Cell-wall recovery after irreversible deformation of wood
Cell-wall recovery after irreversible deformation of wood
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DOI：
10.1038/nmat1019
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发表时间：
2003-12-01
期刊：
影响因子：
41.2
通讯作者：
Fratzl, P
中科院分区：
文献类型：
--
作者：
Keckes, J;Burgert, I;Fratzl, P
生物材料的显著力学性质在于其复杂的层次化结构和特殊的分子力学现象(1-3)。通过对骨和珍珠层的变形和断裂的研究(4-6)，表明了分子相互作用和键恢复的根本重要性。与这些矿物基材料一样，木材也是一种具有优异机械性能的复杂纳米复合材料，尽管它主要是以聚合物为基础的。然而，在木材中，细胞壁中突起的机械作用还没有完全被理解(7-9)。在这里，我们结合了单个木材细胞和木材薄片的拉伸测试和同步辐射X射线衍射分析，以区分细胞壁内的变形机制和细胞-细胞相互作用所介导的机制。我们表明，超过屈服点的拉伸变形不会恶化单个细胞或薄片的硬度。这表明存在一种主要的恢复机制，该机制在细胞壁内的纤维素微纤维之间重新形成无定形基质，保持其力学性能。这种粘滑机制非常类似于纳米级的尼龙搭扣，提供了类似于金属中移动位错所产生的“塑性响应”。我们认为，细胞基质中的分子恢复机制是控制不同类型木材组织拉伸变形的普遍现象。
The remarkable mechanical properties of biological materials reside in their complex hierarchical architecture and in specific molecular mechanistic phenomena(1-3). The fundamental importance of molecular interactions and bond recovery has been suggested by studies on deformation and fracture of bone and nacre(4-6). Like these mineral-based materials, wood also represents a complex nanocomposite with excellent mechanical performance, despite the fact that it is mainly based on polymers. In wood, however, the mechanistic contribution of processes in the cell wall is not fully understood(7-9). Here we have combined tensile tests on individual wood cells and on wood foils with simultaneous synchrotron X-ray diffraction analysis in order to separate deformation mechanisms inside the cell wall from those mediated by cell-cell interactions. We show that tensile deformation beyond the yield point does not deteriorate the stiffness of either individual cells or foils. This indicates that there is a dominant recovery mechanism that re-forms the amorphous matrix between the cellulose microfibrils within the cell wall, maintaining its mechanical properties. This stick-slip mechanism, rather like Velcro operating at the nanometre level, provides a 'plastic response' similar to that effected by moving dislocations in metals. We suggest that the molecular recovery mechanism in the cell matrix is a universal phenomenon dominating the tensile deformation of different wood tissue types.