Effects of ball milling on the structure of cotton cellulose
Effects of ball milling on the structure of cotton cellulose
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DOI：
10.1007/s10570-018-02230-x
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发表时间：
2019-01-01
期刊：
影响因子：
5.7
通讯作者：
French, Alfred D.
中科院分区：
文献类型：
--
作者：
Ling, Zhe;Wang, Tuo;French, Alfred D.
纤维素通常被描述为结晶和无定形材料的混合物。人们认为，对纤维素材料的化学、生物化学和物理性质的一般理解很大程度上取决于这些成分的比例的结果。例如，据说非晶材料更具反应性且拉伸强度较低，但全面的理解和明确的分析仍然难以捉摸。几十年来一直使用球磨来增加非晶材料的比例。目前的工作使用了 13 种技术来跟踪球磨 15、45 和 120 分钟后棉纤维（接近纯纤维素）的变化。 X射线衍射结果采用Rietveld法进行分析；本期下一篇论文中的 DNP（动态核极化）自然丰度二维 NMR 研究有助于解释本工作中的一维分析。用于 DNP 研究的模型不需要传统 NMR 模型的副晶和难以接近的微晶表面。随着纤维素去结晶，和频发生（SFG）光谱也显示出深刻的变化。光学显微镜和场发射扫描电子显微镜结果显示了颗粒尺寸的变化；通过凝胶渗透色谱法进行的分子量和羰基分析证实了化学变化。比表面积和孔径增加。傅里叶变换红外（FTIR）和拉曼光谱也显示出渐进的变化；一些提出的 FTIR 结晶度指标与我们的结果不太一致。热重分析结果表明初始水分含量逐渐增加并且稳定性有所损失。尽管这项工作增加了对纤维素通过球磨非晶化时的结构变化的理解，但仍需要继续努力来提高本文使用的同步加速器和实验室 X 射线方法之间的一致性，并提供 SFG 结果的物理解释。
Cellulose is often described as a mixture of crystalline and amorphous material. A large part of the general understanding of the chemical, biochemical and physical properties of cellulosic materials is thought to depend on the consequences of the ratio of these components. For example, amorphous materials are said to be more reactive and have less tensile strength but comprehensive understanding and definitive analysis remain elusive. Ball milling has been used for decades to increase the ratio of amorphous material. The present work used 13 techniques to follow the changes in cotton fibers (nearly pure cellulose) after ball milling for 15, 45 and 120 min. X-ray diffraction results were analyzed with the Rietveld method; DNP (dynamic nuclear polarization) natural abundance 2D NMR studies in the next paper in this issue assisted with the interpretation of the 1D analyses in the present work. A conventional NMR model's paracrystalline and inaccessible crystallite surfaces were not needed in the model used for the DNP studies. Sum frequency generation (SFG) spectroscopy also showed profound changes as the cellulose was decrystallized. Optical microscopy and field emission-scanning electron microscopy results showed the changes in particle size; molecular weight and carbonyl group analyses by gel permeation chromatography confirmed chemical changes. Specific surface areas and pore sizes increased. Fourier transform infrared (FTIR) and Raman spectroscopy also indicated progressive changes; some proposed indicators of crystallinity for FTIR were not in good agreement with our results. Thermogravimetric analysis results indicated progressive increase in initial moisture content and some loss in stability. Although understanding of structural changes as cellulose is amorphized by ball milling is increased by this work, continued effort is needed to improve agreement between the synchrotron and laboratory X-ray methods used herein and to provide physical interpretation of the SFG results.