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One-Pot Preparation of Carboxylated Cellulose Nanocrystals and Their Liquid Crystalline Behaviors
- Zhou, Lijuan, Li, Na, Shu, Jie, Liu, Yunxiao, Wang, Kuntao, Cui, Xiang, Yuan, Yuan, Ding, BeiBei, Geng, Yong, Wang, Zhaolu, Duan, Yongxin, Zhang, Jianming
- ACS sustainable chemistry & engineering 2018 v.6 no.9 pp. 12403-12410
- atomic force microscopy, carboxylation, cellulose, cost effectiveness, crystal structure, hydrolysis, liquids, manganese, nanocrystals, oxalates, oxalic acid, oxidants, polymers, potassium permanganate, pulp, reducing agents, sulfates, sulfuric acid
- Carboxylated cellulose nanocrystals (CNCs-COOH) have attracted great attention for their potential applications in reinforcing polymer materials and surface modification. Herein, we developed a low-cost approach to prepare CNCs-COOH from pulp with high yield at mild reaction conditions (50 °C, 1 wt % sulfuric acid medium) using potassium permanganate (KMnO₄) and oxalic acid (OA, H₂C₂O₄) as the oxidizing and reducing agents, respectively. The oxidant dosage in this strategy is much lower than that in a conventional TEMPO method, and the yield of CNCs-COOH can reach as high as 68.0%, with a carboxylate content of 1.58 mmol/g. In this reaction system, the presence of the OA can complex with Mn³⁺ to form [Mn(C₂O₄²–)]⁺ and prevent the Mn³⁺ from being reduced to Mn²⁺, leading to the strong oxidizing capacity of the reaction system maintained for a longer time. Atomic force microscopy analysis showed that rod-like CNCs were obtained with an average size of 10–22 nm in diameter and 150–300 nm in length. The crystal structure of as-prepared CNCs-COOH was nearly unchanged, and the crystallinity was 89.2% based on WAXD analysis. Of particular interest, CNCs-COOH suspension with high concentration (>6 wt %) also exhibited the same intriguing chiral nematic liquid crystalline self-assembly behaviors as sulfate CNCs prepared by traditional H₂SO₄ hydrolysis method. This study provides an efficient and cost-effective way to fabricate CNCs-COOH, leading to great potential applications in constructing advanced functional material.