The objective of this work was to provide a rapid and nondestructive imaging method for evaluating the hygroscopic behavior of thermally modified lignocellulosic materials (softwood and hardwood). The difference in the hygroscopic behavior was explained by moisture content (MC) mapping results and molecular association characteristics of absorbed water (i.e. weakly, moderately, and strongly hydrogen-bonded water molecules) with wood at various relative humidities (RH). To achieve this goal, near-infrared (NIR) spectral images in the wavelength range 1816–2130 nm (covering the combination of stretching and deformation vibrations for OH) were used to visualize MC distributions over the surface of Japanese cedar and European beech samples which had been thermally treated at different temperatures. A curve fitting method was utilized to explore changes in water-wood structure characteristics based on shifts to longer wavelength in spectral signals caused by increasing MC. The curve fitting results support the recent nuclear magnetic resonance (NMR) studies that different bound water stabilities may pool in different compartments of the wood cell wall. Furthermore, water was firmly bound to wood at low RHs and H-bonds gained mobility as the number of absorbed molecules increased. It is concluded that NIR hyperspectral imaging also has the potential to be a complementary methodology for studying the transient changes of wood-water interactions before equilibrium.

中文翻译：

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使用近红外高光谱成像（NIR-HSI）快速无损评估热改性软木和硬木样品的吸湿性变化

这项工作的目的是提供一种快速且无损的成像方法，用于评估热改性木质纤维素材料（软木和硬木）的吸湿性能。吸湿性能的差异是由水分含量（MC）测绘结果和在各种相对湿度（RH）下与木材吸收的水（即弱，中和强氢键结合的水分子）与分子的缔合特征来解释的。为了实现这一目标，使用了波长范围为1816–2130 nm（涵盖OH的拉伸和变形振动的结合）的近红外（NIR）光谱图像来可视化日本雪松和欧洲山毛榉样品表面的MC分布，已经在不同温度下进行了热处理。利用曲线拟合方法，基于MC增大引起的光谱信号向更长波长的偏移，探索水木结构特征的变化。曲线拟合结果支持了最近的核磁共振（NMR）研究，即不同的结合水稳定性可能汇集在木质细胞壁的不同隔室中。此外，在较低的相对湿度下，水与木材牢固地结合在一起，并且随着吸收分子数量的增加，氢键的迁移率也随之提高。结论是，近红外高光谱成像也有可能成为研究平衡之前木材与水相互作用的瞬态变化的一种补充方法。曲线拟合结果支持了最近的核磁共振（NMR）研究，即不同的结合水稳定性可能汇集在木质细胞壁的不同隔室中。此外，在较低的相对湿度下，水与木材牢固地结合在一起，并且随着吸收分子数量的增加，氢键的迁移率也随之提高。结论是，近红外高光谱成像也有可能成为研究平衡之前木材与水相互作用的瞬态变化的一种补充方法。曲线拟合结果支持了最近的核磁共振（NMR）研究，即不同的结合水稳定性可能汇集在木质细胞壁的不同隔室中。此外，在较低的相对湿度下，水与木材牢固地结合在一起，并且随着吸收分子数量的增加，氢键的迁移率也随之提高。结论是，近红外高光谱成像也有可能成为研究平衡之前木材与水相互作用的瞬态变化的一种补充方法。