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Janka hardness values according to HT schedules (temperature, ºC: time, min). C: control. Different letters mean a significant difference (p < 0.05).
Source publication
Aim of study: To evaluate the effect of heat treatment (HT) on hardness, density and color of Populus × canadensis ´I-214´ (poplar) wood.
Area of study: 15-years-old poplar wood from Pomona, Río Negro, Argentina.
Material and methods: 352 samples were exposed to different HT schedules: 120ºC, 160ºC, 180ºC and 200°C for 45 min, 90 min, 135 min and...
Contexts in source publication
Context 1
... or decrease in hardness depends on the temperature:time combination. Fig. 1 shows a tendency to a decrease in hardness with higher temperatures (180°C: light blue, 200°C: pink) in comparison with control (purple ...
Context 2
... shown in Fig. 1 and Table 2, the best hardness value was obtained at 160°C: 45 min (220.21 kg/cm 2 ), showing a significant increase of 14.34% as regards control. Moreover, at 160°C: 90 min hardness increased significantly (210.09 kg/cm 2 ) by 9.08% as compared with control. In contrast, the 180ºC: 90 min, 135ºC: 180 min 200ºC: 45 min schedules showed ...
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In this study, a modification combining densification and heat treatment of poplar wood (Populus tomentosa Carr.) was carried out, and the machining properties of theunmodified poplar wood (control) and the heat treated densified wood (HTD)were tested and evaluated. Inaddition, the water-based UV paint was covered on the control and HTD respectivel...
Citations
... A number of studies on thermal and charring treatments of wood showed decreases in wood densities due to chemical modifications in the wood (Metsä-Kortelainen et al. 2006;Boonstra et al. 2007;Gündüz et al. 2008;Akyildiz et al. 2009;Gunduz et al. 2009;Won et al. 2012;Percin et al. 2016;Antons et al. 2018;Kapidani et al. 2019;Chotikhun et al. 2020;Wang et al. 2020;Esteves et al. 2021;Gennari et al. 2021;Ninane et al. 2021;Šeda et al. 2021;Taraborelli et al. 2022). Hill et al. (2021) showed that thermal treatments for heat-modified wood generally resulted in increased mass loss and decreased wood density due to chemical degradation and that weight loss after heat treatment was generally linked to a reduction in density associated with treatment conditions and wood species (Pfriem et al. 2009). ...
Physical and mechanical properties were evaluated for all-sided charred Pinus taeda and Eucalyptus bosistoana wood by hot plate contact heating system followed by treatment with linseed oil. The water absorption, volumetric swelling, wettability, hardness, modulus of rupture, and modulus of elasticity in bending strength and compression strength parallel to grain were determined. The water absorption and volumetric swell were determined after immersion in water, as measured at various intervals of water immersion up to 120 h. The results suggested that the contact charring process with the addition of a linseed oil application improved water absorption and volumetric swell properties of charred specimens compared to un-charred controls. Hardness of the charred wood decreased by 38% and 43% in P. taeda and E. bosistoana specimens, respectively, compared with their respective controls. The highest reductions were seen in modulus of elasticity and compression strength values in charred P. taeda specimens, while modulus of rupture (MOR) values decreased more in charred E. bosistoana specimens than in charred P. taeda specimens. These results suggested that charring of P. taeda and E. bosistoana wood does improve the moisture-related characteristics; however, their mechanical behavior and hardness decreased.
This work examines the effect of thermal modification temperature (180, 200, and 220 °C) in comparison with reference (untreated) samples on selected optical properties of six tropical wood species—Sp. cedar (Cedrala odorata), iroko (Chlorophora excelsa), merbau (Intsia spp.), meranti (Shorea spp.), padouk (Pterocarpus soyauxii), and teak (Tectona grandis). The main goal is to expand the existing knowledge in the field of wood thermal modification by understanding the related degradation mechanisms associated with the formation of chromophoric structures and, above all, to focus on the change in the content of extractive substances. For solid wood, the CIELAB color space parameters (L*, a*, b*, and ΔE*), yellowness (Y), ISO brightness, and UV-Vis diffuse reflectance spectra were obtained. Subsequently, these wood samples were extracted into three individual solvents (acetone, ethanol, and ethanol-toluene). The yields of the extracted compounds, their absorption spectra, and again L*, a*, b*, ΔE*, and Yi parameters were determined. With increasing temperatures, the samples lose brightness and darken, while their total color difference grows (except merbau). The highest yield of extractives (mainly phenolic compounds, glycosides, and dyes) from thermally modified samples was usually obtained using ethanol. New types of extractives (e.g., 2-furaldehyde, lactones, formic acid, some monomer derivatives of phenols, etc.) are already created around a temperature of 180 °C and may undergo condensation reactions at higher temperatures. For padouk, merbau, teak, and partially iroko modified at temperatures of 200 and 220 °C, there was a detected similarity in the intensities of their UV-Vis DR spectra at the wavelength regions corresponding to phenolic aldehydes, unsaturated ketones, quinones, stilbenes, and other conjugated carbonyl structures. Overall, a statistical assessment using PCA sorted the samples into five clusters. Cluster 3 consists of almost all samples modified at 200 and 220 °C, and in the other four, the reference and thermally modified samples at 180 °C were distributed. The yellowness of wood (Y) has a very high dependence (r = 0.972) on its brightness (L*) and the yellowness index of the extractives in acetone Yi(Ac), whose relationship was described by the equation Y = −0.0951 × Y(Ac) + 23.3485.
