WOOD RESEARCH Volume 67, Number 6, 2022
Peter Godovčin, Jozef Martinka, Peter Rantuch, Martina Hladová, Juraj Kopúnek, Mária Otajovičová, and Mária Zuzana Bednáriková

Impact of temperature and ultraviolet radiation on changes of colour of fir and spruce wood

This study deals with the investigation of impact of temperature and ultraviolet (UV) radiation on spruce wood (Picea abies (L.) H. Karst.) and fir wood (Abies alba Mill.) colour changes. Samples of investigated woods species were loaded by temperatures of 110, 130, and 150°C and UV radiation (with 253.7 nm wavelength and 40 W m-2 intensity) during 72, 168, 336 and 672 hours. Colour changes were evaluated in the CIE Lab colour space. The neural network for prediction of both colour coordinates and total colour difference of spruce and fir wood was trained by data regarding exposure conditions (temperature, UV radiation and time) and by obtained results. Coefficient of determination (R2) of the neural network was above 0.99 for training, validation and testing. Average colour coordinates (± standard deviation) of the spruce and fir wood before exposure were L* = 80.08 ± 3.70, a* = 7.55 ± 2.13, b* = 21.56 ± 1.79, L* = 80.46 ± 1.91, a* = 6.84 ± 0.97, and b* = 18.90 ± 1.26, resp. Total colour differences after thermal loading were in the interval from ΔEab* = 3.76 ± 1.95 (spruce wood at 110°C) to ΔEab* = 45.37±1.46 (fir wood at 150°C). Total colour differences of both wood species exposed by UV radiation were approximately in intervals from ΔEab* = 12 to 13 (after 72 h) up to ΔEab* = 16 to 20 (after 168 to 672 h). Obtained results proven that both temperature and UV radiation have significant impact on the colour changes of the investigated woods.

WOOD RESEARCH Volume 66, Number 5, 2021
Aleš Nečas, Jozef Martinka, Peter Rantuch, Igor Wachter, and Tomáš Štefko

Impact of the electric cables installation on the ignition parameters of the spruce wood surface

This study is aimed to investigate of an impact of electrical cables installed on Norway spruce (Picea abies (L.) Karst.) wood board surface on main ignition parameters (mainly critical heat flux, ignition temperature, thermal response parameter and thermal inertia). Ignition parameters have been determined by dependence of ignition times (raised to the power of -1, -1/2 and -0.547) on heat flux. Initiation times have been measured for three configurations of spruce wood boards with surface dimensions of 100 x 100 mm ± 1 mm (the first configuration: board without cables on surface, the second configuration: board with three electrical cables on surface – spacing between cables was equal to their diameter and the third configuration: board with five electrical cables – spacing between cables was equal to their diameter) at five heat fluxes (30, 35, 40, 45 and 50 kW·m-2). Obtained results proved that installation of the electrical cables on the spruce wood board surface has a significant impact on the ignition parameters. The critical heat flux (8.5 kW·m-2), apparent thermal inertia 0.20 ± 0.02 kJ2·m-4·K-2·s-1 and ignition temperature 324 ± 105°C of spruce wood board increased up to 18 ± 3 kW·m-2 (critical heat flux), 0.68 ± 0.03 kJ2·m-4·K-2·s-1 (apparent thermal inertia) and 475 ± 27°C (ignition temperature) by the installation of electrical cables on the surface of spruce wood board.

WOOD RESEARCH Volume 61, Number 6, 2016
Lenka Melzerová, Lucie Kucíková, Tomáš Janda, and Michal Šejnoha

Estimation of orthotropic mechanical properties of wood based on non-destructive testing

This paper presents a simple approach for the derivation of effective properties of wood while accounting for its inherent anisotropy. These properties are found by combining the results of structural indentation using the Pilodyn 6J testing device and analytical homogenization in the framework of an inverse approach. This approach provides first a rough estimate of a microfibril angle and subsequently yields the predictions of the effective properties of wood. While applicable to any kind of wood we adopted the proposed methodology to spruce as a typical representative of soft wood. This allows us to exploit the presented results directly in the analysis of glued laminated timber beams made of spruce wood which is a principal goal of the present research.

WOOD RESEARCH Volume 62, Number 2, 2017
Martin Sviták and Daniel Ruman

Tensile-shear strength of layered wood reinforced by carbon materials

This article deals with the influence of selected factors (wood species, used adhesive type, carbon reinforcement) on tensile-shear strength of glued layered wood. Tensile-shear strength was investigated on samples of European beech (Fagus sylvatica L.) and European spruce (Picea abies L.). The laminated wood was modified with carbon polymer or carbon fabric, and the tensile-shear strength values were compared with non-reinforced wood. Polyurethane and epoxide adhesives were used for the experiment. The highest tensile-shear strength values were found on non-reinforced beech wood glued by epoxide adhesive. As far as the tensile-shear strength concerns, each monitored factor as well as their mutual interactions were proven to be statistically significant.

WOOD RESEARCH Volume 64, Number 6, 2019
Vladimír Mašura, Balberčák Jozef, Kuňa Vladimír, and Radoslav Mikulášik

Reaction phases of the wood constituents’ degradation during kraft cooking of spruce chips

In this study, the changes of the individual constituents of wood, mainly lignin fraction, and carbohydrate fraction of partially delignified wood chips were investigated. The concentration of alkali during kraft cooking of spruce chips were characterized with respect to the time of kraft cooking, consumed alkali and also to the time-temperature variable (H-factor). The observation brought a new fact, that the extraction of lignin and degradation of the carbohydrate fraction as well as the wood residue itself, were realized in two different reaction phases: initial and residual. The power form dependences between the studied constituents of the wood during kraft cooking were interpreted in a logarithmic coordinate system by the straight line relationship.

WOOD RESEARCH Volume 65, Number 6, 2020
Jan Polednik, Jozef Martinka, Peter Rantuch, Karol Balog, Jan Skrinsky, Mateusz Wnukowski, Zdenek Lacny, and Ales Bernatik

Energy potential of the Fischer-Tropsch fuel produced from spruce wood

The Fischer-Tropsch process is a chemical reaction that enables liquid hydrocarbons to be produced from coal, natural gas, or biomass (e.g. wood). The heat of combustion and effective heat of combustion are important data for fuel used to produce energy. The usefulness of a particular fuel for society is usually evaluated on the basis of the energy returned versus the energy invested (EROI) = energy recovered/energy invested. The subject of the research was the product of a Fischer-Tropsch synthesis from a synthesis gas, which was produced through the liquefaction of sawdust from spruce wood. The synthesis took place in the reactor FIX BED at a temperature of 220 to 350°C and a pressure of 2 to 3 MPa (the hydrogen to carbon monoxide ratio was approximately 2:1). The Fischer-Tropsch fuel that was produced had a heat of combustion of 27.79 M.kg-1, effective heat of combustion 25.14 M.kg-1 and an EROI coefficient of 2.39.