Zhang Chi, Chen Mingyang, Keten Sinan, Coasne Benoit, Derome Dominique, Carmeliet Jan
Chair of Building Physics, Department of Mechanical and Process Engineering, ETH Zurich, 8092 Zurich, Switzerland.
Department of Civil and Environmental Engineering, Northwestern University, Evanston, IL 60208-3109, USA.
Sci Adv. 2021 Sep 10;7(37):eabi8919. doi: 10.1126/sciadv.abi8919. Epub 2021 Sep 8.
Despite the thousands of years of wood utilization, the mechanisms of wood hygromechanics remain barely elucidated, owing to the nanoscopic system size and highly coupled physics. This study uses molecular dynamics simulations to systematically characterize wood polymers, their mixtures, interface, and composites, yielding an unprecedented micromechanical dataset including swelling, mechanical weakening, and hydrogen bonding, over the full hydration range. The rich data reveal the mechanism of wood cell wall hygromechanics: Cellulose fiber dominates the mechanics of cell wall along the longitudinal direction. Hemicellulose glues lignin and cellulose fiber together defining the cell wall mechanics along the transverse direction, and water severely disturbs the hemicellulose-related hydrogen bonds. In contrast, lignin is rather hydration independent and serves mainly as a space filler. The moisture-induced highly anisotropic swelling and weakening of wood cell wall is governed by the interplay of cellulose reinforcement, mechanical degradation of matrix, and fiber-matrix interface.
尽管木材已被使用了数千年，但由于其纳米级的系统尺寸和高度耦合的物理特性，木材湿力学的机制仍几乎未被阐明。本研究使用分子动力学模拟系统地表征木材聚合物、它们的混合物、界面和复合材料，在整个水化范围内产生了一个前所未有的微观力学数据集，包括膨胀、力学弱化和氢键。丰富的数据揭示了木材细胞壁湿力学的机制：纤维素纤维在细胞壁沿纵向的力学中占主导地位。半纤维素将木质素和纤维素纤维粘合在一起，决定了细胞壁沿横向的力学性能，而水会严重干扰与半纤维素相关的氢键。相比之下，木质素与水化的关系不大，主要起空间填充作用。水分诱导的木材细胞壁高度各向异性的膨胀和弱化是由纤维素增强、基体的力学降解以及纤维-基体界面之间的相互作用所控制的。
