Jiangsu Provincial Key Lab. of Pulp and Paper Science and Technology, Nanjing Forestry University, Nanjing 210037, Jiangsu, Peoples Republic of China.
Bio-based Colloids and Materials, School of Chemical Technology, Aalto University, PO Box 16300, Aalto FIN-00076 Espoo, Finland.
Carbohydr Polym. 2016 Jun 5;143:327-35. doi: 10.1016/j.carbpol.2016.01.048. Epub 2016 Jan 25.
Polymorphic and morphological transformations of cellulosic materials are strongly associated to their properties and applications, especially in the case of emerging nanocelluloses. Related changes that take place upon treatment of cellulose nanocrystals (CNC) in alkaline conditions are studied here by XRD, TEM, AFM, and other techniques. The results indicate polymorphic transformation of CNC proceeds gradually in a certain range of alkali concentrations, i.e. from about 8% to 12.5% NaOH. In such transition alkali concentration, cellulose I and II allomorphs coexists. Such value and range of the transition concentration is strongly interdependent with the crystallite size of CNCs. In addition, it is distinctively lower than that for macroscopic fibers (12-15% NaOH). Transmission electron microscopy and particle sizing reveals that after mercerization CNCs tend to associate. Furthermore, TEMPO-oxidized mercerized CNC reveals the morphology of individual nanocrystal of the cellulose II type, which is composed of some interconnected granular structures. Overall, this work reveals how the polymorphism and morphology of individual CNC change in alkali conditions and sheds light onto the polymorphic transition from cellulose I to II.
纤维素材料的多晶型和形态转变与其性能和应用密切相关，特别是在新兴的纳米纤维素的情况下。本文通过 XRD、TEM、AFM 等技术研究了在碱性条件下处理纤维素纳米晶体 (CNC) 时发生的相关变化。结果表明，CNC 的多晶型转变在一定的碱浓度范围内逐渐进行，即在约 8%至 12.5%NaOH 的范围内。在这种过渡碱浓度下，纤维素 I 和 II 同晶型共存。这种转变浓度的值和范围与 CNC 的微晶尺寸强烈相关。此外，它明显低于宏观纤维的浓度（12-15%NaOH）。透射电子显微镜和颗粒尺寸分析表明，在丝光化后，CNC 趋于聚集。此外，TEMPO 氧化丝光化 CNC 揭示了纤维素 II 型单个纳米晶体的形态，它由一些相互连接的颗粒结构组成。总的来说，这项工作揭示了单个 CNC 在碱性条件下的多晶型和形态如何变化，并阐明了纤维素 I 到 II 的多晶型转变。
