Zhang Chi, Coasne Benoit, Guyer Robert, Derome Dominique, Carmeliet Jan
1Chair of Building Physics, Department of Mechanical and Process Engineering, ETH Zurich, 8093 Zurich, Switzerland.
2Laboratory for Multiscale Studies in Building Physics, Swiss Federal Laboratories for Materials Science and Technology, Ueberlandstrasse 129, 8600 Duebendorf, Switzerland.
Cellulose (Lond). 2020;27(1):89-99. doi: 10.1007/s10570-019-02808-z. Epub 2019 Oct 31.
The use of natural sustainable resources such as wood in green industrial processes is currently limited by our poor understanding of the impact of moisture on their thermodynamic and mechanical behaviors. Here, a molecular dynamics approach is used to investigate the physical response of a typical hydrophilic biopolymer in softwood hemicellulose-xylan-when subjected to moisture adsorption. A unique moisture-induced crossover is found in the thermodynamic and mechanical properties of this prototypical biopolymer with many quantities such as the heat of adsorption, heat capacity, thermal expansion and elastic moduli exhibiting a marked evolution change for a moisture content about 30 wt%. By investigating the microscopic structure of the confined water molecules and the polymer-water interfacial area, the molecular mechanism responsible for this crossover is shown to correspond to the formation of a double-layer adsorbed film along the amorphous polymeric chains. In addition to this moisture-induced crossover, many properties of the hydrated biopolymer are found to obey simple material models.
在绿色工业过程中，诸如木材等天然可持续资源的使用目前受到限制，因为我们对水分对其热力学和力学行为的影响了解不足。在此，采用分子动力学方法来研究典型亲水性生物聚合物——软木半纤维素中的木聚糖——在吸湿时的物理响应。在这种典型生物聚合物的热力学和力学性质中发现了一种独特的水分诱导转变，许多量如吸附热、热容、热膨胀和弹性模量在水分含量约为30 wt%时表现出明显的演化变化。通过研究受限水分子的微观结构和聚合物 - 水界面面积，表明导致这种转变的分子机制对应于沿无定形聚合物链形成双层吸附膜。除了这种水分诱导转变外，还发现水合生物聚合物的许多性质符合简单的材料模型。
