Ionic liquid 1-butyl-3-methylimidazolium chloride (bmimCl) is a widely applied solvent for cellulose. In this work, we studied the crystallization behavior of bmimCl in the presence of cellulose, aiming at obtaining further insight into bmimCl–cellulose interactions. To induce crystallization of bmimCl, the mixtures with 3 and 5 wt % of cellulose were subjected to −25 °C for various periods of time and investigated by Fourier transform-Raman spectroscopy, wide-angle X-ray scattering, and solid-state NMR. Even though the presence of cellulose noticeably delayed the crystallization process, bmimCl still adopted the monoclinic form M0, characterized by gauche–anti conformation of the butyl chain, which was reported previously for neat bmimCl. This lack of changes in the crystal forms adopted by bmimCl at different conditions highlights its resistance toward the perturbation of its ordering behavior. Unexpectedly, ssNMR analysis revealed the presence of a 15% crystalline fraction of cellulose in the crystallized mixture, showing that bmimCl crystallization induces partial self-organization of cellulose. Furthermore, the ssNMR spectra indicated that cellulose interacts with bmimCl ring carbon atoms, implying the existence of carbohydrate–aromatic stacking interactions in this system. Finally, the impact of water contamination (0.6 and 2.9 wt %) on the bmimCl/cellulose mixtures was studied. The higher water content effectively suppressed the crystallization of bmimCl. On the other hand, the mixture containing less water eventually crystallized, which was accompanied by the macroscopic phase separation of water and recrystallization of bmimCl into the more energetically favorable orthorhombic crystal form. This highlights the important role of cellulose in the recrystallization process as without cellulose this effect was reported only for bmimCl with considerably higher water content.

中文翻译：

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纤维素溶解对1-丁基-3-甲基咪唑鎓氯化物结晶的影响，通过拉曼光谱，广角X射线散射和固态NMR研究

离子液体氯化1-丁基-3-甲基咪唑鎓盐（bmimCl）是纤维素的一种广泛应用的溶剂。在这项工作中，我们研究了在纤维素存在下bmimCl的结晶行为，旨在进一步了解bmimCl-纤维素的相互作用。为了诱导bmimCl的结晶，将含有3wt％和5wt％纤维素的混合物在-25°C下放置了不同的时间，并通过傅里叶变换拉曼光谱，广角X射线散射和固态NMR进行了研究。 。尽管纤维素的存在显着延迟了结晶过程，但bmimCl仍采用单斜晶型M0，其特征是丁基链的反正构象，以前曾报道过纯bmimCl。bmimCl在不同条件下采用的晶体形式缺乏这种变化，突显了其对扰动其有序行为的抵抗力。出乎意料的是，ssNMR分析显示结晶混合物中存在15％的纤维素结晶部分，表明bmimCl结晶诱导了纤维素的部分自组织。此外，ssNMR光谱表明纤维素与bmimCl环碳原子相互作用，这表明该系统中存在碳水化合物-芳香族堆积相互作用。最后，研究了水污染（0.6和2.9 wt％）对bmimCl /纤维素混合物的影响。较高的水含量有效地抑制了bmimCl的结晶。另一方面，含水量少的混合物最终会结晶，它伴随着水的宏观相分离和bmimCl的重结晶成能量上更有利的正交晶型。这突显了纤维素在重结晶过程中的重要作用，因为没有纤维素，仅对含水量高得多的bmimCl报道了这种作用。