Dynamic mechanical analysis of dry wood: Linear viscoelastic response region and effects of minor moisture changes

Abstract

The dynamic mechanical analysis (DMA) of wood with moisture content (MC) below 1% has not yet been described. Aiming at this low MC range, the linear viscoelastic response region (LVR) of thoroughly dried wood was studied in single-cantilever bending. The LVR limit was determined as a function of grain orientation and temperature using yellow-poplar (Liriodendron tulipifera) and southern yellow pine (Pinus spp.). The LVR limit for dry wood ranged from approximately 0.03% to 0.16% strain. The LVR limit was greater for bending perpendicular to the grain than for parallel to the grain, suggesting that DMA signal quality would be better in the former case. Southern pine generally exhibited a greater LVR limit than yellow-poplar. The LVR anisotropy was greater in yellow-poplar than in southern pine. These findings suggest that detailed LVR analysis might be useful for wood analysis, or at least that regular LVR analysis is required for reliable wood DMA. The effects of wood moisture changes (between 0% and 1%) were observed in low-temperature secondary relaxations, consistent with the previous findings of others. Yellow-poplar specimens exhibited a significant storage modulus increase over a 250°C temperature range when specimen moisture increased from 0% to ∼0.7%.

Thermal transitions of the amorphous polymers in wheat straw

“…Differences in the tan δ responses (Figure 1d) are clear. The broad transitions of that peak at about 110-120 °C, as well as the transitions around 10-20 °C, are of low intensity and might be attributed to lignin secondary transitions, found by others performing DMTA on dry wood (Hatakeyama and Hatakeyama, 2010;Sugiyama et al, 1998;Sun et al, 2007). However the straw sample exhibits a broad and intense transition at about 40 °C, which is not present in case of the extracted straw and the spruce.…”

“…Specimens were removed from the climate chamber, measured in their exact dimensions and immediately fixed in the grip and cooled to -60 °C using liquid nitrogen. To obtain dry samples, the specimens were mounted in the DMTA and then heated to 150 °C and held at this temperature for 10 minutes, to ensure that the sample was as dry as possible as suggested by Sun et al (2007). The samples were subsequently cooled to -60 °C using liquid nitrogen.…”

“…In the present study we measured the thermal transitions of wheat straw using DMTA. Since the thermal transitions of wood and its components have been thoroughly investigated (Irvine 1984;Kelley et al, 1987;Salmen and Olsson, 1998;Sun et al, 2007), it is useful to compare those of straw with those of wood. To study, whether the high wax content found in wheat straw has an effect on the transitions, solvent extracted straw was investigated as well.…”

Creep Behavior of Wood Plasticized by Moisture and Temperature

“…In this study, the value of the storage modulus at a strain of 0.009% was considered as the initial value of E0 (the values of storage modulus for all wood specimens were beginning to stabilize by this time) (Jiang and Lu 2009;Kaboorani and Blanchet 2014). The point at which storage modulus was reduced by 5% was determined as the end of LVR (Sun et al 2007;Jiang and Lu 2009;Kaboorani and Blanchet 2014). The value of stress or strain at this point was determined as a critical value of stress or strain.…”

Small deformation viscoelastic and thermal behaviours of pomegranate seed pips CMC gels

“…The LVR was determined using a strain sweep at a frequency of 1 rad.s −1 where the sample was sinusoidally deformed with increasing amplitude/strain (0.001-10 % strain, 1-50 mm amplitude) (Sun et al 2007). By analyzing the results of oscillatory stress-sweep tests for all systems, the strain amplitude of 3 % (within the LVR) was chosen to apply in all experiments.…”