute of SwedenStockholmSweden
  3. 3.Department of Forest Products TechnologyAalto UniversityEspooFinland

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