Abstract Whether water sorption hysteresis exists above 75 °C and the representation of its relationship with wood softening remains unclear. In this study, sorption hysteresis at three temperature levels, namely, 75, 90 and 99.5 °C, was investigated using accurately controlled conditioning chambers using powder samples from seven wood species. The dry mass loss percentage of the samples and proper equilibrium time was evaluated by pretests to ensure reliable sorption isotherms afterwards. The dry mass loss percentage after the entire sorption isotherm running needs to be kept within 0.5% to avoid complications in determining the equilibrium time. The abrupt increase of equilibrium moisture content at high relative humidity regions and the crossover of adsorption isotherms were not observed. Hysteresis was conspicuous at 75 and 90 °C and was statistically confirmed at 99.5 °C. High sample extractives content or unnecessarily long equilibrium time would cause significant sample dry mass loss, which may suppress the desorption isotherm to an extent that leads to unjustified hysteresis disappearance. The hysteresis behavior observed in this study suggests that wood softening does not necessarily result in hysteresis disappearance, and the explanation of hysteresis progression as a function of wood softening temperature must be evaluated with care in the future.

中文翻译：

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木材中接近 100 °C 的吸水滞后

摘要 75℃以上是否存在吸水滞后现象及其与木材软化的关系尚不清楚。在这项研究中，使用来自七种木材的粉末样品，使用精确控制的调节室研究了三个温度水平下的吸附滞后，即 75、90 和 99.5 °C。通过预测试评估样品的干质量损失百分比和适当的平衡时间，以确保之后可靠的吸附等温线。整个吸附等温线运行后的干质量损失百分比需要保持在 0.5% 以内，以避免在确定平衡时间时出现复杂情况。没有观察到在高相对湿度区域平衡水分含量的突然增加和吸附等温线的交叉。滞后现象在 75 和 90 °C 时很明显，并在 99.5 °C 时被统计证实。高样品萃取物含量或不必要的长平衡时间会导致显着的样品干质量损失，这可能会抑制解吸等温线到导致不合理的滞后消失的程度。本研究中观察到的滞后行为表明，木材软化并不一定会导致滞后消失，并且未来必须仔细评估滞后进展作为木材软化温度的函数的解释。