Faculty of Textile Science and Technology, Shinshu University, Tokida 3-15-1, Ueda, Nagano Prefecture 386-8567, Japan.
Graduate School of Science and Technology, Shinshu University, Tokida 3-15-1, Ueda, Nagano Prefecture, 386-8567, Japan.
Molecules. 2014 Dec 24;20(1):169-84. doi: 10.3390/molecules20010169.
A sterically stabilized aqueous suspension of "charge-free" cellulose nanowhiskers was prepared by hydrochloric acid hydrolysis of cotton powders and subsequent surface grafting of monomethoxy poly(ethylene glycol) (mPEG). The preparation scheme included carboxylation of the terminal hydroxyl groups in mPEG via oxidation with silica gel particles carrying 2,2,6,6-tetramethyl-1-pyperidinyloxyl (TEMPO) moieties and subsequent esterification between terminal carboxyls in mPEG and surface hydroxyl groups of cellulose nanowhiskers, mediated by 1,1'-carbonyldiimidazole (CDI) in dimethyl sulfoxide or dimethylacetamide. Some of the prepared PEG-grafted samples showed remarkable flow birefringence and enhanced stability after 24 h, even in 0.1 M NaCl, suggesting successful steric stabilization by efficient mPEG grafting. Actual PEG grafting via ester linkages was confirmed by attenuated total reflectance-Fourier transform infrared spectrometry. In a typical example, the amount of grafted mPEG was estimated as ca. 0.3 g/g cellulose by two measurements, i.e., weight increase after grafting and weight loss after alkali cleavage of ester linkages. Transmission electron microscopy indicated unchanged nanowhisker morphology after mPEG grafting.
通过对棉粉进行盐酸水解，并随后对单甲氧基聚乙二醇（mPEG）进行表面接枝，制备了“无电荷”纤维素纳米纤维的空间稳定水悬浮液。该制备方案包括通过硅胶颗粒携带的 2,2,6,6-四甲基-1-哌啶氧自由基（TEMPO）部分氧化 mPEG 末端羟基，以及随后在二甲基亚砜或二甲基乙酰胺中通过 1,1'-碳酰二咪唑（CDI）将 mPEG 末端羧基与纤维素纳米纤维表面羟基进行酯化，从而对 mPEG 进行接枝。一些制备的 PEG 接枝样品在 24 小时后甚至在 0.1 M NaCl 中显示出显著的流动双折射和增强的稳定性，这表明通过有效的 mPEG 接枝成功实现了空间稳定。衰减全反射傅里叶变换红外光谱法证实了通过酯键进行的实际 PEG 接枝。在一个典型的例子中，通过两种测量方法，即接枝后的重量增加和酯键的碱裂解后的重量损失，估计接枝的 mPEG 的量约为 0.3 g/g 纤维素。透射电子显微镜表明 mPEG 接枝后纳米纤维的形态保持不变。
