The present work aims to investigate the feasibility of oxalic acid-choline chloride deep eutectic solvent (OA-ChCl DES), which serves as a promising green solvent that utilized in the acidic deep eutectic solvent (DES) hydrolysis. Oxalic acid-choline chloride DES cellulose nanocrystal (OA-ChCl DES CNC) was isolated from the bleached DES treated pulp (BP) through the acidic DES hydrolysis using 1:1 molar ratio of OA-ChCl DES. The functional groups, crystallinity index, morphological structure, particle size, zeta potential, thermal stability and surface chemistry of the OA-ChCl DES CNC were compared with the sulphuric acid cellulose nanocrystal (SA-CNC) that prepared via sulphuric acid hydrolysis. The findings revealed the presence of negatively charged carboxyl groups on OA-ChCl DES CNC surface after the acidic DES hydrolysis. The physicochemical analyses verified that the OA-ChCl DES CNC was in nano-sized range with polydispersity index (PdI) of 0.56, indicating slightly monodispersed nanoparticles. A stable OA-ChCl DES CNC colloidal suspension with zeta potential value of −52.1 ± 5.2 mV was obtained. The OA-ChCl DES CNC outweighed the SA-CNC in term of thermal stability (288 °C) despite having a slightly lower crystallinity index (76.7%). In fact, the OA-ChCl DES CNC with a yield of 55.1% was achieved through the acidic DES hydrolysis, suggesting that the OA-ChCl DES was capable of promoting efficient cleavage of strong hydrogen bonds in BP.

Graphic abstract

中文翻译：

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漂白稻草浆中的纤维素纳米晶体：酸性深共晶溶剂与硫酸水解

本工作旨在研究草酸-胆碱氯化物深共熔溶剂（OA-ChCl DES）的可行性，该溶剂是一种有前景的绿色溶剂，可用于酸性深共熔溶剂（DES）的水解。通过使用1：1摩尔比的OA-ChCl DES进行酸性DES水解，从漂白的DES处理过的纸浆（BP）中分离出草酸-氯化胆碱DES纤维素纳米晶体（OA-ChCl DES CNC）。将OA-ChCl DES CNC的官能团，结晶度指数，形态结构，粒度，ζ电势，热稳定性和表面化学与通过硫酸水解制备的硫酸纤维素纳米晶体（SA-CNC）进行了比较。这些发现揭示了酸性DES水解后，OA-ChCl DES数控表面上存在带负电荷的羧基。物化分析证实，OA-ChCl DES CNC在纳米范围内，多分散指数（PdI）为0.56，表明纳米颗粒略微单分散。获得了稳定的OA-ChCl DES CNC胶体悬浮液，其ζ电势值为-52.1±5.2 mV。OA-ChCl DES CNC的热稳定性（288°C）胜过SA-CNC，尽管其结晶度指数略低（76.7％）。实际上，通过酸性DES水解可实现OA-ChCl DES CNC的收率达55.1％，这表明OA-ChCl DES能够促进BP中强氢键的有效裂解。获得了稳定的OA-ChCl DES CNC胶体悬浮液，其ζ电势值为-52.1±5.2 mV。OA-ChCl DES CNC的热稳定性（288°C）胜过SA-CNC，尽管其结晶度指数略低（76.7％）。实际上，通过酸性DES水解可实现OA-ChCl DES CNC的收率达55.1％，这表明OA-ChCl DES能够促进BP中强氢键的有效裂解。获得了稳定的OA-ChCl DES CNC胶体悬浮液，其ζ电势值为-52.1±5.2 mV。OA-ChCl DES CNC的热稳定性（288°C）胜过SA-CNC，尽管其结晶度指数略低（76.7％）。实际上，通过酸性DES水解可实现OA-ChCl DES CNC的收率达55.1％，这表明OA-ChCl DES能够促进BP中强氢键的有效裂解。

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