Department of Bioproducts and Biosystems, School of Chemical Engineering, Aalto University, P.O. Box 16300, 00076, Aalto, Finland.
Turku Centre for Biotechnology, University of Turku and Åbo Akademi University, 20520, Turku, Finland.
Sci Rep. 2019 Nov 13;9(1):16691. doi: 10.1038/s41598-019-53215-0.
Coagulation is a critical process in the assembly of cellulose nanofibrils into filaments by wet spinning; however, so far, the role of the coagulation solvent has not been systematically elucidated in this context. This work considers organic non-solvents (ethanol, acetone) and aqueous electrolyte solutions (NaCl(aq), HCl(aq), CaCl(aq)) for the coagulation of negatively charged cellulose nanofibrils via wet spinning. The associated mechanisms of coagulation with such non-solvents resulted in different spinnability, coagulation and drying time. The properties of the achieved filaments varied depending strongly on the coagulant used: filaments obtained from electrolytes (using Ca and H as counterions) demonstrated better water/moisture stability and thermomechanical properties. In contrast, the filaments formed from organic non-solvents (with Na as counterions) showed high moisture sorption and low hornification when subjected to cycles of high and low humidity (dynamic vapor sorption experiments) and swelled extensively upon immersion in water. Our observations highlight the critical role of counter-ions and non-solvents in filament formation and performance. Some of the fundamental aspects are further revealed by using quartz crystal microgravimetry with model films of nanocelluloses subjected to the respective solvent exchange.
在湿法纺丝中，纤维通过凝结过程组装成纤维素纳米纤维。然而，到目前为止，凝结溶剂在这个过程中的作用还没有被系统地阐明。本工作考虑了有机溶剂（乙醇、丙酮）和水基电解质溶液（NaCl(aq)、HCl(aq)、CaCl(aq)）作为带负电荷的纤维素纳米纤维的凝结剂，通过湿法纺丝进行凝结。与这些非溶剂相关的凝结机制导致不同的可纺性、凝结和干燥时间。所得到的纤维的性能强烈依赖于使用的凝固剂：使用 Ca 和 H 作为抗衡离子的电解质（使用 Ca 和 H 作为抗衡离子）得到的纤维表现出更好的水/水分稳定性和热机械性能。相比之下，由有机溶剂（带 Na 作为抗衡离子）形成的纤维在经历高湿度和低湿度循环（动态蒸汽吸附实验）时表现出高吸湿性和低角质化，并且在浸入水中时会剧烈膨胀。我们的观察结果强调了抗衡离子和非溶剂在纤维形成和性能中的关键作用。通过使用石英晶体微天平对纳米纤维素的模型薄膜进行相应的溶剂交换，进一步揭示了一些基本方面。
