Applied Surface Science 438 (2018) 114–126 Contents lists available at ScienceDirect Applied Surface Science journal h om epa ge: www.elsevier.com/locate/apsusc Full Length Article Surface properties of thermally treated composite wood panels Catalin Croitoru a , Cosmin Spirchez b,∗ , Aurel Lunguleasa b , Daniel Cristea c , Ionut Claudiu Roata a , Mihai Alin Pop c , Tibor Bedo c , Elena Manuela Stanciu a , Alexandru Pascu a a Transilvania University of Brasov, Materials Engineering and Welding Department, 29 Eroilor Blvd., 500036, Brasov, Romania b Transilvania University of Brasov, Wood Processing and Design of Wooden Products Department, 29 Eroilor Blvd., 500036, Brasov, Romania, c Transilvania University of Brasov, Materials Science Department, 29 Eroilor Blvd., 500036, Brasov, Romania a r t i c l e i n f o Article history: Received 3 June 2017 Received in revised form 1 August 2017 Accepted 28 August 2017 Available online 1 September 2017 Keywords: Wood panels Thermal treatment Wettability Wear resistance XPS spectroscopy FTIR spectroscopy a b s t r a c t Composite finger-jointed spruce and oak wood panels have been thermally treated under standard pres- sure and oxygen content conditions at two different temperatures, 180 ◦ C and respectively 200 ◦ C for short time periods (3 and 5 h). Due to the thermally-aided chemical restructuration of the wood components, a decrease in water uptake and volumetric swelling values with up to 45% for spruce and 35% for oak have been registered, comparing to the reference samples. In relation to water resistance, a 15% increase of the dispersive component of the surface energy has been registered for the thermal-treated spruce panels, which impedes water spreading on the surface. The thermal-treated wood presents superior resistance to accelerated UV exposure and subsequently, with up to 10% higher Brinell hardness values than refer- ence wood. The proposed thermal treatment improves the durability of the finger-jointed wood through a more economically and environmental friendly method than traditional impregnation, with minimal degradative impact on the structural components of wood. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Wood represents one of the most lightweight and sustain- able construction materials, due to its renewability, low carbon footprint, cost efficiency and ease of use [1–3]. The main disad- vantages of wood are represented by its low dimensional stability to moisture, coupled with high susceptibility to biological attack and to outdoor UV-photodegradation [4,5]. Various energy inten- sive industrial processes currently employed for improving the durability of wood such as coating and/or impregnation make use of toxic monomers, resins, solvents and preservatives [6,7]. Sev- eral milder processes, with limited industrial applicability have been described up to date, such as impregnation with natural com- pounds (plant extracts, polymerizable natural unsaturated oils [8], biopolymers such as chitosan or zein [9,10]). Thermal treatment is one of the most cost-efficient and ecologic methods for wood dura- bility improvement, through which higher fungal decay and UV degradation resistance, reduced hygroscopicity, improved dimen- sional stability and surface hardness could be imparted to wood. ∗ Corresponding author. E-mail address: cosmin.spirchez@unitbv.ro (C. Spirchez). Various technological processes have been implemented over time (ThermoWood, Perdure, and so forth), employing heating wood at temperatures ranging from 160 to 260 ◦ C in different envi- ronments such as air, vacuum, nitrogen, argon, steam or oil [11–14]. Under these conditions, supplementary crosslinks could be formed between lignin molecules, or between cellulose/hemicelluloses and the extractive compounds, which stabilize the cellulose microfib- rils through interfering with their expanding and water absorption [14]. One of the most often used engineered wood products are finger joint laminated boards, which bear satisfactory mechanical resis- tance due to cross-graining, but still relatively low performances in outdoor conditions use (dimensional stability, UV radiation resis- tance) [15]. Typical softwoods (spruce, fir, pine and so forth), often used in wood engineering applications are among the least durable wood species and through thermal treatment, their biological and dimen- sional resistance are improved to resemble the properties of more expensive species [16,17]. Hardwoods, while proving more durable than softwoods, could still be made more dimensionally and chem- ically stable by the supplementary polymerization of extractives (for example tannins) and lignin in their structure [18]. Most of the studies from reference literature describe the mod- ifications in the engineering properties of thermal-treated wood https://doi.org/10.1016/j.apsusc.2017.08.193 0169-4332/© 2017 Elsevier B.V. All rights reserved.