Thermal softening properties of various wood species within an annual ring

Abstract

Dynamic mechanical analysis (DMA) measurements of water-saturated earlywood (EW) and latewood (LW) of various wood species in the temperature range from 0 to 100 °C were focused to clarify the differences in thermal softening properties within an annual ring. The following results were obtained. The peak of tanδ caused by micro-Brownian motion of lignin was observed in both EW and LW all species. For softwoods, the peak temperatures of tanδ of EW appeared at higher temperatures than those of LW. For hardwoods, in the other hand, the peak temperatures of tanδ were slightly different between EW and LW in the diffuse-porous wood, whereas the temperatures were almost the same in the ring-porous wood. It was found that the difference in peak temperature of tanδ between EW and LW varied greatly among species. The difference in peak temperature between EW and LW was relatively large for softwoods. In addition, the thermal softening properties both in the radial and tangential directions differed depending on the species, so this suggested that there was anisotropy in the thermal softening properties depending on the species.

Controlled Interlayer Binding and Healing Improve the Transverse Properties of Upcycled Disposable Waste Wood

“…This relaxation has been attributed to the movement of water by several researchers and is known to be sensitive to the moisture content. 26,27 This peak for delignified wood moved slightly to −77 °C, signifying that the removal of lignin may have increased the moisture absorption capacity of the wood. In this light, it is likely that the shift of the β peak in modified wood is related to an increase in the moisture content.…”

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

“…When the temperature increased from 30 • C to 80 • C, the decrement in tensile modulus for LT-EW, LT-LW, TL-EW, and TL-LW was 32.4%, 29.1%, 84.0%, and 76.8%, respectively. Under water-saturated conditions, heat energy is provided for the Brownian motion of polymer molecules and chain segments, resulting in the decrement in tensile modulus with the rising temperature [11,12]. Accordingly, the decrements in tensile modulus for EW were larger than those for LW in both the L and T directions.…”

“…Numerous scholars have extensively explored the differences in the tensile mechanical properties between EW and LW at a given temperature and moisture content (MC) level [6][7][8][9][10][11][12]. Roszyk [7] reported on the tensile mechanical behavior of the EW and LW of pine wood (Pinus sylvestris) in the longitudinal (L) direction in the wet and air-dry states, and found that tensile strength, modulus of elasticity, and stress at the proportionality limit of EW and LW decreased generally as the MC increased.…”

“…It is well known that wood strength decreases with temperature. The wood cell wall polymers are provided with heat energy for segmental motion, resulting in the decrement of wood stiffness [11,12]. Differences in density, microfibril angle (MFA), chemical compositions, and cell structure might be the reasons for the differences in the tensile mechanical properties of EW and LW [13][14][15][16].…”

“…Likewise, the tensile mechanical behavior of wood differs vastly in the L direction and in the transverse directions [17][18][19]. In general, previous comparative studies on the tensile mechanical behavior of EW and LW mainly focused in the L direction [7][8][9][10]; little research had been conducted on the tensile mechanical properties of EW and LW in the tangential (T) direction [12]. Horiyama et al [12] investigated the tensile dynamic mechanical properties of water-saturated EW and LW within an annual ring in the T direction in the temperature range from 20 • C to 100 • C, and found that the dynamic modulus of LW was larger than that of EW for all wood species, regardless of softwood or hardwood.…”