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 (KMnO 4 ) and oxalic acid (OA, H 2 C 2 O 4 ) 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 Mn 3+ to form [Mn(C 2 O 4 2− )] + and prevent the Mn 3+ from being reduced to Mn 2+ , 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 H 2 SO 4 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.

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