Micro-tensile behavior of Scots pine sapwood after heat treatments in superheated steam or pressurized hot water

Abstract

Heat treatments reduce the strength and ductility of wood, but the extent depends on the direction of load and the treatment conditions applied. The tensile behavior of wood is very sensitive to heat treatments, but there is a lack of understanding how this is related to different heat treatment conditions. In this study, we treated homogeneous micro-veneers under different time-, temperature-, and moisture-environments and compared the effect on the tensile behavior of the treated veneers based on their chemical composition changes. The results confirmed the adverse effect of the preferential hemicellulose removal on the strength and toughness of wood. However, chemical composition changes could not fully explain the tensile behavior of dry heat-treated wood, which showed an additional loss in maximum load and work in traction at the same residual hemicellulose content compared to wet heat-treated wood. The scission of cellulose chains as well as the enhanced cross-linking of the cell wall matrix under dry heat conditions and elevated temperatures was discussed as additional factors. The enhanced cross-linking of the cell wall matrix helped in preserving the tensile properties when testing the veneers in water-saturated state, but may have also promoted the formation of cracks that propagated across the cell wall during tensile loading.

Effect of Ionic Liquid [emim][OAc] on the Set Recovery Behavior of Densified Wood

“…Especially, this degradation is further corroborated by the observed reduction in absorbance at 1740 cm -1 in both DW_1 and DW_1w (Fig. 5b, encompassing the range from 1800 to 600 cm -1 ), addressing the cleavage of acetyl groups from hemicellulose (Altgen et al 2020). Therefore, the observed results indicate the current IL treatment in wood densification does not induce cellulose degradation.…”

Comparative Studies on Tensile Mechanical Properties of Water-Saturated Earlywood and Latewood within the Same Growth Ring from Masson Pine

“…In addition, the decrements in the tensile strength of the L specimens were significantly lower than that of the T specimens. The cellulose microfibrils dominating the tensile strength of the L specimens are more stable and resistant to heat than the matrix, which is more pliable and sensitive to temperature in the hydrothermal environment [32,33], accounting for the larger values of the decrement in tensile strength of the T specimens. Furthermore, with the increase in temperature from 30 • C to 80 • C, the tensile strength of LT-EW, LT-LW, TL-EW, and TL-LW decreased by 20.76%, 16.39%, 52.02%, and 49.46%, respectively.…”

“…The cellulose microfibrils dominated the tensile modulus of the L specimens, while the matrix of lignin and hemicelluloses played the more dominating role for the tensile modulus of the T specimens [31]. The cellulose microfibrils are more stable and resistant to heat than the matrix, which is more pliable and sensitive to temperature in the hydrothermal environment [32,33], accounting for the larger values of the decrement in the tensile modulus of the T specimens.…”

“…The cellulose microfibrils dominated the tensile modulus of the L specimens, while the matrix of lignin and hemicelluloses played the more dominating role for the tensile modulus of the T specimens [31]. The cellulose microfibrils are more stable and resistant to heat than the matrix, which is more pliable and sensitive to temperature in the hydrothermal environment [32,33], accounting for the larger values of the decrement in the tensile modulus of the T specimens. To obtain more detailed information about the relationship between the tensile modulus and the hygrothermal temperature, the parameter of relative tensile modulus was calculated as follows: the tensile modulus at any temperature level (30~80 °C) was divided by the tensile modulus at 30 °C.…”

Review of Wood Modification and Wood Functionalization Technologies

“…The strength loss is dependent on the direction of load [188]. For example, the tensile strength parallel to the grain decreases strongly after thermal modification [188,189], while the compression strength shows a moderate decrease [190] or even increases [188]. The impact of thermal modification is often evaluated in static bending tests, which show only a small impact on the stiffness, a loss in strength, but most significantly, a brittle behavior with little plastic deformation and a strong reduction in toughness [157,191,192].…”