This study aims to reveal the diversity of thermal-softening temperatures and identify the factors that determine this temperature. To achieve this, the thermal-softening properties of the radial direction of wood were measured under water-saturated conditions for 15 softwood and 72 hardwood specimens. Wood samples were obtained from the xylarium of the Forestry and Forest Products Research Institute, Japan. A dynamic viscoelastic measurement was performed on samples with uniform heating and cooling history because the difference in cooling rate can alter in the mechanical properties of wood. The storage and loss elastic moduli increased linearly as wood density increased, regardless of the wood species. However, the thermal-softening temperature (defined in this study as the peak temperature of loss tangent) was unrelated to the density, anatomical features, species, latitude, and annual rainfall in the habitat. When the relationship between thermal-softening temperature and lignin structure was investigated, a negative correlation was observed between the thermal-softening temperature and the syringyl ratio (syringyl/(syringyl+guaiacyl)) of lignin aromatics. This indicates that the thermal-softening temperature is higher for wood species with denser lignin structures, supporting the prior research showed correlation between thermal-softening temperature and methoxyl group content of wood.

中文翻译：

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栖息地、密度、木质素结构和提取处理对水膨胀木材热软化特性的影响：对 87 个木材标本的研究

本研究旨在揭示热软化温度的多样性并确定决定该温度的因素。为了实现这一目标，我们在水饱和条件下测量了 15 个软木样本和 72 个硬木样本的木材径向热软化特性。木材样品取自日本林业和林产研究所的木材储藏室。对具有均匀加热和冷却历史的样品进行动态粘弹性测量，因为冷却速率的差异会改变木材的机械性能。无论木材种类如何，储存弹性模量和损耗弹性模量随着木材密度的增加而线性增加。然而，热软化温度（本研究中定义为损耗角正切峰值温度）与栖息地的密度、解剖特征、物种、纬度和年降雨量无关。当研究热软化温度与木质素结构之间的关系时，观察到热软化温度与木质素芳族化合物的紫丁香基比率(紫丁香基/(紫丁香基+愈创木基))之间呈负相关。这表明木质素结构较致密的木材树种的热软化温度较高，支持了先前研究表明木材的热软化温度与甲氧基含量之间的相关性。