COLOUR CHARACTERISTICS OF DENSIFIED AND THERMALLY POST-TREATED BEECH AND PINE WOODS

Abstract

Effect of thermo-mechanical densification and thermal post-treatment on the colour parameters (L*, a*, b* and ΔE*) of beech (Fagus oriantalis L.) and pine (Pinus sylvestris L.) wood species were investigated. Wood specimens were densified at temperatures of 100 or 150 °C and compression ratios of 20% or 40%. Then, thermal post-treatment was applied to the specimens during 2 h at 190, 200, and 210 °C to provide dimensional stability in densified specimens. The colour change of the specimens was evaluated by CIEL*a*b* colour co-ordinate systems. The results showed that, the colour of the densified specimens at higher temperature and compression ratio was more changed. The compression temperature was more effective compared to compression ratio on the colour change of specimens. After the thermal post-treatment, colour characteristics of specimens have changed significantly depending on the increase in the treatment temperature, and specimens darkened. Densification processes has little effect on colour changes of the thermally post-treated specimens. The colour of pine specimens compared with the beech specimens more affected by the densification and thermal treatment applications. Morever, the change in a* value of specimens is more evident than the change in L* or b* values.

Keywords

• Wood material,Densification,Thermal treatment,Colour change

YOĞUNLAŞTIRILMIŞ VE TERMAL İŞLEMLİ KAYIN VE ÇAM ODUNLARININ RENK ÖZELLİKLERİ

Abstract

Kayın (Fagus oriantalis L.) ve çam (Pinus sylvestris L.) odunu örneklerinin renk özellikleri (L*, a*, b* and ΔE) üzerine termo-mekanik yoğunlaştırma ve termal işlemin etkisi araştırılmıştır. Örnekler 100 °C ve 150 °C sıcaklıkta %20 ve %40 sıkıştırma oranı ile yoğunlaştırılmıştır. Daha sonra, yoğunlaştırılmış örneklerde boyutsal stabiliteyi sağlamak için 190, 200 ve 210 °C sıcaklıkta 2 saat süresince örneklere termal işlem uygulanmıştır. Örneklerin renk değişimi CIEL*a*b* renk ko-ordinat sistemine göre değerlendirilmiştir. Araştırma sonuçlarına göre, daha yüksek sıcaklıkta ve sıkıştırma oranında yoğunlaştırılmış örneklerin rengi daha fazla değişmiştir. Örneklerin renk değişiminde, sıkıştırma oranına göre sıkıştırma sıcaklığı daha çok etkilidir. Termal işlem sonrası, örneklerin renk özellikleri işlem sıcaklığındaki artışa bağlı olarak önemli ölçüde değişmiştir ve örnekler kararmıştır. Termal işlemli örneklerdeki renk değişmelerinde yoğunlaştırma işlemlerinin etkisi önemsiz bulunmuştur. Kayın örneklere göre çam örneklerin rengi yoğunlaştırma ve termal işlem uygulamalarından daha fazla etkilenmiştir. Ayrıca, örneklerin a* değerindeki değişim L* veya b* değerindeki değişimden daha belirgindir.

Keywords

• Ağaç malzeme,Yoğunlaştırma,Termal işlem,Renk değişimi

References

1. Mitani, A. and Barboutis, I., “Changes caused by heat treatment in colour and dimensional stability of beech (Fagus sylvatica L.) wood”, Drvna Ind., 65(3), 225-232, 2014.
2. Bekhta, P., Proszyk, S. and Krystofiak, T., “Colour in short-term thermo-mechanically densified veneer of various wood species”, European Journal of Wood and Wood Products, 72(6), 785-797, 2014.
3. Welzbacher, C. R., Wehsener, J., Rapp, A. O. and Haller, P., “Thermo-mechanical densification combined with thermal modification of Norway spruce (Picea abies Karst) in industrial scale - Dimensional stability and durability aspects”, Holz als Roh -und Werkstoff, 66(1), 39-49, 2008.
4. Ünsal, Ö., Candan, Z., and Korkut, S., “Wettability and roughness characteristics of modified wood boards using a hot-press”, Industrial Crops and Products, 34(3), 1455-1457, 2011.
5. İmirzi, H. Ö., Ülker, O., and Burdurlu, E., “Effect of densification temperature and some surfacing techniques on the surface roughness of densified Scots pine (Pinus sylvestris L.)”, BioResources, 9(1), 191-209, 2014.
6. Bekhta, P., Proszyk, S., Krystofiak, T., Sedliacik, J., Novak, I., and Mamonova, M., “Effects of short-term thermomechanical densification on the structure and properties of wood veneers,” Wood Material Science and Engineering, available online, 2015.
7. Pelit, H., Budakçı, M., Sönmez, A., and Burdurlu, E., “Surface roughness and brightness of scots pine (Pinus sylvestris) applied with water-based varnish after densification and heat treatment,” Journal of Wood Science, 61(6), 586-594, 2015.
8. Fang, C. H., Cloutier, A., Blanchet, P., Koubaa, A., and Mariotti, N., “Densification of wood veneers combined with oil-heat treatment. Part 1: Dimensional stability,” BioResources, 6(1), 373-385, 2011.

9. Cai, J., Yang, X., Cai, L., and Shi, S. Q., “Impact of the combination of densification and thermal modification on dimensional stability and hardness of poplar lumber,” Drying Technology, 31(10), 1107-1113, 2013.
10. Pelit, H., Sönmez, A., and Budakçı, M., “Effects of ThermoWood® process combined with thermo-mechanical densification on some physical properties of Scots pine (Pinus sylvestris L.),” BioResources, 9(3), 4552-4567, 2014.
11. Pelit, H., Budakçı, M., and Sönmez, A., “Effects of heat post-treatment on dimensional stability and water absorption behaviours of mechanically densified Uludağ fir and black poplar woods,” BioResources, 11(2), 3215-3229, 2016.
12. Dubey, M. K., Pang, S., and Walker, J., “Effect of oil heating age on colour and dimensional stability of heat treated Pinus radiata”, European Journal of Wood and Wood Products, 69(2), 255-262, 2011.
13. Hill Callum, A. S., “Wood modification, Chemical, Thermal and other Processes”, Wiley series renewable
14. Resources, School of agricultural and forest sciences, University of Wales, Bangor, 2006.
15. Bekhta, P., and Niemz, P., “Effect of high temperature on the change in color, dimensional stability and mechanical properties of spruce wood,” Holzforschung, 57, 539-546, 2003.
16. Yıldız, S., Gezer, E. D., and Yıdız, Ü. C., “Mechanical and chemical behavior of spruce wood modified by heat,” Building & Environment, 41(12), 1762-1766, 2006.
17. Korkut, S., Kök, M. S., Korkut, D. S., and Gürleyen, T., “The effects of heat treatment on technological properties in red-bud maple (Acer trautvetteri Medw.) wood,” Bioresource Technology, 99(6), 1538-1543, 2008.
18. Kocaefe, D., Poncsak, S., Boluk, Y., “Effect of thermal treatment on the chemical composition and mechanical properties of birch and aspen”, BioResources, 3(2): 517-537, 2008.
19. Tuong, V. M., and Li, J., "Effect of heat treatment on the change in color and dimensional stability of acacia hybrid wood," BioResources, 5(2), 1257-1267, 2010.
20. Huang, X., Kocaefe, D., Kocaefe, Y., Boluk, Y., and Pichette, A., “A spectrocolorimetric and chemical study on color modification of heat-treated wood during artificial weathering”, Appl Surf Sci., 258(14), 5360–5369, 2012.
21. Kamperidou, V., Barboutis, I., Vasileiou, V., “Wood is good: With knowledge and technology to a competitive forestry and wood technology sector”, In: Proceedings of the 23rd International Scientific Conference, Zagreb, Croatia, 12th October 2012 Zagreb: Faculty of Forestry, University of Zagreb, 2012. pp 59-67.
22. Toker, H., Baysal, E., Kotekli, M., Turkoglu, T. T., Kart, S., Sen, T. F., and Peker, T. H., “Surface characterıstıcs of orıental beech and scots pıne woods heat-treated above 200 °C”, Wood Research, 61(1), 43-54, 2016.
23. Ayadi, N., Lejeune, F., Charrier, F., Charrier, B., and Merlin, A., “Color stability of heat-treated wood during artificial weathering”, Holz als Roh-und Werkstoff, 61(3), 221-226, 2003.
24. Atik, C., Candan, Z., and Ünsal, Ö., “Colour characteristics of pine wood affected by thermal compressing”, Ciência Florestal, 23(2), 475-479, 2013.
25. Sönmez, A. “Preparation and coloring, finishing on woodworking I,” Gazi University, Technical Education Faculty, Ankara, 2005.
26. Budakçı, M., Sönmez, A., and Pelit, H., "The color changing effect of the moisture content of wood materials on water borne varnishes," BioResources, 7(4), 5448-5459, 2012.
27. TS 2471 (1976). “Determination of moisture content for physical and mechanical tests in wood,” Turkish Standards Institute, Ankara, Turkey.
28. Mononen, K., Alvila, L., and Pakkanen, T. T., “CIEL*a*b* measurements to determine the role of felling season, log storage and kiln drying on coloration of Silver birch wood”, Scand. J. Forest Res., 17: 179–191, 2002.
29. González-Peña, M. M., and Hale, M. D., “Colour in thermally modified wood of beech, Norway spruce and Scots pine. Part 1: Colour evolution and colour changes”, Holzforschung, 63(4), 385-393, 2009.
30. Oliver, J. R., Blakeney, A. B., and Allen, H. M., “Measurement of Flour Color in Color Space Parameters,” Cereal Chem, 69: 546-551, 1992.
31. McGuire, R. G., “Reporting of Objective Color Measurements,” HortScience, 27: 1254-1255, 1992.
32. ASTM D2244-15a (2015). “Standard practice for calculation of color tolerances and color differences from instrumentally measured color coordinates”, USA.
33. Söğütlü, C., Sönmez, A., ‘‘Color changing effect of UV rays on some local wood species treated with various shielding agents,’’ Gazi University Journal of the Faulty of Architecture and Engineering, 21(1), 151-159, 2006.
34. Militz, H., “Heat treatment of wood: European processes and their background,”In: International Research Group Wood Pre, Section 4-Processes, Nº IRG/WP 02-40241, 2002.
35. Mitsui, K., Murata, A., Kohara, M., and Tsuchikawa, S. “Colour modification of wood by light-irradiation and heat treatment,”In: Abstracts of the First European Conference on Wood Modification, 2003, Belgium.
36. Dubey, M. K., “Improvements in Stability, Durability and Mechanical Properties of Radiata Pine Wood after Heat-Treatment in a Vegetable Oil”, Ph.D. dissertation, University of Canterbury, Christchurch, New Zealand, 2010.
37. Gündüz, G., Aydemir, D., and Korkut, S. “The effect of heat treatment on some mechanical properties and color changes of Uludağ fir wood,” Drying Technology, 28(2), 249-255, 2010.
38. Aksoy, A., Deveci, M., Baysal, E., and Toker, H., “Colour and gloss changes of Scots pine after heat modification”, Wood Research, 56(3), 329-336, 2011.
39. Akgül, M., Korkut, S., “The effect of heat treatment on some chemical properties and colour in Scots pine and Uludağ fir wood”, African Journal of Biotechnology, 7(21), 2854- 2859, 2012.
40. Şahin, H. T., and Korkut S., “Surface colour changes of turkish hazelnut wood caused by heat treatment”, Journal of Advances in Biology & Biotechnology, 6(1), 2394-1081, 2016.