European Journal of Wood and Wood Products

, Volume 76, Issue 3, pp 809–821 | Cite as

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

  • Jörg Wehsener
  • Christian Brischke
  • Linda Meyer-Veltrup
  • Jens Hartig
  • Peer Haller


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.



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.


  1. Bekhta P, Niemz P (2003) Effect of high temperature on the change in color, dimensional stability and mechanical properties of spruce wood. Holzforschung 57:539–546CrossRefGoogle Scholar
  2. Blomberg J, Persson B, Blomberg A (2005) Effects of semi-isostatic densification of wood on the variation in strength properties with density. Wood Sci Technol 39:339–350CrossRefGoogle Scholar
  3. Bravery AF (1979) A miniaturised wood-block test for the rapid evaluation of preservative fungicides. Proceedings of a special seminar held in association with the 10th annual meeting of the IRG, Peebles, Rep. No. 136. Swedish Wood Preservation Institute, StockholmGoogle Scholar
  4. Brischke C, Meyer-Veltrup L (2016) Performance of thermally modified wood during 14 years of outdoor exposure. Int Wood Prod J 7:89–95CrossRefGoogle Scholar
  5. Brischke C, Koch S, Rapp AO, Welzbacher CR (2005) Surface properties of thermally treated wood—wear, abrasion and hardness. In: Militz H, Hill C (eds) Wood modification: processes, properties and commercialisation. Proceedings of the 2nd European Conference on Wood Modification, Göttingen, Germany, 6–7 October 2005, pp 371–375Google Scholar
  6. Brischke C, Rapp AO, Welzbacher CR (2006) High-energy multiple impact (HEMI)-test—part 1: a new tool for quality control of thermally modified timber. International Research Group on Wood Protection, Document No. IRG-WP-06–20346Google Scholar
  7. Burmester A (1973) Effect of heat-pressure treatments of semidry wood on its dimensional stability. Holz Roh-Werkst 31:237–243CrossRefGoogle Scholar
  8. CEN/TS 15083-1 (2005) Durability of wood and wood-based products—determination of the natural durability of solid wood against wood-destroying fungi, test methods—part 1: basidiomycetes. CEN (European Committee for Standardization), BrusselsGoogle Scholar
  9. CEN/TS 15083-2 (2005) Durability of wood and wood-based products—determination of the natural durability of solid wood against wood-destroying fungi, test methods—part 2: soft rotting micro-fungi. CEN (European Committee for Standardization), BrusselsGoogle Scholar
  10. Chaouch M, Dumarçay S, Pétrissans A, Pétrissans M, Gérardin P (2013) Effect of heat treatment intensity on some conferred properties of different European softwood and hardwood species. Wood Sci Technol 47:663–673CrossRefGoogle Scholar
  11. DIN 52186 (1978) Testing of wood, bending test, Beuth Verlag GmbH, BerlinGoogle Scholar
  12. EN 113 (1996) Wood preservatives—method of test for determining the protective effectiveness against wood destroying basidiomycetes—determination of the toxic values. CEN (European Committee for Standardization), BrusselsGoogle Scholar
  13. EN 1534 (2010) Wood flooring—determination of resistance to indentation—test method. CEN (European Committee for Standardization), BrusselsGoogle Scholar
  14. EN 350 (2016) Durability of wood and wood-based products—testing and classification of the resistance to biological agents, the permeability to water and the performance of wood and wood-based materials. CEN (European Committee for Standardization), BrusselsGoogle Scholar
  15. Hakkou M, Pétrissans M, Gérardin P, Zoulalian A (2006) Investigations of the reasons for fungal durability of heat-treated beech wood. Polym Degrad Stab 91:393–397CrossRefGoogle Scholar
  16. Haller P, Wehsener J (2004) Festigkeitsuntersuchungen an Fichtenpressholz (FPH) (Mechanical properties of densified spruce) (In German). Holz Roh-Werkst 62:452–454Google Scholar
  17. Heger F, Groux M, Girardet F, Welzbacher C, Rapp AO, Navi P (2004) Mechanical and durability performance of THM-densified wood. In: Proceedings of the Final Workshop of COST Action E 22, 22–23 March 2004, Estoril, PortugalGoogle Scholar
  18. Hill CA (2006) Wood modification: chemical, thermal and other processes. Wiley, ChichesterCrossRefGoogle Scholar
  19. Hill CA, Ramsay J, Keating B, Laine K, Rautkari L, Hughes M, Constant B (2012) The water vapour sorption properties of thermally modified and densified wood. J Mater Sci 47:3191–3197CrossRefGoogle Scholar
  20. Inoue M, Norimoto M, Tanahashi M, Rowell RM (1993) Steam or heat fixation of compressed wood. J Wood Fiber Sci 25:224–235Google Scholar
  21. ISO 5223 (1996) Test sieves for cereals. International Organization for Standardization, GeneveGoogle Scholar
  22. Ito Y, Tanahashi M, Shigematsu M, Shinoda Y, Otha C (1998) Compressive-molding of wood by high-pressure steam-treatment. Part 1: development of compressively molded scares from thinnings. Holzforschung 52:211–216CrossRefGoogle Scholar
  23. Kariz M, Kuzman MK, Sernek M, Hughes M, Rautkari L, Kamke FA, Kutnar A (2017) Influence of temperature of thermal treatment on surface densification of spruce. Eur J Wood Prod 75:113–123CrossRefGoogle Scholar
  24. Kollmann FP (1936) Technologie des Holzes (Technology of wood) (In German). Springer, BerlinGoogle Scholar
  25. Korkut S, Akgül M, Dündar T (2008) The effects of heat treatment on some technological properties of Scots pine (Pinus sylvestris L.) wood. Biores Technol 99:1861–1868CrossRefGoogle Scholar
  26. Kutnar A, Kamke FA, Sernek M (2008) The mechanical properties of densified VTC wood relevant for structural composites. Holz Roh Werkst 66:439–446CrossRefGoogle Scholar
  27. Kutnar A, Kamke FA, Sernek M (2009) Density profile and morphology of viscoelastic thermal compressed wood. Wood Sci Technol 43:57–68CrossRefGoogle Scholar
  28. 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
  29. Laine K, Segerholm K, Wålinder M, Rautkari L, Hughes M (2016) Wood densification and thermal modification: hardness, set-recovery and micromorphology. Wood Sci Technol 50:883–894CrossRefGoogle Scholar
  30. Lamason C, Gong M (2007) Optimization of pressing parameters for mechanically surface-densified aspen. Forest Prod J 57:64–68Google Scholar
  31. Metsä-Kortelainen S, Paajanen L, Viitanen H (2011) Durability of thermally modified Norway spruce and Scots pine in above-ground conditions. Wood Mat Sci Eng 6:163–169CrossRefGoogle Scholar
  32. Meyer L, Brischke C, Welzbacher CR (2011) Dynamic and static hardness of wood: method development and comparative studies. Int Wood Prod J 2:5–11CrossRefGoogle Scholar
  33. Meyer-Veltrup L, Brischke C, Alfredsen G, Humar M, Flæte P-O, Isaksson T, Larsson Brelid P, Westin M, Jermer J (2017) The combined effect of wetting ability and durability on outdoor performance of wood: development and verification of a new prediction approach. Wood Sci Technol 51(3):615–637CrossRefGoogle Scholar
  34. Militz H (2002) Heat treatment of wood: European Processes and their background. Document No. IRG/WP 02–40241. The International Research Group on Wood Preservation, Cardiff, WalesGoogle Scholar
  35. Navi P, Heger F (2004) Combined densification and thermo-hygro-mechanical processing of wood. MRS Bull 29:332–336CrossRefGoogle Scholar
  36. Olek W, Majka J, Czajkowski Ł (2013) Sorption isotherms of thermally modified wood. Holzforschung 67:183–191CrossRefGoogle Scholar
  37. Rautkari L, Laine K, Kutnar A, Medved S, Hughes M (2013) Hardness and density profile of surface densified and thermally modified Scots pine in relation to degree of densification. J Mater Sci 48:2370–2375CrossRefGoogle Scholar
  38. Sandberg D, Haller P, Navi P (2013) Thermo-hydro and thermo-hydro-mechanical wood processing: an opportunity for future environmentally friendly wood products. Wood Mat Sci Eng 8:64–88CrossRefGoogle Scholar
  39. Sell J (1997) Eigenschaften und Kenngrößen von Holzarten (Properties and characteristic variables of wood species) (In German). 4th edn. Baufachverlag Lignum, ZürichGoogle Scholar
  40. Stamm AJ, Burr HK, Kline AA (1946) Staybwood. Heat-stabilized wood. Ind Eng Chem 38:630–634CrossRefGoogle Scholar
  41. Tjeerdsma BF, Boonstra M, Pizzi A, Tekely P, Militz H (1998) Characterisation of thermal modified wood: molecular reasons for wood performance improvement. CPMAS 13C NMR characterisation of thermal modified wood. Holz Roh-Werkst 56:149–153CrossRefGoogle Scholar
  42. Van Acker J, De Windt I, Li W, Van den Bulcke J (2014) Critical parameters on moisture dynamics in relation to time of wetness as factor in service life prediction. International Research Group on Wood Protection, Document No. IRG-WP-14-20555Google Scholar
  43. Vorreiter L (1958) Holztechnologisches Handbuch Band 2: System Holz-, Wasser-, Wärme, Holztrocknung, Dämpfen und Kochen. Spanlose Holzverformung (Handbook of wood technology, vol. 2) (In German). Verlag Georg Fromme & Co, Wien & MünchenGoogle Scholar
  44. Wehsener J, Weser T, Haller P, Diestel O, Cherif C (2014) Textile reinforcement of multidimensional formable wood. Eur J Wood Prod 72(4):463–475CrossRefGoogle Scholar
  45. Welzbacher CR, Brischke C, Rapp AO (2007) Influence of treatment temperature and duration on selected biological, mechanical, physical and optical properties of thermally modified timber. Wood Mater Sci Eng 2:66–76CrossRefGoogle Scholar
  46. Welzbacher CR, Wehsener J, Rapp AO, Haller P (2008) Thermo-mechanical densification combined with thermal modification of Norway spruce (Picea abies Karst) in industrial scale-dimensional stability and durability aspects. Holz Roh-Werkst 66:39–49CrossRefGoogle Scholar
  47. Welzbacher CR, Rassam G, Talaei A, Brischke C (2011) Microstructure, strength and structural integrity of heat-treated beech and spruce wood. Wood Mat Sci Eng 6:219–227CrossRefGoogle Scholar

Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2017

Authors and Affiliations

  1. 1.School of Civil and Environmental Engineering, Faculty of Civil Engineering, Institute of Steel and Timber ConstructionTechnical University DresdenDresdenGermany
  2. 2.Wood Biology and Wood ProductsGeorg-August University GöttingenGöttingenGermany
  3. 3.Faculty of Architecture and Landscape Sciences, Institute of Vocational Sciences in the Building TradeLeibniz University HannoverHannoverGermany

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