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This paper presents differences in the drying behavior of red oak and yellow-poplar sapwood, heartwood, and bark and their relationship with selected physical characteristics. Drying experiments were performed on samples of sapwood, heartwood, and bark of respective species at 105 °C under nitrogen conditions. In addition, physical characteristics such as green moisture content, specific gravity, volumetric shrinkage, shrinkage of the cell wall, total porosity, pore volume occupied by water, and specific pore volume were calculated. The results showed that the volumetric and cellular shrinkages of sapwood were greater than those of heartwood for both species. For red oak, the specific gravity of sapwood and heartwood was not significantly different. Additionally, the total porosity of heartwood was lower than that of sapwood in red oak. The results also indicated that yellow-poplar dried faster than red oak. Among all three components, bark dried faster than sapwood and heartwood in both species. The activation energy for sapwood drying was less than for heartwood drying. [ABSTRACT FROM AUTHOR]

This study aims to investigate the influence of thermal modification (TM) on the physical and mechanical properties of wood. For this purpose, the experimental part focused on selected influential parameters, namely temperature, residence time, and density, while the four-point bending strength is obtained as the output parameter. The obtained experimental data are stochastically modeled and compared with the model created by genetic programming (GP). The classical mathematical analysis obtained treatment parameters in relation to the maximum bending strength (T = 187 °C, t = 125 min ρ = 0.780 g/cm3) and compared with the results obtained by genetic algorithm (GA) (T = 208 °C, t = 122 min, and ρ = 0.728 g/cm3). It is possible to obtain models that describe experimental results well with stochastic modeling and evolutionary algorithms. [ABSTRACT FROM AUTHOR]

In continuation of our former study on a novel combined treatment of nitrogen–phosphorus fire retardant and thermomechanical densification on wood, this study focuses on the dynamic wettability and the bonding strength. The contact angle was measured using the sessile drop method and the surface energy was calculated according to the van Oss method. Water surface penetrating and spreading is analyzed by both the Shi and Gardner model and the droplet volume changing model. The results reveal that the combined treatment increased the surface energy, especially the acid–base component. The contact angle declined and the water droplet spread more easily on the surface. Meanwhile, the rate of relative droplet volume decreased by 32.6% because the surface layer was densified and stabilized by the combined process. Additionally, the surface possesses the lowest roughness and highest abrasion resistance on the tangential section. Thus, the bonding strength of the combined treated poplar decreased by 29.7% compared to that of untreated poplar; however, it is still 53.3% higher than that of 220 °C heat-treated wood. [ABSTRACT FROM AUTHOR]

To enhance compression stability and fire retardancy of densified wood, a new modification method i.e., combined nitrogen–phosphorus (NP) fire retardant pre-impregnation with surface thermo-mechanical densification is used to fabricate a certain thickness of functionalized surface layer on poplar. This combined treated wood is investigated via vertical density profile (VDP), and the compression stability is revealed by both soaking test and cone analysis. Results demonstrate that the combined treatment hardened the surface of wood and reformed the interface combination of the NP with the wood cell wall, thus making the surface tissue more close-grained. Fire retardancy was also enhanced; the total heat release and CO generation values decreased by 21.9% and 68.4%, respectively, when compared with that of solely NP-treated wood. Moreover, surface hardness increased by 15.8%, and the recovery of surface hardness and thickness were 56.8% and 77.2% lower than that of simply densified wood. It appears that this NP-involved thermal densification could be considered as an alternative approach to enhance both the compression stability and fire resistance of wood. [ABSTRACT FROM AUTHOR]