Elastic modulus and stress-transfer properties of tunicate cellulose whiskers
Elastic modulus and stress-transfer properties of tunicate cellulose whiskers
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DOI：
10.1021/bm049291k
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发表时间：
2005-03-01
影响因子：
6.2
通讯作者：
Eichhorn, SJ
中科院分区：
文献类型：
--
作者：
Sturcová, A;Davies, GR;Eichhorn, SJ
利用拉曼光谱和x射线衍射研究天然纤维素纤维的变形微观力学已被广泛报道。然而，很少有关于机械性能的直接测量，特别是弹性模量，在天然状态下的高结晶材料。在这里，我们报告了利用拉曼光谱技术测量被膜纤维素的弹性模量。使用四点弯曲试验对材料的分散样品进行变形，并使用特征拉曼带（位于1095 cm(-1)）的移位作为材料应力的指示。与高度定向的亚麻样品相比，平行和垂直于激光偏振方向的样品在1095 cm（-1）处的拉曼带强度变化相对较小。这表明被膜样品是一个平面内的二维随机纤维网络。利用这一结果、拉曼位移和其他材料应变的校准，表明材料的模量非常高，约为143 GPa，拉曼带宽度的缺乏被认为是由于存在纯晶体变形而没有结晶/非晶组分的影响。该样品的1095-cm（-1）拉曼峰位移的应变灵敏度为-2.4 +/- 0.2 cm(-1)/%。采用分子力学方法，结合计算机模拟和经验力场，对材料高取向链的模量进行了预测，得到的模量为145 GPa，与实验数据吻合。然而，通过使用正模分析，发现许多模的位置接近实验拉曼带的中心位置。其中一个波段被发现以2.5 cm(-1)/%的速率移动，但由于结构的复杂性，不能完全确定该波段是否代表实验结果。
Experimental deformation micromechanics of natural cellulose fibers using Raman spectroscopy and X-ray diffraction have been widely reported. However, little has been published on the direct measurements of the mechanical properties, and in particular the elastic modulus, of the highly crystalline material in the native state. Here we report on measurements of the elastic modulus of tunicate cellulose using a Raman spectroscopic technique. A dispersed sample of the material is deformed using a four-point bending test, and a shift in a characteristic Raman band (located at 1095 cm(-1)) is used as an indication of the stress in the material. Relatively little intensity change of the Raman band located at 1095 cm(-1) is shown to occur for samples oriented parallel and perpendicular to the polarization direction of the laser, as compared to a highly oriented flax sample. This indicates that the tunicate sample is a two-dimensional in-plane random network of fibers. By use of this result, the Raman shift, and calibrations with strain from other materials, it is shown that the modulus of the material is very high, at about 143 GPa, and a lack of Raman band broadening is thought to be due to the fact that there is pure crystalline deformation occurring without the effect of crystalline/amorphous fractions. A strain sensitivity of the shift in the 1095-cm(-1) Raman peak for this specimen is shown to be -2.4 +/- 0.2 cm(-1)/%. A molecular mechanics approach, using computer simulation and an empirical force field, was used to predict the modulus of a highly oriented chain of the material, and this is found to be 145 GPa, which is in agreement with the experimental data. However, by use of a normal-mode analysis, it is found that a number of modes have positions close to the central positions of the experimental Raman band. One in particular is found to shift at a rate of 2.5 cm(-1)/%, but due to the complex nature of the structure, it is not entirely conclusive that this band is representative of the experimental findings.