Impact of thermal modification on color and chemical changes of African padauk, merbau, mahogany, and iroko wood species

Abstract Thermal modification is an environment-friendly technology for improving various wood properties, especially the dimensional stability, decay resistance, and color homogeneity. In this work, four tropical wood species (African padauk, merbau, mahogany, and iroko) were thermally modified by the ThermoWood process. The influence of heat treatment on the color and chemical changes of wood was studied by spectrophotometry, Fourier transform infrared (FTIR) spectroscopy, and wet chemistry methods. As the temperature increased, a decrease in lightness (L*) and a simultaneous decrease in chromatic values (a*, b*) were observed, indicating darkening and browning of the wood surface. As a result of the heat treatment, the relative content of hemicelluloses decreased the most in merbau and mahogany, while the thermal stability of iroko and African padauk was higher. All examined wood species showed a strong correlation between the lightness difference value (ΔL*) and the content of hemicelluloses (r = 0.88–0.96). The FTIR spectroscopy showed that the breakdown of C═O and C═C bonds in hemicelluloses and lignin plays an important role in the formation of chromophoric structures responsible for the color changes in the wood.

[1]  Xianjun Li,et al.  Effect of temperature on color changes and mechanical properties of poplar/bismuth oxide wood alloy during warm-press forming , 2022, Journal of Wood Science.

[2]  Arthur J. Ragauskas,et al.  Nanoscale FTIR and Mechanical Mapping of Plant Cell Walls for Understanding Biomass Deconstruction , 2022, ACS Sustainable Chemistry & Engineering.

[3]  D. Sandberg,et al.  Correlation of Studies between Colour, Structure and Mechanical Properties of Commercially Produced ThermoWood® Treated Norway Spruce and Scots Pine , 2021, Forests.

[4]  H. Viana,et al.  Termite Resistance, Chemical and Mechanical Characterization of Paulownia tomentosa Wood before and after Heat Treatment , 2021, Forests.

[5]  C. Hill,et al.  Thermal modification of wood—a review: chemical changes and hygroscopicity , 2021, Journal of Materials Science.

[6]  D. Sandberg,et al.  A Review of Wood Modification Globally – Updated Findings from COST FP1407 , 2020, Interdisciplinary Perspectives on the Built Environment.

[7]  K. Candelier,et al.  A review on life cycle assessments of thermally modified wood , 2020 .

[8]  Feliz Nhacila,et al.  Effects of thermal modification on physical and mechanical properties of Mozambican Brachystegia spiciformis and Julbernardia globiflora wood , 2020, European Journal of Wood and Wood Products.

[9]  F. Kačík,et al.  The Impact of Thermal Treatment on Structural Changes of Teak and Iroko Wood Lignins , 2020, Applied Sciences.

[10]  F. Kačík,et al.  Structural Changes of Oak Wood Main Components Caused by Thermal Modification , 2020, Polymers.

[11]  J. Kúdela,et al.  Surface Properties of Beech Wood after CO2 Laser Engraving , 2020, Coatings.

[12]  V. Kučerová,et al.  Changes in chemical and optical properties of silver fir (Abies alba L.) wood due to thermal treatment , 2019, Journal of Wood Science.

[13]  F. Kačík,et al.  Color and chemical changes in teak (Tectona grandis L. f.) and meranti (Shorea spp.) wood after thermal treatment , 2019, BioResources.

[14]  Š. Barcík,et al.  Color Change of Selected Wood Species Affected by Thermal Treatment and Sanding , 2018, BioResources.

[15]  F. Kačík,et al.  Impact of thermal modification on color and chemical changes of spruce and oak wood , 2018, Journal of Wood Science.

[16]  P. H. Mitchell.  Calculating the Equilibrium Moisture Content for Wood Based on Humidity Measurements , 2017 .

[17]  F. Negro,et al.  Thermo-Vacuum Modification of Teak Wood from Fast-Growth Plantation , 2017 .

[18]  M. Timar,et al.  Color and FTIR Analysis of Chemical Changes in Beech Wood (Fagus sylvatica L.) after Light Steaming and Heat Treatment in Two Different Environments , 2016 .

[19]  J. Matsumura,et al.  Wood Density and Mechanical Properties of Pinus kesiya Royle ex Gordon in Malawi , 2016 .

[20]  Junliang Liu,et al.  Effect of Vacuum Heat Treatment on the Chemical Composition of Larch Wood , 2016 .

[21]  P. Peng,et al.  Hydrothermal degradation of hemicelluloses from triploid poplar in hot compressed water at 180–340 °C , 2016 .

[22]  B. D. Mattos,et al.  Thermochemical and physical properties of two fast-growing eucalypt woods subjected to two-step freeze–heat treatments , 2015 .

[23]  Endre Magoss,et al.  Quality of Machined Wood Surfaces , 2015 .

[24]  Danica Kačíková,et al.  Effects of thermal treatment on chemical, mechanical and colour traits in Norway spruce wood. , 2013, Bioresource technology.

[25]  A. Ragauskas,et al.  Pseudo-lignin formation and its impact on enzymatic hydrolysis. , 2012, Bioresource technology.

[26]  D. Kocaefe,et al.  Study of the degradation behavior of heat-treated jack pine (Pinus banksiana) under artificial sunlight irradiation , 2012 .

[27]  N. Stark,et al.  HEAT-INDUCED CHEMICAL AND COLOR CHANGES OF EXTRACTIVE-FREE BLACK LOCUST (ROBINIA PSEUDOACACIA) WOOD , 2012 .

[28]  N. Stark,et al.  THE EFFECT OF HEAT TREATMENT ON THE CHEMICAL AND COLOR CHANGE OF BLACK LOCUST (ROBINIA PSEUDOACACIA) WOOD FLOUR , 2012 .

[29]  M. Boonstra,et al.  Strength properties of thermally modified softwoods and its relation to polymeric structural wood constituents , 2007, Annals of Forest Science.

[30]  H. Pereira,et al.  Chemistry and ecotoxicity of heat-treated pine wood extractives , 2011, Wood Science and Technology.

[31]  G. Wegener,et al.  Chemical changes during the production of thermo-treated beech wood , 2007, Wood Science and Technology.

[32]  Derek Stewart,et al.  Estimation of wood density and chemical composition by means of diffuse reflectance mid-infrared Fourier transform (DRIFT-MIR) spectroscopy. , 2006, Journal of agricultural and food chemistry.

[33]  T. Morén,et al.  The potential of colour measurement for strength prediction of thermally treated wood , 2006, Holz als Roh- und Werkstoff.

[34]  M. Boonstra,et al.  Chemical analysis of heat treated softwoods , 2006, Holz als Roh- und Werkstoff.

[35]  O. Faix,et al.  Classification of Lignins from Different Botanical Origins by FT-IR Spectroscopy , 1991 .