Skip to main content

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

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.

This is a preview of subscription content, access via your institution.

Fig. 1
Fig. 2
Fig. 3
Fig. 4

References

  • Adler DC, Bueher MJ (2013) Mesoscale mechanics of wood cell walls under axial strain. Soft Matter 9:7138–7144

    CAS  Article  Google Scholar 

  • Blomberg J, Persson B, Bexell U (2006) Effects of semi-isostatic densification on anatomy and cell-shape recovery on soaking. Holzforschung 60:322–331

    CAS  Article  Google Scholar 

  • 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 56:403–411

    Article  Google Scholar 

  • 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 53:541–546

    CAS  Article  Google Scholar 

  • EN 1534 (2000) Wood and parquet flooring—determination of resistance to indentation (Brinell)—test method. CEN—European Committee for Standardization, Brussels

  • Fratzl P, Burgert I, Keckes J (2004) Mechanical model for the deformation of the wood cell wall. Z Metallkd 95(7):579–584

    CAS  Article  Google Scholar 

  • 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, USA

  • Hill CAS (2006) Wood modification—chemical, thermal and other processes. Wiley, Chichester

    Book  Google Scholar 

  • 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 36:969–975

    Google Scholar 

  • Inoue M, Norimoto M, Tanahashi M, Rowell RM (1993) Steam or heat fixation of compressed wood. Wood Fib Sci 25:224–235

    CAS  Google Scholar 

  • Inoue M, Sekino N, Morooka T, Rowell RM, Norimoto M (2008) Fixation of compressive deformation in wood by pre-steaming. J Trop For Sci 20:273–281

    Google Scholar 

  • Kamke F (2006) Densified Radiata pine for structural composites. Maderas-Cienc Tecnol 8:83–92

    Article  Google Scholar 

  • 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 2:810–814

    CAS  Article  PubMed  Google Scholar 

  • Kellog RM, Wangaard FF (1969) Variation in the cell-wall density of wood. Wood Fib Sci 1:180–204

    Google Scholar 

  • Kutnar A, Kamke F, Sernek M (2009) Density profile and morphology of viscoelastic thermal compressed wood. Wood Sci Technol 43:57–68

    CAS  Article  Google Scholar 

  • 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 71:13–16

    CAS  Article  Google Scholar 

  • Laine K, Segerholm K, Wålinder M, Rautkari L, Ormondroyd G, Hughes M, Jones D (2014) Micromorphological studies of surface densified wood. J Mat Sci 49:2027–2034

    CAS  Article  Google Scholar 

  • 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, Lyngby

    Google Scholar 

  • Navi P, Girardet F (2000) Effects of thermo-hydro-mechanical treatment on the structure and properties of wood. Holzforschung 54:287–293

    CAS  Article  Google Scholar 

  • Navi P, Pittet V, Plummer CJG (2002) Transient moisture effects on wood creep. Wood Sci Technol 36:447–462

    CAS  Article  Google Scholar 

  • 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, Austria

  • Norimoto M, Ota C, Akitsu H, Yamada T (1993) Permanent fixation of bending deformation in wood by heat treatment. Wood Res 79:23–33

    CAS  Google Scholar 

  • 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, Sweden

  • Rautkari L, Kamke F, Hughes M (2011) Density profile in relation to hardness of viscoelastic thermal compressed (VTC) wood composite. Wood Sci Technol 45:693–705

    CAS  Article  Google Scholar 

  • Seborg RM, Stamm AJ (1941) The compression of wood. Forest Products Laboratory, Forest Service US Department of Agriculture, Madison

    Google Scholar 

  • Seborg RM, Tarkow H, Stamm AJ (1953) Effect of heat upon the dimensional stabilisation of wood. J For Prod Res Soc 3:59–67

    CAS  Google Scholar 

  • 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, USA

  • Seltman J (1995) Opening the wood structure by UV-irradiation. Holz Roh Werkst 53:225–228

    Article  Google Scholar 

  • Stamm AJ (1929) Density of wood substance, absorption by wood, and permeability of wood. J Phys Chem 33:398–414

    CAS  Article  Google Scholar 

  • 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, USA

  • 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 1–2:46–51

    Article  Google Scholar 

  • Yano H, Hirose A, Ibana S (1997) High-strength wood-based materials. J Mat Sci 16:1906–1909

    CAS  Google Scholar 

  • 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 102:1672–1680

    CAS  Article  Google Scholar 

Download references

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.

Author information

Authors and Affiliations

Authors

Corresponding author

Correspondence to Kristiina Laine.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

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

Download citation

  • Received:

  • Published:

  • Issue Date:

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

Keywords

  • Compression Ratio
  • Densified Wood
  • Wood Compression
  • Thermal Modification
  • Brinell Hardness