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木材-水分关系是木材科学领域的传统经典研究内容。随着现代分析技术不断发展,木材-水分关系研究已从宏观进入到微观,从细胞水平上升到分子水平,趋向于系统化和综合性。本文首先论述木材细胞壁壁层结构与化学组分的非均匀性以及木材中水分存在状态的多样性,得出木材-水分关系研究的热点和难点是木材中水分分布以及存在状态。其次,归纳磁共振成像、计算机断层扫描成像、中子成像和振动光谱成像4种现代分析技术应用于木材中水分分布研究的最新进展,并分析这4种技术的优缺点。其中,部分最新研究进展是:属于振动光谱成像的显微红外成像技术具有6.25μm的空间分辨率,可用于木材细胞壁水分分布研究,结果证实纤维饱和点以下木材细胞壁中水分分布具有不均匀性;而同属于振动光谱成像的显微拉曼成像技术具有1μm的空间分辨率,适用于木材细胞壁不同形态区水分分布研究,结果证实在纤维饱和点以下木材次生壁中层的含水量高于细胞角隅区。再次,总结近红外光谱、磁共振、红外光谱、拉曼光谱4种分析技术应用于木材中水分存在状态研究的最新进展,并分析这4种技术的优缺点。其中,部分最新研究进展是:木材中水分吸附的主要活性位点是羟基和羰基;纤维饱和点以下木材中吸着水的存在状态为强氢键结合水、中等氢键结合水和弱氢键结合水;根据3种状态水随相对湿度的变化趋势,可将木材中水分吸附过程分为3个阶段,每个阶段所吸附水的分子结构主要为C=O…(HOH)…OH或OH…(OH_2)…OH、WATER…HOH…WATER以及四面体结构。最后,本文指出木材中水分分布及其存在状态尚有许多疑问亟待解答,应以研发更高精度、更高灵敏度的分析技术以及更可信的谱图成分分析技术为突破口,在细胞水平、分子水平上深入揭示木材-水分关系。
Wood-moisture relationships are the classic classical study in the field of wood science. With the continuous development of modern analytical techniques, the research on wood-moisture relationship has gone from macroscopic to microscopic and from cellular level to molecular level, and tends to be systematic and comprehensive. This paper first discusses the heterogeneity of the structure and chemical composition of the cell wall in wood and the diversity of moisture present in the wood. The hot and difficult issues in the study of wood-water relationship are the water distribution and the existence status of wood. Secondly, four kinds of modern analytical techniques such as magnetic resonance imaging, computed tomography imaging, neutron imaging and vibrational spectroscopic imaging are applied to the latest research progress of moisture distribution in wood, and the advantages and disadvantages of these four kinds of technologies are analyzed. Among them, some recent research progress is that the microscopic infrared imaging technology belonging to the vibrational spectrum imaging has the spatial resolution of 6.25μm and can be used for studying the moisture distribution of the wood cell wall, and the results prove that the water distribution in the cell wall of the wood below the fiber saturation point is inhomogeneous; The microscopic Raman imaging technology, which belongs to the vibrational spectrum imaging, has a spatial resolution of 1μm and is suitable for studying the water distribution in different morphological zones of the wood cell wall. The results show that the water content of the middle wall of the secondary wall of the wood below the fiber saturation point is higher than that of the cell corner Corner. Thirdly, the recent progress in the application of four kinds of analytical techniques such as near infrared spectroscopy, magnetic resonance spectroscopy, infrared spectroscopy and Raman spectroscopy in the study of moisture existing in wood was summarized, and the advantages and disadvantages of the four techniques were analyzed. Among them, some of the latest research progress is: the main active sites of moisture adsorption in wood are hydroxyl and carbonyl; the presence of sorption water in the wood below the fiber saturation point is strongly hydrogen bonding water, moderate hydrogen bonding water and weak hydrogen bonding Water; According to the trend of relative humidity in three kinds of state water, the process of moisture adsorption in wood can be divided into three stages. The molecular structure of the adsorbed water in each stage is mainly C = O ... (HOH) ... OH or OH ... (OH_2) ... OH, WATER ... HOH ... WATER and tetrahedron structures. In the end, this paper points out that there are still many questions to be answered urgently in the water distribution and the existence status of wood. It is necessary to research and develop more accurate and sensitive analytical techniques and more credible spectral component analysis techniques as the breakthrough point. At the cellular level, In-depth reveal the level of timber - water relations.