1. Use of thermally modified wood in building constructions Prof.dr. Franc Pohleven franc.pohleven@bf.uni-lj.si University of Ljubljana Biotechnical Faculty, Department of Wood Science and Technology, Rožna dolina, Cesta VIII/34 SI1000 Ljubljana, Slovenia

2. INTRODUCTION Different wood modification process: Thermal Chemical Enzimatic

4. INTRODUCTION DIFFERENT HEATING MEDIA: nitrogen, steam, oil VACUUM – A SLOVENIAN METHOD Exposure to high temperatures cause severe degradation of cellulose and losses in mechanical properties

5. INTRODUCTION Temperatures from 160 °C to 260 °C Absence of oxygen Process of wood modification Chemical changes in wood cell walls Changes of wood (=modified wood)

6. Phases of process (24 h) drying at 103 °C vacuuming up to 0,05 bar heating to 150 °C heating to T of modif. (3 h) cooling down MATERIALS AND METHODS - modification SOFTWOOD or HARDWOOD

7. PROPERTIES OF THERMALLY MODIFIED WOOD Improvement of durability and dimensional stability Removing of resins Improvement of resonant (acoustic) properties Mass loss Change of physical properties: Colour Reduction of strength and stiffness Bending strength 10 % – 50 %

8. Results - change of colour

9. S B H

10. Elm wood

11. MASS LOSSES Spruce:3 % (190 °C) – 24 % (230 °C) Larch:5 % (190 °C) – 31 % (230 °C)

12. MATERIALS AND METHODS – decay tests DECAY TESTS mini-block test (Bravery) cross-section: 10 mm × 5 mm length: 30 mm Gloeophyllum trabeum Coniophora puteana exposure: 8 weeks

13. Mass loss (%) GtCp Spruceuntreated35,2±5,456±12 treated1,5±1,18,9±4,4 Larchuntreated34,2±7,729,0±2,9 treated1,17±0,180,90±0,21 DECAY – samples treated at 200 °C RESULTS – decay tests

14. MATERIALS AND METHODS – dimensional stability DIMENSIONAL STABILITY ASE – soaking/ovendrying test (3 cycles) shrinkage (α) in r, t dim. 20 mm × 20 mm × 20 mm

15. 50 mm × 20 mm × 20 mm unoriented ABSORPTION OF WATER VAPOUR AT 83 % AIR HUMIDITY AND T = 25 °C

16. Exposure at 83 % RH and 25 °C

17. RESULTS: absorption of water vapour – spruce wood

18. RESULTS: absorption of water vapour – beech wood

19. RESULTS: absorption of water vapour – oak wood

20. DIMENSIONAL STABILITY (spruce)

21. DIMENSIONAL STABILITY (beech)

22. DIMENSIONAL STABILITY (oak)

23. APPROXIMATION OF REDUCTION OF DIMENSIONS OF MODIFIED WOOD SPECIMENS (spruce)

24. APPROXIMATION OF REDUCTION OF DIMENSIONS OF MODIFIED WOOD SPECIMENS (beech)

25. APPROXIMATION OF REDUCTION OF DIMENSIONS OF MODIFIED WOOD SPECIMENS (oak)

26. MATERIALS AND METHODS – MOE AND MOR MOE, MOR static three-point bending test 300 mm × 20 mm x 20 mm, absolute dry Zwick Z-100 10 mm/min

27. MATERIALS AND METHODS - MOE MOE non-destructively natural vibration analysis in clamped-free conditions 300 × mm 20 mm × 10 mm, absolute dry

28. MATERIALS AND METHODS - MOE MOE non-destructively inductive proximity sensor FFT νnνn dynamic signal analyzer

29. MOR AND MOE of absolute dry samples RESULTS – MOE and MOR

30. Laboratory chamber for thermal wood modification

31. Industrial chamber for thermal wood modification

32. Silvaprodukt d.o.o., Ljubljana, Sovenia

41. The first product made from thermally modified wood, modified according to “our procedure”

42. CONCLUSIONS The best characteristics of the products made of modified wood were achieved with wood, modified at temperatures between 180 °C and 210 °C In spite of the treatment, the mechanical properties of modified wood are still appropriate for wood to be used in constructions Wood modification process can ensure appropriate resistance for diverse ways of utilisation of wooden products, especially in in wet conditions