WOOD RESEARCH Volume 68, Number 4, 2023
Dritan Ajdinaj, Holta Çota, Fakije Zejnullahu, Rrahim Sejdiu, Agron Bajraktari, and Keli Mustafaraj

Noise Emission and Quality of Surface of Thermally Modified Silver Fir Wood Planed by Horizontal Milling Machine

This study was conducted to provide information regarding to noise emission and the surface quality of silver fir wood (Abies alba Mill.) planed at different feed rates after thermal modification. Four groups of sixteen samples were prepared. One group was used as control and the others were heated at 160°C, 190°C and 220°C, at atmospheric pressure for 3 h. After, all samples were processed along the grain by a planer machine, 3 m/min and 10 m/min feed rates were applied. Noise was measured using a sound level meter, while surface roughness measurements were performed by a stylus profilometer. Higher feed rates produced noticeably higher noise emission as for natural wood as for thermally modified one. The temperature was found to have a modest positive effect on the noise reduction. The increase of temperature and feed rate affected the increase in the surface roughness of the wood. Feed rate resulted as a more significant factor on the noise emission and on the surface roughness than temperature.

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 65, Number 3, 2020
Darius Albrektas, Milda Jucienė, Vaida Dobilaitė, and Raimondas Bliūdžius

The influence of thermal modification on the resistance to water impact properties and strength of wood used in outdoor conditions

In this study the influence of thermal modification on the resistance of wood to the impact of water and mechanical properties and to compare the durability of thermally modified and coated wood products operating in wet conditions was investigated. It was found that the weight of thermally unmodified non-coated oak wood after 48 h of soaking increased on average up to ~ 15%, and the weight of coated oak wood increased up to ~ 8%. If wood was thermally modified, the weight of non-coated oak wood increased up to ~ 9%, and the weight of coated oak wood increased up to ~ 5%. After 168 h of soaking these change is about 2 times larger. In the case of pine wood compared to oak wood these change of weight after 48 h is about 2.0 – 2.4 times and after 168 h about 1.4 – 2.0 larger. It can be stated that wooden constructions intended to be used in very wet conditions should be made of thermally modified wood without coating. Thermally modified wood will have greater dimensional and shape stability. Thermal modification reduces the swell up to 1.6 times in the case of oak, more than 2 times in the case of pine.

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 2, 2019
Zhou Qiaofang, Chen Chuanfu, Zhao Xiangyu, Tu Dengyun, and Li Kaifu

The effect of thermal modification by hot pressing on the some physical and mechanical properties in rubberwood (Hevea brasiliensis)

Rubberwood (Hevea brasiliensis) was thermal modified by hot pressing in an open system at three different temperatures (170, 185, 200°C) and two different durations (1.5, 3 h), and the effect on the physical and mechanical properties was studied. Results show that the thermal modification increased the oven-dried density and decreased the EMC (equilibrium moisture content) by 7.93% and 37.15%, respectively, and the dimensions stability was improved. Hardness, bending strength, modulus of bending and compressive strength parallel to grain of modified samples basically decreased with increasing temperature and time, but they showed a meaningful increase compared to control samples. However, impacting bending and nail withdrawal resistance decreased after hot pressing and thermal treatment, and the failure of the compensation for the impairment was the rubberwood hot pressed and thermal treated in the presence of air, and the participation of oxygen provoked rapid degradation reactions during the treatment.

WOOD RESEARCH Volume 64, Number 1, 2019
Saban Kart, Ergun Baysal, Mustafa Kucuktuvek, Turkay Turkoglu, Hilmi Toker, Caglar Altay, Cihan Cibo, and Huseyin Peker

Some surface characteristics of varnished thermowood after weathering

This study was designed to investigate some surface characteristics such as glossiness and surface roughness changes of varnished thermowood after six months of weathering. Thermal modification of Scots pine (Pinus sylvestris L.) and Oriental beech (Fagus orientalis L.) wood were carried out by hot air in an oven for 1, 2, and 3 hours at 205, 215, and 225°C. After the modification process, wood specimens were varnished using a polyurethane varnish (PV) and cellulosic varnish (CV). The natural weathering process caused an increase in the surface roughness of the test specimens according to the test results. The Scots pine and Oriental beech test specimens which were heat treated and varnished gave more favorable results compared to only varnish test specimens after natural weathering in terms of surface characteristics such as surface roughness and glossiness. Generally, as the heat treatment time and temperature increase, it is observed that the surface characteristics of the Scots pine and Oriental beech wood specimens improve positively. According to the results of the tests, the samples varnished with polyurethane varnish gave better results in terms of surface roughness at the end of the natural weathering process, whereas the samples varnished with cellulosic varnish gave better results in terms of glossiness values.

WOOD RESEARCH Volume 66, Number 1, 2021
Xin You Liu, Xin Wei Tu, and Mihaela Liu

Effects of light thermal treatments on the color, hygroscopity and dimensional stability of wood

Ailanthus wood (Ailanthus desf.) was thermally treated at three different low temperatures (140, 160, 180°C) for 2 and 4 h in order to investigate the effects on wood color, hygroscopity and dimensional stability. Results indicate that mass loss increased following the treatments, while equilibrium moisture content decreased from 11.86% to 9.88% for the 180°C and 4 h treatment. Moreover, improvements in the dimension stability were observed for post-treatment samples. The thermal treatment induced color changes in the Ailanthus wood, with a significant reduction in the lightness, yet the redness and yellowness exhibited minimal changes. FITR spectra of the thermally treated wood suggest that the heat treatment resulted in the deacetylation of hemicellulose. These results help to conclude that thermal treating temperature under 160°C can improve wood dimensional stability and maintain original color.

WOOD RESEARCH Volume 66, Number 1, 2021
Zhipeng Zhu, Dengyun Tu, Ziwei Chen, Chuanfu Chen, and Qiangfang Zhou

Effect of hot pressing modification on surface properties of rubberwood (Hevea brasiliensis)

This research aims to investigate the effect of thermal modification by hot pressing on surface characteristics of rubberwood. For this purpose, rubberwood specimens were thermally modified by hot pressing in an open system at three different temperatures (170, 185, and 200°C) for two different durations (1.5 or 3 h). Based on the results, the values of chromatic aberration (ΔE), contact angle and glossiness increased, and roughness decreased with increasing temperature and enlarging duration further. Although the contact angle had increased, it was still less than 90°. This aesthetic surface of rubberwood could be retained by using transparent organic coatings. The thermally modified rubberwood with excellent performance could be used as a material for solid wood flooring, wallboard, and furniture applications.