Chen Qi, Wei Penglian, Tang Tong, Fang Changhua, Fei Benhua
Department of Biomaterials, International Centre for Bamboo and Rattan, No. 8, Futong East Street, Chaoyang District, 100102 Beijing, People's Republic of China.
SFA and Beijing Co-Built Key Laboratory of Bamboo and Rattan Science and Technology, State Forestry Administration, 100102 Beijing, People's Republic of China.
ACS Appl Bio Mater. 2020 Oct 19;3(10):7087-7094. doi: 10.1021/acsabm.0c00921. Epub 2020 Oct 5.
Weak layers in bamboo, which are prone to the generation of cracks or are the preferred routes for crack growth, govern the machining processes and applications of bamboo. Weak layers are avoided during storing but are utilized during splitting and slicing. Gaining an understanding of the weak layers is a priority that will allow for the determination of whether to avoid or utilize them. In this study, scanning electron microscopy was used to observe the weak layers at the cellular and subcellular levels. A nanoindentation instrument and a Raman microscope were used to quantitatively characterize the mechanical properties and chemical components of these weak layers. The results show that among the three types of bamboo cells, vessel cells were the most vulnerable to damage, while fiber cells were the least susceptible to damage. The weak layers at the subcellular level were compound middle lamella (CML), thin layers of cell walls, and pits. The average storage modulus values were as follows: 13.7 GPa for CML, 17.0 GPa for pits, 20.6 GPa for thin layers, and 25.3 GPa for thick layers. Compared with the thick layers, the maximum decrement of cellulose content was 51% in CML and 41% in thin layers. With the lowest cellulose content, CML was the likeliest subcellular structure in which cracks propagated. The hardness of the pits was lower than that of the adjacent non-pit areas. The mechanical properties of bamboo increased by targeted modification of the weak layers. This work demonstrates a comprehensive investigation into weak layers of bamboo and quantitatively visualizes their mechanical and chemical properties.
竹子中的薄弱层容易产生裂纹或成为裂纹扩展的首选路径，它们决定着竹子的加工工艺和应用。在储存过程中要避免薄弱层，但在劈开和切片过程中会加以利用。了解薄弱层是一个优先事项，这将有助于确定是避开还是利用它们。在本研究中，使用扫描电子显微镜在细胞和亚细胞水平观察薄弱层。使用纳米压痕仪和拉曼显微镜对这些薄弱层的力学性能和化学成分进行定量表征。结果表明，在三种类型的竹细胞中，导管细胞最易受损，而纤维细胞最不易受损。亚细胞水平的薄弱层是复合中层（CML）、细胞壁薄层和纹孔。平均储能模量值如下：CML为13.7 GPa，纹孔为17.0 GPa，薄层为20.6 GPa，厚层为25.3 GPa。与厚层相比，CML中纤维素含量的最大降幅为51%，薄层中为41%。由于纤维素含量最低，CML是裂纹最可能扩展的亚细胞结构。纹孔的硬度低于相邻的非纹孔区域。通过对薄弱层进行有针对性的改性，竹子的力学性能得到了提高。这项工作展示了对竹子薄弱层的全面研究，并定量直观地呈现了它们的力学和化学性质。
