Effect of One-Sided Surface Charring of Beech Wood on Density Profile and Surface Wettability

Abstract

One-sided surface charred European beech wood (Fagus sylvatica L.) was studied. Radial and tangential specimens of dimensions of 50 × 25 × 350 mm were one-sided surface charred at 200, 250, 300, 350, and 400 °C for various times using a contact heating system. Specimens of dimensions of 50 × 25 × 50 mm3 were prepared for treatment intensity analysis and its effect on surface wettability. Density profiles of the radial and tangential charred specimens were determined using X-ray densitography with a resolution of 0.05 mm. The wettability of the one-sided surface charred wood specimens was analyzed via contact angle, measured using the sessile drop method and determined over 10 to 150 s. The oven-dried specimens were partially submerged in water and water uptake was recorded after 2, 4, 6, 8, 10, 48, and 72 h according to EN-927-5. The surface density of the radial specimen groups charred at 200 °C for 6 min and 250 °C for 4 min decreased by about 4.5 to 8.2%. With increasingly severe charring, the surface density decreased by about 15.5 to 33.5%. A mild charring process produced a surface charred layer of approx. 2 mm, while higher temperatures and longer times affected the density up to 4–6 mm beneath the surface. Differences were found between the water uptake of the radial and tangential charred beech specimens. The most significant decrease of 56% in water uptake was recorded for the radial group prepared at 200 °C for 20 min after floating in water for 72 h. Water uptake in the radial groups modified at 250 °C for 4 and 6 min after 72 h decreased by 38% and 36%, respectively. The tangential groups did not show any statistically significant decrease. The average water uptake of the groups charred at 200 °C for 20 min, 350 °C for 2 min and 400 °C for 1 min was greater than that of the reference; the variability of the measured data was significantly greater due to the highly anisotropic character of the tangential specimens. Micro cracks were also visible on the surface. Concluding from the results of this study, one-sided surface charred beech wood exhibits increased potential in terms of wood–water related properties when a temperature range of 200–400 °C is applied.

Evaluating the quality of surface carbonized woods modified with a contact charring or a gas flame charring technique

“…The SF group showed the highest surface roughness with R a of 143 µm. The increased surface roughness is caused by the charring process: a heterogeneous modi ed layer with variable sized cracks is formed due to the uneven action of the ame on the surface during the process (Ebner 2021), while a more homogeneous surface can be achieved by using the hot plate (Šeda et al 2021;Kymäläinen et al 2022c). However, it is necessary to use appropriate parameters of the modi cation process.…”

Artificial Weathering of Contact-Charred Wood—The Effect of Modification Duration, Wood Species and Material Density

“…In the process, the wood is pressed against a heated surface for a given modification time. The process is not commercialized, but recent laboratory-scale studies have given insights into improved sorption properties and wettability characteristics [ 11 , 12 , 13 , 14 ] and changes in chemical composition and functional groups toward a more stable material [ 13 , 15 , 16 ]. Mechanical performance was found to improve in terms of modulus of rupture [ 13 ], but dimensional stability in moisture exposure was not promising [ 10 , 12 , 16 ].…”

Decay Resistance of Surface Carbonized Wood

“…The techniques include the traditional “free” flame charring, where the boards are set on fire by ignition flame [ 3 , 4 ], and the more controlled gas flame charring, where boards are either charred by a handheld torch or conveyed beneath static torches [ 5 , 6 , 7 ]. Not yet commercialized, the contact charring technique relies on the use of a heated plate in tight contact with the modified wood surface, providing a highly repeatable and controlled result [ 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ].…”