WOOD RESEARCH Volume 64, Number 3, 2019
Sergiy Kulman, Liudmyla Boiko, Diana Hamáry Gurová, and Ján Sedliačik

Prediction the fatigue life of wood-based panels

This work presents the results of an experimental investigation of the vibration response of cyclically loaded wood-based panels. The maximum temperature of the stationary state of the activation zone of samples of wood-based panels in the form of a rigid cantilever with their cyclic load at loading frequencies from 0 to 50 Hz and maximum internal stresses from 0.98 to 5.36 MPa was investigated. The purpose of this study is to determine the temperature of selfheating and to determine the dependence of the temperature on the loading conditions. The mathematical model is proposed in the form of system nonlinear ordinary differential equations, where stress, strain and temperature were used as the essential variables. The behaviour of the system is completely determined by the ratio of the introduced external energy and the value of the order parameter. The critical value of the order parameter depends on the thermo-physical properties of the material and is equal to the ratio of the value of the heat transfer coefficient multiplied by the area of thermal dispersion to the coefficient of linear thermal expansion.

WOOD RESEARCH Volume 64, Number 3, 2019
SHAOXIANG CAI, Naihua Zhang, Kang Li, YANJUN LI, and Xinzhou Wang

Effect of pressurized hot water treatment on the mechanical properties, surface color, chemical composition and crystallinity of pine wood

The effect of a pressurized hot water treatment (PHWT) on the mechanical properties, chemical composition, surface color, and cellulose crystalline structure of Pine wood were examined in this study. The effects of PHWT of pine wood at 140, 160, 180, and 200°C for 1, 3 and 5 h were investigated in terms of changes in mechanical properties, chemical composition, surface color and cellulose crystallinity of pine wood by means of a GB/T standard, NREL LAP, Color Difference Meter, and X-ray diffraction (XRD). Both the temperature and treatment time showed significant effects. The results showed that the bending strength and elastic modulus decreased with an increasing temperature and duration. Changes in the chemical components and surface color occurred because of the degradation of the cellulose, hemicelluloses and lignin in the wood during the PHWT. Additionally, the relative degree of relative crystallinity of the samples increased. These findings demonstrated the potential of PHWT for the wood modification.

WOOD RESEARCH Volume 64, Number 3, 2019
Endre Magoss, Zsolt Molnár, Veronika Suri, and Ingrid Fuchs

Evaluating of wetting-induced effects on the surface stability of sanded wood

A sanding is a common woodworking operation to smooth the surface prior to apply surface finish or coating materials. All cutting processes damage the upper layer of wood surface and sanding also creates a deformation zone. This deformation zone is sensitive to artificial or environmental actions, especially to wetting. In order to determine the effect of wetting on the surface properties, to get insight into the dynamics of surface movement as a function of time during the wetting, special 3D surface roughness measurements were carried out and evaluated. For sanding of samples the most common grit sizes were selected and P100 and P180 sand papers were used. Measuring the weight of the samples the dynamics of evaporation of the applied water was also determined. The surface modification after wetting is caused by moisture gradients in the upper layer associated with swelling and shrinkage resulting in permanent deformations. For this layer the most characteristic roughness parameters are the average roughness Sa and the Abbott parameters Spk, Sk and Svk. The extent of roughness variation due to wetting is characterised by the ratio of roughness after wetting to the initial roughness value. The measurement results have shown that the simultaneous infiltration and evaporation rate has a definite influence on the surface roughness modification. The most stable wood species with the least modification were the ring-porous species, following by the diffuse-porous and conifers species. The evaporation rate measured followed the same sequence for wood species investigated.

WOOD RESEARCH Volume 64, Number 3, 2019
RIZKI ARISANDI, Sri Nugroho Marsoem, GANIS LUKMANDARU, Tatsuya Ashitani, and Koetsu Takahashi

The contents of phenolics and cell wall component of Eucalyptus pellita F. Muell stemwood and bark

Eucalyptus pellita is the fast-growing species which is being developed for a raw material of pulp and paper in Indonesia. The aim of this research was to evaluate the total phenolics (TPC) and flavanols contents (TFC) in the stemwood and bark parts from four individual trees. Another purpose was to determine its cell wall contents. Wood and bark materials in two vertical positions (bottom and top) were successively extracted using dichloromethane, ethanol and hot water as the solvents. Axial factor affected significantly in the values of hot water extract, TPC, and TFC but no significantly affected the cell wall component contents. The ethanol extract levels in the heartwood part was the significantly highest. It is noticed that the heartwood part had high levels of the TPC and TFC and low level in lignin content. From this experiment, the comparatively high levels of TPC and TFC in the heartwood indicate the potential antioxidative properties that should be explored in the future. Further, the low content of Klason lignin in the heartwood part would be an advantage for pulp production.

WOOD RESEARCH Volume 64, Number 3, 2019
Liangfei Gong, Qingming Zhang, Haozhe Liang, Siyuan Ren, and Jie Wang

Mechanical properties and microstructure of Zabelia biflora

Zabelia biflora, a kind of broad-leaved shrub, with six distinct longitudinal furrows and petal-like structure in cross section, belongs to Zabelia and consists of sections interlaced with each other. It is meaningful to focus on the peculiar appearance of Zabelia biflora for the sake of outstanding structures. On the basis of quasi-static experiments of stretching, compression along the grain direction and bending in the tangential direction, dynamic experiments of the wood over its water contents ranging from 9% to 22% have been investigated using the split Hopkinson pressure bar. Combined with the electron scanning, 3D X-ray scanning reveals the microstructure of Zabelia biflora. Results show that the maximum bending force of this wood on the joint is higher than that of wood without the joint. Besides, although the static mechanical parameters of Zabelia biflora are basically the same order of magnitude compared with other hardwoods, the bending strength of the specimen with a joint is significantly improved by contrast with the wood possessing a similar density with it. In addition, it is been proved that there is a symmetrical and glass-like density distribution in the center of the wood. Meanwhile, the density presents a gradient-layer distribution from the up-down view. The dynamic compression strength of the wood will decrease when the water content ascends at every strain rate. When the strain rate is relatively low, the compression strength will rise abruptly with the descent of the moisture content below the fiber saturation point, otherwise, this enhancement will be slower. Moreover, the strain rate exerts a reinforcement effect on the compression strength. It is not until the strain rate exceeds 1000 s-1 that there will be a sudden drop in the stress after the first arrival of the compression strength. The influence of the moisture content on dynamic platform stress of material matters only under low strain rates. Once the moisture content is higher than the fiber saturation point, this effect will also disappear.

WOOD RESEARCH Volume 64, Number 3, 2019
Pažitný Andrej, ALBERT RUSS, Boháček Štefan, Monika Stankovská, VLADIMÍR IHNÁT, and Štefan Šutý

Various lignocellulosic raw materials pretreatment processes utilizable for increasing holocellulose accessibility for hydrolytic enzymes Part II. Effect of steam explosion temperature on beech enzymatic hydrolysis

Beech wood is one of the most abundant species and the most harvested hardwood in Slovak Republic. The structure and chemical composition predetermines beech wood for the second generation bioethanol production. Steam explosion of beech wood from industrial treatment was investigated as a suitable pretreatment method. The effect of steam explosion temperature on beech sawdust enzymatic hydrolysis was investigated. Optimum steam explosion temperature at around 180°C was determined based on concentration of monosaccharides in hydrolysates and concentration of enzymatic hydrolysis inhibitors such as formic acid and acetic acid from beech sawdust. This corresponds to creating conditions resulting in good disintegration to the lignocellulosic structure which leads to increased cellulose accessibility. Non-treated beech sawdust does not enable sufficient cellulose accessibility while excessively high temperature results in significant breakdown of monosaccharides and lignin and formation of inhibitors. The concentration of inhibitors was also determined for each studied steam explosion temperature. Based on steam explosion of beech sawdust, the effect of severity factors was investigated to find the optimum conditions of steam explosion pretreatment on cellulose and xylan recovery of beech wood. The obtained optimum steam explosion temperature corresponds to severity factor R0 = 3.36 (180°C, 10 minutes).

WOOD RESEARCH Volume 64, Number 3, 2019
Hung-Chi Su, Shu-Fen Tung, Chun-Ta Tzeng, and Chi-Ming Lai

Variation in the charring depth of wood studs inside wood-frame walls with time in a fire

In this study, the variation in the charring depth of wood studs inside wood-frame walls (WFWs) in a fire was investigated. First, the time variation in the surface temperature of wood studs inside WFWs was determined based on ISO 834 fire-resistance tests, and the resulting heating conditions were used in subsequent heat exposure tests. Then, wood stud specimens of four different wood species (Chinese fir, Japanese cedar, Southern pine and spruce) were each subjected to a heat exposure test in an electric furnace. The results exhibited no significant correlation between the charring depth of the wood stud specimens and the preheating density. In addition, the test data validated that the equation proposed by Sugahara can be used for predicting the charring depth of wood studs inside WFWs in a fire.

WOOD RESEARCH Volume 64, Number 3, 2019
Annamarie Velic, Maroš Soldán, Aleš Ház, Igor Šurina, and Michal Jablonský

Determination of volatile organic compounds’ emissions from wood processing

Volatile organic compounds (VOCs) have received a great deal of attention due to their high abundance during the drying process of wood particles. This is a potential environmental issue due to being low level ozone precursors. This work aimed to study the emissions of VOCs during drying in the particleboard manufacturing process. In this study, wood particles were dry and VOCs were collected using a sorption tube. The VOCs were analyzed with gas chromatographymass spectrometry to explore the effect of temperature on the composition of main components. The results indicated that α-pinene and D-limonene were the dominant components. The results also indicated that using natural gas or wood dust as a heat source did not have a major impact on the emission characteristics of VOCs.

WOOD RESEARCH Volume 64, Number 3, 2019
Liuyang Han, Xiu Zhao, Haibin Zhou, and Xiuqin Luo

Reliability analysis on compression strength property of chinese larch visually-graded dimension lumber

The reliability analysis method was investigated in this study to obtain design values of ultimate compression strength parallel to grain (UCS) of Chinese larch visually-graded dimension lumber of common size. A total of 748 lumber samples of 40 by 90 mm were tested for static full-size compression strength according to Chinese National Standards’ requirements of the reliability index. The goodness of fit for the UCS distribution of four visual grades was analyzed and the first-order second-moment reliability analysis under different load cases was performed based on all the test data. The log-normal distribution was the optimizing fitted distribution of the compression strength of Chinese larch dimension lumber. Design values of the compression strength for grades Ic, IIc, IIIc and IVc were suggested for the minimum reliability index. These design values will be recommended to the standard committee of Chinese National Standards.

WOOD RESEARCH Volume 64, Number 3, 2019
Ilker Akyüz, Nadir Ersen, Sebahattin Tiryaki, Bahadir Çağri Bayram, Kadri Cemil Akyüz, and Huseyin Peker

Modeling and comparison of bonding strength of impregnated wood material by using different methods: Artificial neural network and multiple linear regression

In this study, the effects of vacuum time, diffusion time and pressing time on the bonding strength of Larix decidua wood impregnated with Immersol-Aqua and bonded with Klebit-303 were investigated. The vacuum time, diffusion time, and pressing time were predicted by using the artificial neural network (ANN) model and multiple linear regression (MLR) methods and the results of ANN and MLR methods were compared. The highest bonding strength (7.664 N. mm-2) was achieved when the vacuum time, the diffusion time and the pressing time were 20, 60 and 60 minutes, respectively, while the lowest value (4.62 N. mm-2) was achieved when the vacuum time, the diffusion time and the pressing time were 80, 120 and 20 minutes, respectively. The model results are as follows: The MAPE value for testing phase in the ANN was 7.266 and R2 value was 0.751 whereas the MAPE value of the MLR was 9.365 and R2 value was 0.558. The ANN model has been found to have better prediction performance than the MLR model.

WOOD RESEARCH Volume 64, Number 3, 2019
LIFEN LI, Liping Yu, Zhigang Wu, and Yingcheng Hu

Delignification of poplar wood with lactic acid-based deep eutectic solvents

A process for the delignification of poplar wood using lactic acid-based deep eutectic solvents (DESs) with different hydrogen bond acceptors (choline chloride, glycine) was studied. The effect of operational parameters on the yields of the pulps and the regenerated lignins, the chemical compositions of the pulps and the delignification extent was investigated with respect to several factors, such as the types of hydrogen bond acceptor, reaction temperature and time. The maximum delignification extent of approximately 90.4% was achieved with lactic acidcholine chloride DES at 120°C for 12 h, however only about 58.4% of lignin was removed with lactic acid-glycine DES under the same reaction condition. The structural characteristics of the pulps were subsequently investigated by Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Thermogravimetric Analysis (TGA) and compared with original wood sample and microcrystalline cellulose.

WOOD RESEARCH Volume 64, Number 3, 2019
Agata Stachowiak-Wencek

Influence of the packing method of wood products on the emission of volatile organic compounds

The work presents the influence of the way of packing the furniture on the level of emissions of volatile organic compounds (VOCs) emitted from the furniture after its unpacking. The study involved oak wood samples finished with selected varnish coating (polyurethane, waterborne and waterborne UV curable coating). After preparation the samples have been packed for 15 days into selected packaging materials: corrugated cardboard, polyurethane foam and stretch film. The VOC tests were carried out by means of the chamber test method. VOCs were analyzed by gas chromatography fitted with mass spectrometry and thermal desorption. The influence of the used type of packaging material on the level of VOCs emitted from furniture items after their immediate unpacking has been observed. The highest concentration of VOCs was found in items wrapped in stretch film while the lowest concentration was found in items packed in corrugated cardboard. That trend was irrespective of the type of coating material.

WOOD RESEARCH Volume 64, Number 3, 2019
Roman Fojtík

Moisture content analysis of wooden bridges

The article deals with assessing the impact of moisture content conditions in wood mass of the wood bridges constructions on their lifespan in Central Europe. Wood moisture content as one of main factors influencing the wooden elements mechanical properties was studied on seventeen wooden bridge constructions. The dependence of temperature and relative humidity on material moisture content was observed in summer season and also in winter season. The lifespan of historical and modern wood structures was discussed as well.

WOOD RESEARCH Volume 64, Number 3, 2019
Peter Koleda, Štefan Barcík, Ľubomír Naščák, Ján Svoreň, and Jaroslava Štefková

Cutting power during lengthwise milling of thermally modified oak wood

The paper presents experimental results of cutting power of thermally modified and non-modified hardwood of Summer oak (Quercus robur) during lengthwise milling. The process of heat treatment was performed in the atmosphere of superheated steam, at temperature 210ºC. Cutting power was determined during milling of the radial surface of modified and non-modified samples. It was calculated as the difference of power consumption by a milling machine during wood machining and at idling. Several cutting regimes were tested by combining different values of rotation speed, feed speed, rake angle and constant cutting depth ae = 1 mm. The values of cutting power are approximately the same at the kinematic angle of the tool head γ = 15°, 30°; there are bigger differences for γ = 20°. The decline of cutting power in the thermally modified (210°C) oak wood machining compared to natural oak wood is 21.7% ÷ 22.2% at the cutting speed vc =40 m. s-1.

WOOD RESEARCH Volume 64, Number 3, 2019
Cosmin Spîrchez, Aurel Lunguleasa, and Liviu Gaceu

Researches on grape husk waste obtained from the winery and its use as pellets for combustion

Nowadays, there is a tendency to find new sources of biomass and to efficiently use old sources, especially to find renewable fuels. The paper aims to use grape husks resulting from the preparation of wine as pellets for combustion. Oven dry grape husk were used to be crushed and graded with the sieve of 1×1 mm in order to obtain dust for pelletizing. The pellets obtained from grape husk winery have a good density of 979 kg. m-3; a good ash content of 4.53% and a better high and low calorific value of 20.150 MJ. kg-1 and 19.850 MJ. kg-1, respectively. All over, the obtained results showed that this kind of raw material (pellets) can be use successfully when they are pelletized.

WOOD RESEARCH Volume 64, Number 3, 2019
Cornelia Rieder-Gradinger, Martin Lindemann, Alexander Milovanovic, Christian Hansmann, and Astrid Forneck

Short note: Regulation of extractives content within oak wood used for barrique production by specific variation of raw material and process parameters

In order to guarantee a maximum quality standard of oak-barrel stored wine, (barrique), the optimization of defined phenolic and non-phenolic wood compounds (e. g. whiskey lactones), which are released into the wine during storage, is necessary to enable its unique barrique taste. Numerous factors play a crucial role for the formation of these substances within wood. Besides the origin of the wood material, also storage/drying time and defined further processing parameters are responsible for its extract composition. In the present work, oak from three different sources, which had been stored/dried for different periods, was subjected to a successively increased thermal treatment (steaming, toasting). It could be shown, that especially whiskey lactones, those wood substances, which have a decisive influence on the wine-flavor, can be controlled or increased by deliberate selection of the raw material as well as processing parameters in the course of barrel production.