Surface peeling of cellulose nanocrystals resulting from periodate oxidation and reductive amination with water-soluble polymers
Surface peeling of cellulose nanocrystals resulting from periodate oxidation and reductive amination with water-soluble polymers
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DOI：
10.1007/s10570-015-0785-x
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发表时间：
2015-12-01
期刊：
影响因子：
5.7
通讯作者：
Jean, Bruno
中科院分区：
文献类型：
--
作者：
Azzam, Firas;Galliot, Magali;Jean, Bruno
首先对纤维素纳米晶体（CNC）进行高碘酸盐氧化以增加反应时间，然后用水溶性胺封端聚合物进行还原胺化。通过成像 (TEM)、光谱（FTIR 和 C-13 固态 NMR）和散射技术（DLS 和 WAXS）对样品的形态和化学性质进行了表征。数据显示，CNC 的高碘酸盐氧化导致氧化度 (DO) 随着反应时间的推移而增加，并且由于与邻位羟基的相互作用，大多数产生的羰基转化为半缩醛。与纤维素微纤维的情况一样，CNC 从颗粒的表面到核心都被氧化。由于反应时间短且溶解氧含量低，CNC 的形态和结晶度略有改变。长时间的氧化导致最初横向组装的微晶分离，并且数据与由于细长纤维素纳米颗粒表面的葡萄糖基单元裂解而产生的悬挂链的存在一致。与文献数据的比较进一步表明，氧化反应主要不受结晶度的影响。值得注意的是，在用水溶性聚合物链进行还原胺化后，回收了薄的未氧化的结晶纤维素纳米颗粒。这种情况似乎是由于表面氧化的悬链与水溶性聚合物发生反应及其随后的溶解而导致 CNC 的表面剥落。
Cellulose nanocrystals (CNCs) were first submitted to periodate oxidation for increasing reaction times and subsequently to reductive amination with water-soluble amine-terminated polymers. The morphology and chemical properties of the samples were characterized by imaging (TEM), spectroscopic (FTIR and C-13 solid-state NMR), and scattering techniques (DLS and WAXS). The data revealed that the periodate oxidation of CNCs resulted in an increase in the degree of oxidation (DO) with reaction time and that most of the created carbonyls were converted into hemiacetals as a result of their interaction with vicinal hydroxyl groups. Like in the case of cellulose microfibrils, CNCs were oxidized from the surface to the core of the particles. For low reaction times and concomitant low DOs, the morphology and crystallinity of the CNCs were mildly altered. A prolonged oxidation resulted in the separation of the originally laterally assembled crystallites and the data are consistent with the presence of dangling chains resulting from the cleavage of glucosyl units at the surface of the thin elongated cellulose nanoparticles. A comparison with literature data further showed that the oxidation reaction was not primarily governed by the degree of crystallinity. Remarkably, after reductive amination with water-soluble polymer chains, thin unoxidized crystalline cellulose nanoparticles were recovered. This situation seems to result from the surface peeling of the CNCs due to reaction of surface-oxidized dangling chains with water-soluble polymers and their subsequent solubilization.