Surface Characteristics of Poplar Wood with High-Temperature Heat Treatment: Wettability and Surface Brittleness

Abstract

The many uses of wood are greatly affected by its surface properties, which are significantly altered by heat treatment. Investigated here are the wettability and surface brittleness when treating poplar wood with heat at 160, 180, 200, and 220 °C for 2 h. Contact angles were measured by the sessile drop method, and surface free energy was calculated. Surface brittleness was expressed by hardness (HD value), roughness (Ra, Rq, Ry, and Rz values), and abrasive resistance (K value). Next, non-destructive Fourier transform near-infrared spectroscopic (FT-NIR) and X-ray photoelectron spectroscopic (XPS) measurements were employed to analyze the surface chemical changes. Scanning electron microscopy (SEM) revealed the post-heating microscopic structure. The results demonstrated that heat treatment reduces the surface wettability while increasing the surface brittleness, which becomes more apparent with increased temperature. Significant differences were determined (p < 0.05) between the surface parameters at four different temperatures. The degradation of cell wall components and the deterioration of microstructures was further expounded by FT-NIR, XPS, and SEM analyses. Furthermore, the abrasive resistance and hardness values decreased in line with the rate of weight loss (WL, %) and temperature. This indicates a strong correlation between the surface characteristics and the WL or temperature. The intensity of heat treatment appears to be predictable and easy to regulate.

Magnetic resonance imaging evidences of the impact of water sorption on hardwood capillary imbibition dynamics

“…On the other side, it can also be noticed that the maximum height of imbibition observed within the experiment duration is in the order of cm 6 ≈ Ω S . This gives and finally leads to a value of θ not larger than 70°, which is in consistency with the typical contact angle reported in the literature (De Meijer et al 2000;Wålinder and Ström 2001;Chu et al 2016).…”

Thermal modification as tool to increase hydrophobicity of veneers

“…The water contact angle value influence on the thermally modified veneer surface increase is associated with the reduction of the veneer surface hydroxyl group content decrease due to hemicelluloses decomposition and formed monosaccharides dehydration with the formation of furfural [3;21;22]. In addition, celluloses during thermal modification increase in crystallinity by degrading the amorphous part or re-crystallize it in more hydrophobic crystallise cellulose [23]. After modification the differences among the species decrease, which could be related to leaching of extractives from the wood material and also by fact that species of lower density present better stability to thermo-degradation than species of higher density [21].…”

Heat-Treated Wood as a Substrate for Coatings, Weathering of Heat-Treated Wood, and Coating Performance on Heat-Treated Wood

“…Miklečić and Jorouš-Rajković [25] also found a reduction in total surface free energy of beech wood after heat treatments and a strong reduction of the acid-base component. Chu et al [36] calculated the total surface free energy according to the OWRK (Owens-Wendt-Rabel-Kaelble) method and established that the surface energy of heat-treated poplar wood (Populus beijingensis W.Y.Hsu) decreased with increasing temperature and polar component of surface energy also decreased with increasing temperature. In contrast, Petrič et al [35] reported that the thermal modification process in vacuum of spruce wood increased the surface free energy and decreased the polarity of wood, at the modification temperature of 210°C.…”