Wetting-induced changes on the surface of thermally modified Scots pine and Norway spruce wood
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The process of thermal modification can increase the dimensional stability and fungal resistance of wood, thus improving its performance in outdoor applications. This paper investigates the chemical and structural changes in thermally modified and unmodified Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) wood caused by long-term soaking, with a focus on the dynamics of the timber surface properties. Fourier transform infrared spectroscopy, pH measurements and microscopy analysis were conducted in 2-week intervals for 14–20 weeks. The main chemical degradation of the wood, which was attributed to the changes in hemicelluloses and cellulose, was identified by the decreased carboxyl signal and the increased intensity of C–O stretching after soaking. The crystallinity and hygroscopicity of the wood were also affected by soaking. The pH level of the modified wood did not change markedly during soaking. However, the initially low pH values of the thermally modified wood, combined with the effect of water, probably facilitated the wood degradation processes, thus leading to an increased number of cracks and holes, especially in the outer parts of the cell walls.
The authors thank the Mikkeli University of Applied Sciences staff and the International Thermowood® Association for their technical, materials and financial contributions, as well as Dr. Jouni Hiltunen for his valuable assistance during microscopy, Dr. Ville Nissinen for his support in FTIR test, and Dr. Veikko Möttönen for his suggestions of experimental design.
- Altgen M, Militz H (2015) Effect of temperature and steam pressure during the thermal modification process. In: 8th European conference on wood modification, Helsinki, Finland, pp 226–233Google Scholar
- Esteves BM, Pereira HM (2009) Wood modification by heat treatment: a review. BioResources 4:370–404Google Scholar
- Fengel D, Wegener G (1989) Wood: chemistry, ultrastructure, reaction. Walter de Gruyter, BerlinGoogle Scholar
- Gonzalez-Peña MM, Curling SF, Hale MDC (2009) On the effect of heat on the chemical composition and dimensions of thermally modified wood. Polym Degrad Stab 94:2184–2193. https://doi.org/10.1016/j.polymdegradstab.2009.09.003 CrossRefGoogle Scholar
- Hon D, Shiraishi N (2001) Wood and cellulosic chemistry. Marcel Dekker Inc, New YorkGoogle Scholar
- Kamdem DP, Pizzi A, Guyonnet R, Jermannaud A (1999) Durability of heat-treated wood. International Research Group on Wood Preservation, Rosenheim, pp 6–11Google Scholar
- Kocaefe D, Poncsak S, Boluk Y (2008) Effect of thermal treatment on the chemical composition and mechanical properties of birch and aspen. BioResources 3:517–537Google Scholar
- Militz H (2002) Heat treatment technologies in Europe: scientific background and technological state-of-art. In: Enhancing the durability of lumber and engineered wood products, FPS/Madison US, Conference, Florida, pp 11–13Google Scholar
- Mononen K, Jääskeläinen A, Alvila L, Pakkanen TT, Vuorinen T (2005) Chemical changes in silver birch (Betula pendula) wood caused by hydrogen peroxide bleaching monitored by color measurement (CIELab) and UV-Vis, FTIR and UVRR spectroscopy. Holzforschung 59:381–388. https://doi.org/10.1515/HF.2005.063 CrossRefGoogle Scholar
- Pizzo B, Pecoraro E, Macchioni N (2013) A new method to quantitatively evaluate the chemical composition of waterlogged wood by means of attenuated total reflectance Fourier transform infrared (ATR FT-IR) measurements carried out on wet material. Appl Spectrosc 67:553–562. https://doi.org/10.1366/12-06819 CrossRefPubMedGoogle Scholar