Ponzecchi Andrea, Thybring Emil E, Digaitis Ramūnas, Fredriksson Maria, Solsona Sara Piqueras, Thygesen Lisbeth Garbrecht
Bioresource Chemistry and Technology, Department of Geoscience and Natural Resource Management, University of Copenhagen, Frederiksberg, Denmark.
Division of Building Materials, Lund University, Lund, Sweden.
Front Plant Sci. 2022 Sep 6;13:986578. doi: 10.3389/fpls.2022.986578. eCollection 2022.
Water is a key element for wood performance, as water molecules interact with the wood structure and affect important material characteristics such as mechanical properties and durability. Understanding wood-water interactions is consequently essential for all applications of wood, including the design of wood materials with improved durability by chemical modification. In this work, we used Raman micro-spectroscopy in combination with a specially designed moisture chamber to map molecular groups in wood cell walls under controlled moisture conditions in the hygroscopic range. We analyzed both untreated and chemically modified (acetylated to achieve two different spatial distributions of acetyl groups within the cell wall) Norway spruce wood. By moisture conditioning the specimens successively to 5, 50, and 95% relative humidity using deuterium oxide (DO), we localized the moisture in the cell walls as well as distinguished between hydroxyl groups accessible and inaccessible to water. The combination of Raman micro-spectroscopy with a moisturizing system with deuterium oxide allowed unprecedented mapping of wood-water interactions. The results confirm lower moisture uptake in acetylated samples, and furthermore showed that the location of moisture within the cell wall of acetylated wood is linked to the regions where acetylation is less pronounced. The study demonstrates the local effect that targeted acetylation has on moisture uptake in wood cell walls, and introduces a novel experimental set-up for simultaneously exploring sub-micron level wood chemistry and moisture in wood under hygroscopic conditions.
水是影响木材性能的关键因素，因为水分子与木材结构相互作用，会影响诸如机械性能和耐久性等重要材料特性。因此，了解木材与水的相互作用对于木材的所有应用都至关重要，包括通过化学改性设计具有更高耐久性的木材材料。在这项工作中，我们使用拉曼显微光谱技术，并结合一个专门设计的湿度室，在吸湿范围内的可控湿度条件下绘制木材细胞壁中的分子基团图谱。我们分析了未处理的以及经过化学改性（乙酰化处理以在细胞壁内实现两种不同的乙酰基空间分布）的挪威云杉木。通过使用氧化氘（DO）将样品依次调节至5%、50%和95%的相对湿度，我们确定了细胞壁中的水分位置，并区分了水可及和不可及的羟基。拉曼显微光谱技术与氧化氘保湿系统的结合实现了前所未有的木材与水相互作用图谱绘制。结果证实了乙酰化样品的吸水量较低，此外还表明，乙酰化木材细胞壁内水分的位置与乙酰化不太明显的区域有关。该研究证明了定向乙酰化对木材细胞壁吸水量的局部影响，并引入了一种新颖的实验装置，用于在吸湿条件下同时探索木材的亚微米级化学组成和水分情况。
