TEMPO-mediated Oxidation of Native Cellulose: SEC–MALLS Analysis of Water-soluble and -Insoluble Fractions in the Oxidized Products
TEMPO-mediated Oxidation of Native Cellulose: SEC–MALLS Analysis of Water-soluble and -Insoluble Fractions in the Oxidized Products
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DOI：
10.1007/s10570-004-5835-8
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发表时间：
2005-06
期刊：
影响因子：
5.7
通讯作者：
Tsuguyuki Saito;M. Yanagisawa;A. Isogai
中科院分区：
文献类型：
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作者：
Tsuguyuki Saito;M. Yanagisawa;A. Isogai
将棉绒纤维素悬浮于水中，在pH 10.5的条件下，用NaClO/NaBr/2，2，6，6-四甲基哌啶-1-氧自由基（克里思）体系氧化棉绒纤维素（TEMPO介导氧化），并根据其粒径和表观水溶性，将氧化产物通过过滤和离心分离成几个组分。主要部分（>约。80质量%的原始棉绒纤维素）是滤纸捕获的纤维，当由其制备手抄纸时，其可形成纤维间半缩醛键。尺寸排阻色谱分析与多角度激光散射检测（SEC-MALLS）的这些纤维级分溶解在0.5%氯化锂/N，N-二甲基乙酰胺（DMAc）表明，一些解聚发生在纤维素链TEMPO介导的氧化。另一方面，明显的水溶性部分（<ca.在TEMPO-氧化的棉绒纤维素中的纤维素（占初始棉绒纤维素的20质量%）由少量具有纤维素I晶体结构的胶体颗粒组成，其通过TEMPO-介导的氧化从棉绒纤维素中脱落，并且即使在使用0.45 μm膜过滤后也混合在明显的水溶性级分中。这种胶体纤维素晶体的存在下，在TEMPO-氧化的短绒纤维素的水溶性馏分带来异常双峰SEC-洗脱模式和非常大的分子量值计算从SEC-MALLS数据。真正水溶性的纤维糖醛酸和/或具有葡糖醛酸和己烯神经酸单元的过氧化化合物也存在于水溶性级分中。
Linter cellulose was suspended in water and oxidized by the NaClO/NaBr/2,2,6,6-tetramehylpiperidine-1-oxy radical (TEMPO) system at pH 10.5 (TEMPO-mediated oxidation), and the oxidized products were separated into several fractions by filtration and centrifugation, depending on their particle sizes and apparent water-solubility. The major fraction (>ca. 80 mass % of the original linter cellulose) is the filter paper-trapped fibers, which can form inter-fiber hemiacetal linkages when handsheets are prepared thereof. Size-exclusion chromatographic analysis with multi-angle laser light scattering detection (SEC–MALLS) of these fibrous fractions dissolved in 0.5% LiCl/N,N-dimethylacetamide (DMAc) showed that some depolymerization occurred on cellulose chains during the TEMPO-mediated oxidation. On the other hand, the apparently water-soluble fractions (<ca. 20 mass % of the original linter cellulose) in the TEMPO-oxidized linter cellulose consisted of small amounts of colloidal particles having the cellulose I crystal structure, which came off from linter cellulose by the TEMPO-mediated oxidation and were mixed in the apparently water-soluble fraction even after filtration using 0.45 μm membrane. The presence of such colloidal cellulose crystals in the water-soluble fractions of the TEMPO-oxidized linter cellulose brings about anomalous bimodal SEC-elution patterns and extremely large molecular-mass values calculated from the SEC–MALLS data. Truly water-soluble cellouronic acid and/or over-oxidized compounds having glucuronic acid and hexeneuronic acid units are also present in the water-soluble fractions.