Modelling polymer interactions of the 'molecular Velcro' type in wood under mechanical stress
Modelling polymer interactions of the 'molecular Velcro' type in wood under mechanical stress
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DOI：
10.1016/j.jtbi.2008.03.010
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发表时间：
2008-08-07
影响因子：
2
通讯作者：
Jarvis, M. C.
中科院分区：
文献类型：
--
作者：
Altaner, C. M.;Jarvis, M. C.
树木通过合成机械性能差异很大的木材来承受风和雪荷载：小树枝和树苗的茎是柔韧的，而成熟茎的外部是刚性的。 Keckes 等人的“分子 Velcro”模型。 [2003。木材不可逆变形后细胞壁的恢复。纳特。马特。 2, 810-814] 允许模拟活树中的水饱和木材的拉伸特性。该模型的一个基本特征是附着在相邻纤维素微纤维上的半纤维素链之间存在非共价相互作用，这些半纤维素链在高于原纤维间剪切的阈值水平时被破坏。然而，其他证据并未证实半纤维素-半纤维素缔合在原纤维间基质内聚力中的重要性。在这里，我们提出了一种替代模型，其中半纤维素链从一个微纤维聚集体（宏纤维）连续桥接到下一个，提供了大部分的内聚力。我们证明了这种半纤维素桥的存在，并且在垂直于大原纤维的拉伸应力分量下，桥链从纤维素表面剥离可以为一个宏原纤维与下一个之间的剪切变形提供另一种触发机制。当一根大原纤维滑过另一根大原纤维时，木材细胞壁的一个区域可以延伸，但同时它会扭曲，直到大原纤维之间的间距再次减小，并恢复通过半纤维素桥的接触。因此，整体变形是通过一系列局部粘滑事件发生的，涉及木材细胞壁内小区域的暂时扭曲。此修改后的“分子尼龙搭扣”模型的建模负载变形曲线与原始模型的负载变形曲线相似，但不相同。然而，该机制是不同的，并且与当前对木材细胞壁结构的看法更加一致，提供了一个框架，在该框架内可以考虑在树木的不同部分合成的木材的刚性的发育控制。 (C) 2008 Elsevier Ltd. 保留所有权利。
Trees withstand wind and snow loads by synthesising wood that varies greatly in mechanical properties: flexible in twigs and in the stem of the sapling, and rigid in the outer part of the mature stem. The 'molecular Velcro' model of Keckes et al. [2003. Cell-wall recovery after irreversible deformation of wood. Nat. Mater. 2, 810-814] permits the simulation of the tensile properties of water-saturated wood as found in living trees. A basic feature of this model is the presence of non-covalent interactions between hemicellulose chains attached to adjacent cellulose microfibrils, which are disrupted above a threshold level of interfibrillar shear. However, other evidence does not confirm the importance of hemicellulose-hemicellulose association in the cohesion of the interfibrillar matrix. Here, we present an alternative model in which hemicellulose chains bridging continuously from one microfibril aggregate (macrofibril) to the next provide most of the cohesion. We show that such hemicellulose bridges exist and that the stripping of the bridging chains from the cellulose surfaces under the tensile stress component normal to the macrofibrils can provide an alternative triggering mechanism for shear deformation between one macrofibril and the next. When one macrofibril then slides past another, a domain of the wood cell wall can extend but simultaneously it twists until the spacing between macrofibrils is reduced again and contact through hemicelluloses bridges is restored. Overall deformation therefore takes place through a series of local stick-slip events involving temporary twisting of small domains within the wood cell wall. Modelled load-deformation curves for this modified 'molecular Velcro' model are similar, although not identical, to those for the original model. However, the mechanism is different and more consistent with current views of the structure of wood cell walls, providing a framework within which the developmental control of rigidity in wood synthesised in different parts of a tree may be considered. (C) 2008 Elsevier Ltd. All rights reserved.