Susceptibility of never-dried and freeze-dried bacterial cellulose towards esterification with organic acid
Susceptibility of never-dried and freeze-dried bacterial cellulose towards esterification with organic acid
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DOI：
10.1007/s10570-012-9680-x
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发表时间：
2012-06-01
期刊：
影响因子：
5.7
通讯作者：
Bismarck, Alexander
中科院分区：
文献类型：
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作者：
Lee, Koon-Yang;Bismarck, Alexander
本文报道了（1）从未干燥的和（2）冻干的细菌纤维素（BC）对有机酸酯化的敏感性。当用己酸改性从未干燥的BC（BC是从水通过甲醇到吡啶的溶剂交换）时，发现取代度（DS）显著低于己酸改性的冻干BC。发现冷冻干燥的BC己酸酯的结晶度与纯BC和从未干燥的BC己酸酯相比显著更低。该结果，沿着高DS，表明在冻干BC的酯化过程中发生了显著的本体改性。对于从未干燥的BC己酸酯未观察到这样的结果。所有这些证据都指向这样一个事实，即与从未干燥的BC相比，冷冻干燥的BC更容易发生有机酸酯化。一些假设进行了探讨，以解释所观察到的行为，并进一步研究，以阐明我们的观察;纤维素中的残留水的效果，羟基基团的可及性和从未干燥和冷冻干燥的BC的晶体结构上的纤维素原纤维酯化的敏感性，分别。然而，对这些假设的研究提出了更多的问题，我们仍然有一个主要的问题：为什么BC纳米纤维在修饰冻干BC或从未干燥过的BC时表现不同？
The susceptibility of (1) never-dried and (2) freeze-dried bacterial cellulose (BC) towards organic acid esterification is reported in this work. When never-dried BC (BC which was solvent exchanged from water through methanol into pyridine) was modified with hexanoic acid, it was found that the degree of substitution (DS) was significantly lower than that of hexanoic acid modified freeze-dried BC. The crystallinity of freeze-dried BC hexanoate was found to be significantly lower compared to neat BC and never-dried BC hexanoate. This result, along with the high DS indicates that significant bulk modification occurred during the esterification of freeze-dried BC. Such results were not observed for never-dried BC hexanoate. All these evidence point towards to fact that freeze-dried BC was more susceptible to organic acid esterification compared to never-dried BC. A few hypotheses were explored to explain the observed behaviour and further investigated to elucidate our observation; the effect of residual water in cellulose, the accessibility of hydroxyl groups and the crystal structure of never-dried and freeze-dried BC on the susceptibility of cellulose fibrils to esterification, respectively. However, the investigation of these hypotheses raised more questions and we are still left with the main question; why do BC nanofibres behave differently when modifying freeze-dried BC or never-dried BC?.